pslc.ws · macromolecular syntheses, volume 13 1.procedure for well-defined...

Synthesis of Chain-End-Functionalized Polystyrenes witha Definite Number of Benzyl Bromide Moieties by a Novel

Iterative Divergent Approach and Their SyntheticApplication to Well-Defined Star-Branched Polymers

Akira Hirao, Mayumi Hayashi, Naoki Haraguchi, Akira Matsuo, and TomoyaHigashihara1

Macromolecular Syntheses, Volume 13

1.Procedure for well-defined chain-end-functionalizedpolystyrenes with two, four, eight, sixteen, and thirty-two benzylbromide moieties

All polymerizations and reactions, except for the transformation reaction, were carriedout under high vacuum conditions (10-6 torr) in sealed glass reactors equipped withbreakseals. Experimental details on reagent purification and operations using highvacuum line technique have been well reviewed by Hadjichristidis and his coworkers.2

Large scale experiments can be carried out under an atmosphere of argon.

We have recently developed a novel iterative divergent methodology for the synthesisof well-defined chain-end-functionalized polystyrenes with dendritic benzyl bromidemoieties.3,4 In this methodology, only two sets of the reactions are needed for theentire iterative synthetic sequence: a coupling reaction of the terminal benzyl bromidemoieties with the functionalized 1,1-diphenylalkyl anion prepared from 1,1-bis(3-tert-butyldimethylsilyloxymethylphenyl)ethylene (1)5 and sec-BuLi, and a transformationreaction of the introduced tert-butyldimethylsilyloxymethylphenyl groups into benzylbromide moieties by treatment with LiBr-(CH3)3SiCl. By repeating the two reactions inthe iterative reaction sequence five times, a series of five chain-end-functionalizedpolystyrenes with a definite number of benzyl bromide moieties of two, four, eight,sixteen, and thirty-two in number could successively be synthesized. They areabbreviated as G-1 to G-5.

The first iteration starts with chain-end-functionalized polystyrene with one benzylbromide moiety (G-0), synthesized by the coupling reaction of polystyryllithium (PSLi)with 1-(4-bromobutyl)-4-(tert-butyldimethylsilyloxymethyl)benzene, followed bytransformation with a 1:1 mixed reagent of (CH3)3SiCl and LiBr.5 The terminal benzylbromide moiety of G-0 was coupled with the functionalized 1,1-diphenylalkyl anion tosubstitute two tert-butyldimethylsilyloxymethylphenyl groups. The transformationreaction of the two introduced tert-butyldimethylsilyloxymethylphenyl groups intobenzyl bromide moieties was followed by treatment with LiBr-(CH3)3SiCl in a mixedsolvent of acetonitrile and chloroform. Both reactions proceeded cleanly andquantitatively, thus forming chain-end-functionalized polystyrene with two benzylbromide moieties (G-1). Since G-1 had the same end groups as the starting polymer,G-0, the same two reactions could be repeated in the second iteration to afford chain-end-functionalized polystyrene with four benzyl bromide moieties, G-2. Similarly, thethird, fourth, and fifth iterations were performed successively. The resulting polymerobtained at each stage in the iteration was used as a starting material in the nextiteration. A series of five benzyl bromide-functionalized polystyrenes at the chain-ends, G1 to G5, were thus synthesized. Yields of polymers were virtually quantitativein all cases. At each stage in the iteration, the number of benzyl bromide moietydoubles. The benzyl bromide moieties thus introduced were dendritically distributed atthe chain ends.

Synthesis of Chain-End-Functionalized Polystyrenes . . .

Synthetic procedures are as follows: To a THF (47 mL) solution containing chain-end-functionalized polystyrene with one benzyl bromide moiety, G-0, (4.76 g, 1.07mmol), freeze-dried from its absolute benzene solution for 24 h, was added the 1,1-diphenylalkyllithium derivative prepared from sec-BuLi (1.29 mmol) in heptane (4.30mL) and 1 (1.42 mmol) in THF (14.2 mL) at –78°C for 1 h. The reaction mixture wasallowed to stand in THF at –78°C for an additional 1 h. After terminating the reactionwith a few drops of degassed methanol, the reaction mixture was poured into a largeamount of methanol (300 mL) to precipitate the polymer. The resulting polymer, P-1,(5.04 g, 98%) was purified by repeated reprecipitation from THF into methanol twiceand freeze-drying from its absolute benzene solution for at least 24 h for the nextreaction. The transformation reaction was carried out under a nitrogen atmosphere. A solutionof P-1 (4.89 g, 2.00 mmol for the terminal functional groups) dissolved in drychloroform (30 mL) was added dropwise to a mixture of LiBr (8.68 g, 100 mmol) and(CH3)3SiCl (10.9 g, 100 mmol) in a mixed solvent of dry acetonitrile (30 mL) and drychloroform (90 mL) at 25°C for 0.5 h. The reaction mixture was then allowed to standat 40°C for an additional 5 h, then poured into water and extracted with chloroform (30mL) four times. The combined organic layers were dried over MgSO4. Solvent wasremoved under reduced pressure. The residual polymer (ca. 5 g) was dissolved inTHF (5 mL) and precipitated into a large amount of methanol (ca. 300 mL). Theresulting polymer was purified by peated reprecipitation twice and freeze-dried from itsabsolute benzene solution to afford the expected polymer, G-1 (4.75 g, 96%).Similarly, chain-end functionalized polystyrenes with four (G-2), eight (G-3), sixteen(G-4), and thirty-two (G-5) benzyl bromide moieties were synthesized. A 1.2-foldexcess of the functionalized 1,1-diphenylalkyl anion to each benzyl bromide moietywas always used in the coupling reaction. In the transformation reaction, a 50-foldexcess of LiBr and (CH3)3SiCl to tert-butyldimethylsilyloxymethylphenyl group wasemployed.

1-2. Characterization

Both 1H and 13C NMR spectra were recorded on a Bruker DPX (300 MHz for 1H and 75MHz for 13C) in CDCl3. Size exclusion chromatography (SEC) was obtained at 40°Cusing THF as a carrier solvent with a Tosoh HLC 8020 instrument with UV (254 nm) orrefractive index detection. Fractionation by SEC in THF was performed at 40°C usingthis fully automatic instrument equipped with a TSK-G4000HHR column (300 mm inlength and 21.5 mm in diameter). Vapor pressure osmometry (VPO) measurementsfor determining absolute Mn value were made in benzene solution with a sensitivethermoelectric couple and endosure of very exact temperature control. Static lightscattering (SLS) with a He-Ne laser (λ=632.8 nm) was performed with an OtsukaElectronics SLS-600R instrument using THF or benzene solvent. FT-IR spectra wererecorded on a JEOL JIR-AQS20M FT-IR spectrophotometer. Intrinsic viscosities ofstar-branched polymers were measured with a Ubbelhobe viscometer in toluene at35°C.


G-1: Mn(calcd) = 4.79 kg/mol, Mn(SEC) = 4.23 kg/mol, Mn(VPO) = 4.80 kg/mol, Mn(H NMR) = 4.75

kg/mol, Mw/Mn = 1.04. The degree of end-functionalization observed by 1H NMR was2.0 (calculated = 2). 1H NMR (CDCl3) δ 7.2-6.2 (m, 216H, aromatic), 4.39-4.34 (m, 4H,-CH2Br), 3.4-3.2 (m, 2H, -(Ph)2C-CH2-Ph-), 2.5-1.2 (m, 130H, CH2-CH-), 0.8-0.5 (m,12H, -CH(CH3)CH2CH3). Elemental analysis: Found: C, 88.50; H, 7.76; Br, 3.57%;Calculated for C356H360Br2: C, 89.10; H, 7.56; Br, 3.33%. FT-IR (KBr, cm-1): 1208 (-CH2Br).


kg/mol, Mw/Mn = 1.04. The degree of end-functionalization observed by 1H NMR was3.9 (calcd = 4). 1H NMR (CDCl3) δ 7.2-5.9 (m, aromatic), 4.40-4.34 (m, 8H, -CH2Br),3.4-3.0 (m, 6H, -(Ph)2C-CH2-Ph-), 2.5-1.2 (m, CH2-CH-), 0.8-0.4 (m, 24H,-CH(CH3)CH2CH3). Elemental analysis: Found; C, 86.32; H, 7.62; Br, 5.96%;Calculated for C400H410Br4: C, 86.71; H, 7.46; Br, 5.83%. FT-IR (KBr, cm-1): 1208 (-CH2Br).


kg/mol, Mw/Mn = 1.03. The degree of end-functionalization observed by 1H NMR was8.0 (calcd = 8). 1H NMR (CDCl3) δ 7.2-5.8 (m, aromatic), 4.36-4.32 (m, 16H, -CH2Br),3.5-2.7 (m, 8H, -(Ph)2C-CH2-Ph-), 2.5-1.2 (m, CH2-CH-), 0.8-0.4 (m, 48H,-CH(CH3)CH2CH3). Elemental analysis: Found: C, 83.11; H, 7.55; Br, 9.72%;Calculated for C476H498Br8: C, 83.35; H, 7.32; Br, 9.33%. FT-IR (KBr, cm-1): 1208 (-CH2Br).


kg/mol, Mw/Mn = 1.04. The degree of end-functionalization observed by 1H NMR was15.9 (calcd = 16). 1H NMR (CDCl3) δ 7.2-5.7 (m, aromatic), 4.35 (s, 32H, -CH2Br), 3.5-2.6 (m, 30H, -(Ph)2C-CH2-Ph-), 2.4-1.2 (m, CH2-CH-), 0.8-0.2 (m, 96H,-CH(CH3)CH2CH3). Elemental analysis: Found: C, 79.39; H, 7.76; Br, 13.13%;Calculated for C636H682Br16: C, 79.52; H, 7.16; Br, 13.32%. FT-IR (KBr, cm-1): 1208 (-CH2Br).


kg/mol, Mw/Mn = 1.03. The degree of end-functionalization observed by 1H NMR was32.0 (calcd = 32). 1H NMR (CDCl3) δ 7.2-5.5 (m, aromatic), 4.33 (s, 64H, -CH2Br), 3.5-2.6 (m, 62H, -(Ph)2C-CH2-Ph-), 2.4-1.2 (m, CH2-CH-), 0.8-0.3 (m, 192H,-CH(CH3)CH2CH3). Elemental analysis: Found: C, 75.50; H, 7.46; Br, 17.00%;Calculated for C956H1049Br32: C, 76.05; H, 7.00; Br, 16.95%. IR (KBr, cm-1): 1208 (-CH2Br).


Figure 1. SEC profiles of chain-end-fucntionalizedpolystyrenes with 2 (G-1), 4 (G-2) , 8 (G-3), 16 (G-4),

and 32 (G-5) benzyl bromide moieties.

Figure 2. 1H NMR spectrum of chain-end-functionalized polystyrene with 16 benzyl bromidemoieties (G-4)

34 36 38 40 42 44 46 48

Elution Count

G-1G-2G-3G-4

G-5

0. 02. 04. 06. 08. 0ppm

CH2 Br


A3

A5

A9

AB8

A17

A33


2-1. Synthesis of regular 3-, 5-, 9-, 17-, and 33-arm star-branchedpolystyrenes and AB8 asymmetric star-branched polymers.

Regular type 3-, 5-, 9-, 17-, and 33-arm star-branched polystyrenes were synthesizedby coupling G-1 ~ G-5 with 1,1-diphenylethylene (DPE)-end-capped polystyryllithiumsin THF at –40°C for 1 h. After quenching the reactions with degassed methanol, thereaction mixtures were poured into methanol to precipitate the polymers. Yields of thestar-branched polymers were virtually quantitative. The objective star-branchedpolystyrenes were then isolated in more than 90% yield by fractionational precipitationusing cyclohexane and hexanes mixed solvents (4/1 ~ 1/1, v/v) at 5°C. They werereprecipitated from THF in to methanol twice and freeze-dried from their benzenesolutions. Since the polystyrenes used as arms were present in solution, they wererecovered by precipitating into methanol. These poloystyrenes were also purified byfractional precipitation to remove small amounts of stars. The resulting star and armpolymers were characterized by 1H NMR, SEC, SLS, and viscosity measurements. A representative procedure of the 33-arm star-branched polystyrene is as follows:Styrene (1.40 g, 13.4 mmol) in THF (14.0 mL) was added with vigorous stirring to sec-BuLi (0.270 mmol) in heptane (5.56 mL) at –78°C and the reaction mixture wasallowed to stir for an additional 20 min, followed by treatment with DPE (0.405 mmol)in THF (6.35 mL) at –78°C for 15 min for end-capping. Then, chain-end-functionalizedpolystyrene with thirty-two benzyl bromide moieties, G-5, (0.0848 g, 0.00563 × 32 =0.180 mmol for benzyl bromide moiety) dissolved in THF (2.54 mL) was added to theDPE-end-capped polystyryllithium at –78°C. The reaction mixture was allowed tostand at –40°C for an additional 1 h. After terminating the reaction with degassedmethanol (5 mL), the reaction mixture was poured into a large amount of methanol(300 mL) to precipitate the polymer. The star-branched polystyrene was isolatednearly quantitatively by fractionational precipitation as follows. The precipitatedpolymer (1.40 g) dissolved in cylcohexane (400 mL) was cooled to 5°C. Then, hexane(300 mL) was added slowly to the polymer solution overr 2 h and the precipitatedpolymer was collected by filtration. The polymer collected (0.993 g, 95%) wasreprecipitated twice from THF into methanol and freeze-dried from its absolutebenzene solution (0.980 g, 94%). Similarly, 3-, 5-, 9-, and 17-arm star-branchedpolystyrenes were synthesized. A 1.5-fold excess of polystyryllithium end-capped withDPE was usually used toward each benzyl bromide moiety. A series of chain-end-functionalized polystyrenes with a definite number of benzylbromide moieties are also useful precursory polymers for the synthesis of asymmetricstar-branched polymers whose arms differ in molecular weight and composition.6,7

Various AA’n and ABn asymmetric stars may be synthesized by coupling G seriespolymers with other living anionic polymers. In practice, novel asymmetric AB8 star-branched polymers could be readily and quantitatively synthesized by the couplingreaction of the same G-3 (Mn = 6.85 kg/mol, Mn of polystyrene segment = 4.56 kg/mol)with living anionic polymers of isoprene, 2-vinylpyridine, and tert-butyl methacrylatesimilar to the synthesis of regular star-branched polystyrenes. Representative


experimental details are as follows: Isoprene (21.6 mmol) in heptane (8.50 mL) waspolymerized with sec-BuLi (0.361 mmol) in heptane (7.00 mL) at 40°C for 2 h and thepolymerization mixture was cooled to -78°C. THF (11.9 mL) was added to the mixtureand subsequently DPE (0.484 mmol) in THF (4.22 mL) was added to end-cap thepropagating chain-end anion at -78°C for 10 h. Then, G-3 (0.202 g, 0.236 mmol forbenzyl bromide moiety) in THF (5.40 mL) was added. 2-Vinylpyridine (18.4 mmol) inTHF (21.2 mL) was polymerized with 1,1-diphenyl-3-methylpentyllithium preparedfrom DPE (0.462 mmol) in THF (4.50 mL) and sec-BuLi (0.355 mmol) in heptane (6.98mL) at -78°C for 4 h and then G-3 (0.201 g, 0.235 mmol for benzyl bromide moiety) inTHF (5.38 mL) was added. Tert-butyl methacrylate (11.9 mmol) in THF (12.0 mL) waspolymerized with diphenylmethylpotassium (0.356 mmol) in THF (8.62 mL) at -78°Cfor 2 h and then G-3 (0.201 g, 0.235 mmol for benzyl bromide moiety) in THF (5.38mL) was added. The coupling reactions were carried out in THF at –40°C for 24 h andquenched with degassed methanol. The resulting AB8 star-branched polymers, aswell as arm polymers, were isolated by fractionation with SEC. They were purified byreprecipitation twice from THF into methanol, heptane, or water and freeze-dryed fromtheir benzene solutions. They were characterized by 1H NMR, SEC, and SLS.

2-2. Characterization of regular and asymmetric star-branchedpolystyrenes Well-defined chain structures and branched architectures of the resulting star-branched polymers synthesized here were confirmed by 1H NMR, SEC and SLS. Theexpected arm numbers of the regular 3-, 5-, 9-. 17-, and 33-arm star branchedpolystyrenes were demonstrated by agreement between their g’ values determinedexperimentally and those calculated from equations based on a theoretical model orobserved in previous experimental results.8

The 1H NMR spectra of star-branched polystyrenes are as follows: 1H NMR δ 7.2-5.7(m, aromatic), 3.5-2.7 (m, -(Ph)2C-CH2-Ph-), 2.5-0.8 (m, CH2-CH-), 0.7-0.5 (m,-CH(CH3)CH2CH3).

3-Arm star-branched polymer: Mn(calcd) = 17.4 kg/mol, Mn(SEC) = 14.5 kg/mol, Mw (calcd) =17.8 kg/mol, Mw(SLS) = 17.8 kg/mol (dn/dc = 0.189 in THF at 25°C), Mw/Mn (SEC)= 1.03.

5-Arm star-branched polymer: Mn(calcd) = 25.8 kg/mol, Mn(SEC) = 18.7 kg/mol, Mw(calcd) =26.8 kg/mol, Mw(SLS) = 26.6 kg/mol (dn/dc = 0.187 in THF at 25°C), Mw/Mn (SEC)= 1.04.

9-Arm star-branched polymer: Mn(calcd) = 42.8 kg/mol, Mn(SEC) = 23.8 kg/mol, Mw(calcd) =44.0 kg/mol, Mw(SLS) = 44.7 kg/mol (dn/dc = 0.187 in THF at 25°C), Mw/Mn (SEC)= 1.03.

17-Arm star-branched polymer: Mn(calcd) = 84.2 kg/mol, Mn(SEC) = 34.9 kg/mol, Mwcalcd) =88.1 kg/mol, Mw(SLS) = 87.6 kg/mol (dn/dc = 0.189 in THF at 25°C) and Mw(SLS) = 88.0kg/mol (dn/dc = 0.101 in benzene at 25°C) Mw/Mn (SEC)= 1.05.


33-Arm star-branched polymer: Mn(calcd) = 186 kg/mol, Mn(SEC) = 70.6 kg/mol, Mw(calcd) =190 kg/mol, Mw(SLS) = 196 kg/mol (dn/dc = 0.185 in THF at 25 C) and Mw(SLS) = 191kg/mol (dn/dc = 0.100 in benzene at 25°C), Mw/Mn (SEC)= 1.02.

Since Mn values of all polystyryllithiums used as arm segments are ca. 5 kg/mol(similar to those of polystyrene parts of G series polymers), the resulting polymers canbe regarded as regular-type star-branched polystyrenes. One of the best solutions toascertain branched architecture of a regular star-branched polymer is to determine g’values defined as [η]star / [η]linear where [η]star and [η]linear are intrinsic viscosities of thestar-branched polymer and linear polymer with the same molecular weight measuredunder the same conditions. The intrinsic viscosities of the star-branched polystyrenessynthesized in this study were measured in toluene at 35°C. The values of [η]linear

were calculated from the established equation, [η] = 1.29 × 10-4Mw0.71.9 Since the good

correlation between g’ value and arm number has been established based on thetheoretical models and experimental results, g’ values were also calculated by thefollowing equation (1) proposed by Douglas, Roovers, and Freed.10

g’ = {[(3f-2)/f2]0.58[0.724 – 0.015(f-1)]}/0.724 (1) These results are summarized in the Table. As expected, viscosity values of the star-branched polystyrenes were always smaller than those of linear counterparts. Thereis a fairly good consistency between the g’ values experimentally determined andthose calculated from the equation except for the case of the 33-arm star-branchedpolystyrene. The expected branched architectures of the 3-, 5-, 9-, and 17-arm star-branched polystyrenes are thus supported.

In contrast, the experimental g’ value (0.13) of the 33-arm star-branched polystyrenewas definitely higher than the calculated value of 0.08. Similar trends have beenreported in the cases of star-branched polymers having many arms; ie., 32, 64, and128 arms.11,12 We therefore calculated the g’ value of our 33-arm star-branchedpolystyrene by using the following equation (2) based on the experimental resultsproposed by Roovers.13

log g’ = 0.36 – 0.80 log f (f = arm number, f > 6) (2)

The g’ value thus calculated was 0.14, close to the experimental value of 0.13. Thus,the expected branched architecture of the 33-arm star-branched polystyrene is alsosupported.


arm number Mw (kg/mol) [η] dL/g g’ value

star linear exptl eq (1) eq (2)

3

5

9

17

33

17.8

26.6

44.7

87.6

196

0.111 0.134

0.114 0.179

0.119 0.212

0.109 0.417

0.0937 0.738

0.83 0.83

0.64 0.63

0.46 0.42 0.40

0.26 0.24 0.24

0.13 0.082 0.14

Table. Intrinsic viscosity and g' values for 3-, 5-, 9-, 17-, and 33-arm star-branched polymers.

AB8 asymmetric star-branched polymer: A segment (polystyrene, Mn(SEC) = 4.63kg/mol), B segment (polyisoprene, Mn(SEC) = 4.19 kg/mol). Mn(calcd) = 39.7 kg/mol, Mn(SEC)

= 32.5 kg/mol, Mn(NMR) = 40.5 kg/mol, Mw(calcd) = 40.5 kg/mol, Mw(SLS) = 41.2 kg/mol (dn/dc= 0.119 in THF at 25°C). Mw/Mn (SEC)= 1.02. Composition: [styrene]/[isoprene] =42/476 (mol/mol determined by 1H NMR), 42/464 (mol/mol, calculated).

AB8 asymmetric star-branched polymer: A segment (polystyrene, Mn(SEC) = 4.56kg/mol), B segment (poly(2-vinylpyridine), Mn(SEC) = 5.36 kg/mol). Mn(calcd) = 48.4 kg/mol,Mn(SEC) = 24.7 kg/mol, Mn(NMR) = 49.0 kg/mol, Mw(calcd) = 49.6 kg/mol, Mw(SLS) = 49.9 kg/mol(dn/dc = 0.179 in THF at 25°C). Mw/Mn (SEC)= 1.03. Composition: [styrene]/[isoprene] =41/396 (mol/mol determined by 1H NMR), 41/390 (mol/mol, calculated).

AB8 asymmetric star-branched polymer: A segment (polystyrene, Mn(SEC) = 4.56kg/mol), B segment (poly(tert-butyl methacrylate), Mn(SEC) = 4.87 kg/mol). Mn(calcd) = 44.4kg/mol, Mn(SEC) = 26.2 kg/mol, Mn(NMR) = 45.9 kg/mol, Mw(calcd) = 45.8 kg/mol, Mw(SLS) = 46.4kg/mol (dn/dc = 0.0968 in THF at 25°C). Mw/Mn (SEC)= 1.03. Composition:[styrene]/[isoprene] = 41/275 (mol/mol determined by 1H NMR), 41/265 (mol/mol,calculated).


3.References

1. Polymeric and Organic Materials Department, Graduate School of Science andTechnology, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku,Tokyo 152-8552, JAPAN.

2. Hadjichristidis, N.; Iatrou, H.; Pispas, S.; Pitsikalis, M. J. Polym. Sci., Polym.Chem. 2000, 32, 3211.

3. Hirao, A.; Hayashi, M.; Haraguchi, N. Macromol. Symp. 2002, 183, 11. 4. Hirao, A.; Haraguchi, N. Macromolecules 2002, 35, 7224.5. Hirao, A.; Hayashi, M. Macromolecules 1999, 32, 6450.6. Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Chem. Rev. 2001, 101,

3747.7. Hirao, A.; Hayashi, M.; Tokuda, Y.; Haraguchi, N. Higashihara, T.; Ryu, S-W.

Polym J. 2002, 34, 633.8. Bauer, B.; Fetters, L. J. Rubber Chem. Tech. 1978, 51, 406.9. Corbin, N.; Prud’homme, J. J. Polym. Sci., Polym. Phys. 1977, 15, 1937.10.Douglas, J. F.; Roovers, J.; Freed, K. F. Macromolecules 1985, 18, 201.

Figure 3. SEC profiles of crude reaction mixture (A) and33-arm star-branched polystyrene isolated by fractional

precipitation (B).

40 45 50 55 60 65Elution Count

(A)

(B)


11.Zhou, L. L.; Hadjichristidis, N.; Toporowski, P. M.; Roovers, J. Rubber Chem.Tech. 1992, 65, 303.

12.Roovers, J.; Zhou, L. L.; Toporowski, P. M.; Zwan, M. V.; Iatrou, H.;Hadjichristidis, N. Macromolecules 1993, 26, 4324.

13.Roovers, J. in Star and Hyperbranched Polymers 1999, Marcel Dekker: NewYork,; pp 285-341.

A One Step Synthesis of Ligands for Transition MetalMediated Living Radical Polymerization of Methacrylates

David M Haddleton,1 Simon Harrisson,1 Alexander M. Heming2

1a (R = n-C3H7) 1b (R = n-C5H11)

1.Procedure, N-propyl 2-pyridylmethanimine (1a)

2-Pyridine carboxaldehyde (20 mL, 0.21 mol) and diethyl ether (20 mL) were added toa flask containing dried magnesium sulphate (BDH) (5 g). The flask was cooled to 0oCand n-propylamine (19 mL, 0.25 moles) was added slowly. The mixture was removedfrom the ice bath and stirred for two hours at 25oC prior to filtration. Diethyl ether wasremoved by rotary evaporation and the resulting yellow oil was purified by vacuumdistillation.

The product was obtained as a straw-colored oil (bp. 43oC at 7 × 10-2 mbar). Yield =98%

2.Characterization, N-propyl 2-pyridylmethanimine (1a)

CHN analysis returned 73.1 % C, 8.2 % H, 18.7 % N, compared to theoretical 72.9 %C, 8.2 % H, 18.9% N.

The 300 MHz 1H NMR spectrum (Note 1) in CDCl3 at ambient temperature showsaromatic absorptions from the pyridyl ring at 8.63 (d, 1H), 8.00 (d, 1H), 7.69 (t, 1H)and 7.27 (t, 1H) ppm from TMS. The proton α to the pyridyl ring returns a singlet at


8.39 ppm, while the protons of the propyl group are found at 3.64 (t, 2H α to N, J = 4.4Hz), 1.76 (sx, 2H β to N, J = 4.4 Hz), and 0.70 (t, 3H, J = 4.4 Hz) ppm.

The 75 MHz 13C NMR spectrum in CDCl3 at ambient temperature shows a C=N peakat 161.0 ppm, aromatic peaks at 154.1. 148.7, 135.8, 123.9 and 120.5 ppm, andpeaks corresponding to the propyl group at 62.6, 22.3 and 11.3 ppm.

The IR spectrum (Note 2) shows C-H stretches at 3054, 3009 and 2961-2834 cm-1, aC=N stretch at 1651 cm-1 and aromatic ring stretches at 1587, 1567, 1467 and 1436cm-1.

The chemical ionization mass spectrum returned a major peak at m/z = 149 (M + H).

3.Procedure, N-pentyl 2-pyridylmethanimine (1b)

2-Pyridine carboxaldehyde (20 mL, 0.21 mol) and diethyl ether (20 mL) were added toa flask containing dried magnesium sulphate (BDH) (5 g). The flask was cooled to 0oCand n-pentylamine (29.0 mL, 0.25 moles) was added slowly. The mixture was stirredfor two hours at 25oC prior to filtration. Diethyl ether was removed by rotaryevaporation and the resulting yellow oil was purified by vacuum distillation.

The product was obtained as a yellow oil (bp. 60oC at 5 × 10-2 mbar). Yield = 96.7 %

4.Characterization, N-pentyl 2-pyridylmethanimine

CHN analysis returned 74.4 % C, 9.1% H, 15.9% N, compared to theoretical 74.9 %C,9.2 %H, 12.83 %N.

The 300 MHz 1H NMR spectrum in CDCl3 at room temperature shows aromaticabsorptions from the pyridyl ring at 8.62 (d, 1H), 7.98 (d, 1H), 7.72 (t, 1H) and 7.30 (t,1H) ppm from TMS. The proton α to the pyridyl ring returns a singlet at 8.36 ppm,while the protons of the pentyl group are found at 3.66 (t, 2H α to N), 1.58 (quintet, 2Hβ to N, J = 7.35 Hz), 1.33 (m, 4H) and 0.89 (t, 3H) ppm.

The 75 MHz 13C NMR spectrum in CDCl3 at room temperature shows a C=N peak at161.3 ppm, aromatic peaks at 154.4. 149.7, 136.1, 124.2 and 120.8 ppm, and peakscorresponding to the pentyl group at 61.2, 30.1, 29.2, 22.2, and 13.7 ppm.

The IR spectrum shows C-H stretches at 3010, 2923 and 2853 cm-1, a C=N stretch at1650 cm-1, aromatic ring stretches at 1587, 1567, 1467 and 1435 cm-1, and othermajor absorbances at 1366, 1331, 1291, 1144 and 1043 cm-1.The chemical ionization mass spectrum returned two major peaks at m/z = 219 (M +H) and 203 (M - CH3).

A One Step Synthesis of Ligands

5.Procedure, Copper(I) mediated polymerization of MMA with N-propyl-2-pyridylmethanimine

Cu(I)Br (0.134 g, 9.32 × 10-4 moles) and a dry magnetic follower were charged to a drySchlenk tube. The tube was sealed with a rubber septum prior to three vacuum / N2

cycles. Toluene (10 mL), MMA (10 mL, 9.36 × 10-2 moles) and N-propyl-2-pyridylmethanimine (0.279 g, 1.87 × 10-3 moles) were added under N2. The Schlenktube was subjected to three freeze pump thaw cycles and subsequently heated to90oC with constant stirring. Once the reaction temperature had been reached, ethyl-2-bromoisobutyrate (0.136 mL, 9.36 × 10-4 moles) was added under N2 (t = 0). Sampleswere removed at 30-60 minute intervals using a degassed syringe for molecularweight and conversion analysis. The reaction was stopped after 300 minutes, with afinal conversion of 89.3 %. Mn = 8760 g mol-1(Theoretical Mn = 8930), PDi = 1.20.

6.Characterization, Copper(I) mediated polymerization of MMA([M]:[I]:[Cu]:[L] = 100:1:1:2) with N-propyl-2-pyridylmethanimine

Molecular weight was measured by size exclusion chromatography on a PolymerLaboratories System using THF as the eluent at 1.0 ml min-1 and equipped with a PLautoinjector, a PL-gel 5 µm (50 × 7.5 mm) guard column, two PL-gel 5 µm (300 × 7.5mm) mixed-C columns and a refractive index detector. The system was calibrated withnarrow poly(methyl methacrylate) standards with peak weights ranging from 200 to1.577 × 106 g mol-1, obtained from Polymer Laboratories, except for MMA dimer, trimerand tetramer, which were prepared by catalytic chain transfer at the University ofWarwick. Samples were prepared by dissolving the reaction mixture in THF to anapproximate polymer concentration of 4 mg mL-1. The resulting solutions were passedthrough a short column of basic alumina to remove copper, then through a 0.2 µmfilter before analysis.

Conversions were measured by gravimetry. A sample was accurately weighed into apre-weighed aluminium pan and then volatile solvents and monomers were removedunder vacuum in an oven at 60°C until constant sample weight was reached.

The conversion and molecular weight results thus obtained are shown in Table 1.


Time (min) Conversion (%) Mn

(g mol-1)

PDi

30 22.1 3980 1.2560 37.3 4820 1.22120 58.2 6580 1.20180 72.8 7930 1.17240 82.7 8330 1.18300 89.3 8760 1.20

Table 1. Conversion and molecular weight data for copper-mediated polymerization of methyl methacrylate withN-propyl 2-pyridyl-methanimine.

7.Procedure, Copper(I) mediated polymerization of styrene with N-pentyl 2-pyridyl methanimine.

Cu(I)Br (0.131 g, 9.1 × 10-4 mol) and a dry magnetic follower were charged to a drySchlenk tube. The tube was sealed with a rubber septum prior to three vacuum / N2

cycles. Xylene (20 mL), styrene (10 mL, 8.73 × 10-2 moles) and ethyl-2-bromoisobutyrate (0.13 ml, 9.1 × 10-4 mol) were added under N2. The Schlenk tubewas subjected to three freeze pump thaw cycles and subsequently heated to 110oCwith constant stirring. Once the reaction temperature had been reached, N-pentyl-2-pyridylmethanimine (0.28 mL, 1.8 × 10-3 mol) was added under N2 (t = 0). Sampleswere periodically removed using a degassed syringe for molecular weight andconversion analysis. The reaction was stopped after 360 minutes, with a finalconversion of 77.9 %. Mn = 5270 (Theoretical Mn = 7900 g mol-1), PDi = 1.29. 8.Characterization, Copper(I) mediated polymerization of styrene

with N-pentyl-2-pyridylmethanimine

Molecular weight was measured by size exclusion chromatography on a PolymerLaboratories System using THF as the eluent at 1.0 ml/min and equipped with a PLautoinjector, a PL-gel 5 µm (50 × 7.5 mm) guard column, two PL-gel 5 µm (300 × 7.5mm) mixed-C columns and a refractive index detector. The system was calibrated withnarrow polystyrene standards with peak weights ranging from 580 to 3.15 × 106 gmol-1, obtained from Polymer Laboratories. Samples were prepared by dissolving thereaction mixture in THF to an approximate polymer concentration of 4 mg/mL. Theresulting solutions were passed through a short column of basic alumina to removecopper, then through a 0.2 µm filter before analysis.

A One Step Synthesis of Ligands

Conversions were measured by gravimetry. A sample was accurately weighed into apre-weighed aluminium pan. Volatile solvents and monomers were then removedunder vacuum at 60°C until constant sample weight was reached.

The conversion and molecular weight results thus obtained are shown in Table 2.

Time (min) Conversion (%) Mn

(g mol-1)

PDi

50 0 0 —210 9.33 950 1.19330 18.6 1480 1.17975 63.9 4250 1.231110 71.3 4820 1.261265 77.9 5270 1.29

Table 2. Conversion and molecular weight data for copper-mediated polymerization of styrene with N-pentyl 2-pyridylmethanimine.

9. Methods of preparation.

N-n-alkyl pyridyl methanimines are useful ligands for the copper-mediated livingpolymerization of many monomers, including many functionalized methacrylates3,4 andstyrene5. A wide range of alkyl substituents may be used,6 allowing adjustment of thesolubility of the resulting copper complexes. Appropriate ligand selection allowshomogeneous polymerizations to be carried out across a wide range of temperatures.7

10.Notes

1. A Bruker 300MHz NMR spectrometer is used.2. A Bruker Vector 22 FTIR spectrometer equipped with a Golden Gate diamond

attenuated total reflection (ATR) sample platform is used.

11.References

1. Department of Chemistry, University of Warwick, CV4 7AL, UK. 2. Current address: Bioperformance Research Section, Syngenta, Jealotts Hill

Research Station, Bracknell, RG42 6EY, UK. 3. A. Marsh, A. Khan, D. M. Haddleton, and M. J. Hannon, Macromolecules; 32,

8725 (1999). 4. S Perrier, S P Armes , X. S. Wang, F. Malet and D M. Haddleton, J Pol Sci,

Polym. Chem. 39, 1696, (2001).


5. S. Perrier, D. Berthier, I. Willoughby, D. Batt-Coutrot, and D. M. Haddleton,Macromolecules, 35, 2941 (2002).

6. D. M. Haddleton, M. C. Crossman, B. H. Dana, D. J. Duncalf, A. M. Heming, D.Kukulj, and A. J. Shooter, Macromolecules 32, 2110 (1999).

7. D. M. Haddleton, D. J. Duncalf, A. M. Heming, D. Kukulj, and A. J. ShooterMacromolecules 31, 2016, (1998).

Synthesis of AB Diblock Polyampholytes via GTPAndrew B. Lowe1

1.Procedure

Materials:

Unless stated otherwise, all chemicals were purchased from Aldrich. 2-(Dimethylamino)-ethyl methacrylate (DMAEMA) was purified by passing through acolumn of basic alumina to remove the inhibitor, stored over CaH2 below 0°C, anddistilled immediately prior to use. The initiator, 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene (MTS) was distilled under high vacuum and stored in a graduated Schlenkflask under a nitrogen atmosphere at below 0°C. The catalyst, tetra-n-butylammoniumbibenzoate (TBABB), was prepared in-house according to the method of Dicker et al.2,and was stored as a solid under vacuum. The polymerization solvent, THF, was driedover sodium wire prior to reflux over potassium metal for three days. This THF was


collected under a dry nitrogen purge and stored over 4 Å molecular sieves under anitrogen atmosphere.

a. Synthesis of 2-tetrahydropyranyl methacrylate (THPMA)

THPMA was prepared by the acid-catalyzed esterification of methacrylic acid (MAA)with 3,4-dihydro-2H-pyran using a modification of the method of Hertler.3 To a 1 L,three-necked, round-bottomed flask equipped with a magnetic stir-bar, refluxcondenser, inert gas inlet, and addition funnel was added 3,4-dihydro-2H-pyran (125mL, 1.37 mol) and 10 drops of 50% sulfuric acid. This mixture was stirred at roomtemperature for approximately 20 min. A mixture of MAA (116 mL, 1.49 mol), 3,4-dihydro-2H-pyran (125 mL, 1.37 mol), and phenothiazine (1.0 g, 5.0 mmol) was addedvia the addition funnel. The reaction mixture was then heated at 54°C for 25 h. Aftercooling to room temperature, solid sodium hydrogen carbonate (10.0 g, 0.119 mol)and anhydrous sodium sulfate (40.0 g, 0.282 mol) were added and the reactionmixture was left stirring overnight. The mixture was filtered and treated with CaH2 (1.0g, 23.8 mmol), phenothiazine (1.0 g, 5.0 mmol) and 2,2-diphenyl-1-picrylhydrazyl(DPPH, 0.2 g, 0.51 mmol). The excess 3,4-dihydro-2H-pyran was removed underreduced pressure. The remaining mixture was distilled at 70°C under reducedpressure, yielding approximately 100 mL of THPMA. THPMA was then further purifiedby passing over a column of basic alumina to remove residual traces of MAA. Twosubsequent vacuum distillations, from CaH2/DPPH, yielded THPMA of sufficient purityfor GTP.

b. GTP synthesis of the DMAEMA-THPMA AB diblock copolymers

All glassware was dried overnight at 150°C and assembled hot under a nitrogen purgeand then flamed out under dynamic vacuum to remove any residual surface moisture.All polymerizations were performed in a 250 mL, three-necked round-bottomed flaskequipped with a magnetic stir-bar and rubber septa for liquid transfers. All liquidtransfers were performed using double-tipped needles. Polymerizations were carriedout at room temperature (~22°C). Polymerization exotherms were monitored using adigital thermometer. A typical polymerization procedure for an AB diblock copolymeris detailed below:

To the polymerization flask was added THF (~100 mL) via a double tipped needle.The catalyst, TBABB (~20.0 mg), was added as a solid through a sidearm of thepolymerization flask. This was added to MTS (typically 0.20 mL, 1.62 mmol), and thereaction mixture was stirred for approximately 30 min. Subsequently, freshly distilledDMAEMA (10.0 mL, 59.3 mmol) was added dropwise to the reaction flask and theexotherm was monitored as stated above. (DMAEAM was polymerized first in allcases). Once the exotherm had abated, a 1 mL sample was extracted via syringe forGPC analysis. Next, freshly distilled THPMA (6 mL for a theoretical molar compositionof 60:40) was added dropwise to the living PDMAEMA solution and the reaction

Synthesis of AB Diblock Polyampholytes via GTP

exotherm monitored. Finally, once the reaction had cooled to room temperature, asmall aliquot of the diblock copolymer was extracted for GPC analysis. The blockcopolymer was isolated by removing the THF under vacuum, followed by drying invacuo overnight at room temperature.

c. Removal of the THP protecting group

The THP protecting group was removed by two different methods. For thermolyses,the solid copolymer was heated in a vacuum oven at 145°C for ~24 h. Alternatively,for acid hydrolyses, the copolymer (~2.0 g) was stirred in 0.1 M HCl until dissolution,giving an optically transparent solution.4,5,6 Where possible, the resulting diblockpolyampholyte was recovered via precipitation at the isoelectric point. This method ofrecovery inevitably led to the copolymers being isolated in their partially ionized form.

d. (Co)polymer characterization

Characterization in Organic Solvents by GPC. Molecular weights andpolydispersities of the precursor PDMAEMA homopolymers and the DMAEMA-block-THPMA copolymers were determined by gel permeation chromatography (GPC) usinga Polymer Labs mixed "D" column, connected to an RI detector, and a Knauer UVdetector. The mobile phase was HPLC-grade THF stabilized with butylatedhydroxytoluene, at a flow rate of 1 mL - min-1. The GPC was calibrated with a seriesof four PMMA standards with molecular weights ranging from 2000 to 29,400.

1H NMR Spectroscopy. 1H NMR spectra were recorded using a Bruker AC-P250Fourier transform NMR spectrometer. Spectra were recorded in either CDCl3 orDMSO-d6 using residual nondeuterated solvent (CHCl3 or DMSO) as an internalreference.

Characterization in Water by Acid Titration. An acid-hydrolyzed, DMAEMA-MAAblock (50 mg) was dispersed or dissolved in 5 g of doubly distilled deionized water.The dispersed copolymer was dissolved by the addition of 5-6 drops of 0.5 M HCl(resulting copolymer solution pH ~2). The copolymer solution was titrated with stirringusing 0.5 M KOH solution (Aldrich); the solution pH was recorded using a HANNAInstruments 8521 pH meter calibrated with buffer solutions at pH 4 and pH 7.

Aqueous GPC. The molecular weights and molecular weight distributions of thepolyampholytes were determined via aqueous gel permeation chromatography (GPC).The aqueous GPC system comprised a Pharmacia Biotech "Superdex" 200 HR 10/30column connected to a ERC-7517A RI detector and a Polymer Labs LC 1200 UV/visdetector. The mobile phase consisted of a buffered solution oftris(hydroxymethyl)aminomethane (TRIZMA). TRIZMA·HCl, 2.21 g, and TRIZMA base,4.36 g, were dissolved in 1 dm3 of 1.0 M NaCl solution to give a 0.05 M solution ofTRIZMA, at pH 8.5. The TRIZMA solution was vacuum-filtered and then sonicatedand degassed for 30 min. This mobile phase was used at a flow rate of 1.50 mL-min-1.


The column temperature was maintained at 30°C. A series of poly(ethylene oxide)standards were used as calibrants.

2.Results

sample ID theor MnobsdMn

atheoretical molarcomposition

observed molarcompositionb Mw/Mn

a

AB1 8 000 8 500 80:20 77:23 1.08AB2 24 000 24 700 80:20 82:18 1.16AB3 32 500 35 700 60:40 64:36 1.15AB4 39 200 34 000 50:50 51:49 1.22AB5 49 400 42 400 40:60 43:57 1.19

Table 1. Summary of the Theoretical and Observed Number-Average Molecular Weights (Mn), the Theoreticaland Observed Block Copolymer Compositions, and the Polydispersities of the DMAEAM-block-THPMA

Precursor Copolymersa As determined by GPC. b As determined by 1H NMR spectroscopy.

Figure 1. Typical GPC traces of a DMAEMAhomopolymer and the corresponding

DMAEMA-block-THPMA copolymer in THF.


Figure 2. 1H NMR spectrum of a 64-36 DMAEMA-block-THPMA copolymer recorded in CDCl3

Figure 3. 1H NMR spectrum (DMSO-d6) of the 82-18 DMAEMA-block-MAA copolymer obtained from the acid hydrolysis of a DMAEMA-

block-THPMA precursor copolymer (AB2)


sample ID block copolymer composition DMAEMA:MAA calcd IEP obsd IEPa

AB1-D 77:23 8.52 -AB2-D 82:18 8.65 8.56AB3-D 64:36 7.89 7.40AB4-D 51:49 6.86 6.74AB5-D 43:57 5.83 5.62

Table 1. Summary of the Calculated and Observed Isoelectric Points of the Zwitterionic DMAEAM-block-MAACopolymers

a Taken as the midpoint of the precipitation range.

3.NOTES

1. Since THPMA is prepared using an excess of MAA, it is crucial that theTHPMA be sufficiently pure since any residual MAA will ‘kill’ thepolymerization.

2. While the THP protecting group may be removed by either thermolyses oracid hydrolysis, the hydrolysis route is the preferred method of choice.Thermolysis of PTHPMA homopolymer for an extended period (24 h) didindeed lead to the formation of PMAA, but also to the subsequentdehydration of the PMAA residues to form both inter- and intramolecularanhydride linkages.

3. The resulting DMAEMA-MAA, and precursor DMAEMA-THPMA blockcopolymers, exhibit interesting aqueous solution properties and alsofacilitate the preparation of zwitterionic shell-cross linked micelles.6,7

Figure 4. TGA trace of a THPMA homopolymer, showing theinitial loss of the THP protecting group and the subsequent

dehydration of the PMAA to poly(methacrylic anhydride)


4.References

1. University of Southern Mississippi, Department of Chemistry and Biochemistry,Hattiesburg, MS 39406.

2. Dicker, I. B.; Cohen, G. M.; Farnham, W. B.; Hertler W. R.; Laganis, E. D.; Sogah, D.Y. Macromolecules 1990, 23, 4034-4041.

3. Hertler, W. R. U.S. Patent 5,072,029, 1991. 4. Kearns, J. E.; McLean, C. D.; Soloman, D. H. J. Macromol. Sci., Chem. 1974, A8 (4),

673-685.5. Lowe, A. B.; Billingham, N. C.; Armes, S. P. Chem. Commun. 1997, 1035-1036. 6. Lowe, A. B.; Billingham, N. C.; Armes, S. P. Macromolecules 1998, 31, 5991-5998.7. Bütün, V.; Lowe, A. B.; Billingham, N. C.; Armes, S. P. J. Am. Chem. Soc. 1999, 121,

4288-4289.

Figure 5. FTIR spectra of (a) THPMA homopolymer, (b)PMAA obtained from the thermolysis of THPMA

homopolymer for 4 h, and (c) "PMAA" obtained from thethermolysis of THPMA homopolymer for 48 h. Theadditional band at 1820 cm-1 indicates methacrylic

anhydride formation

Synthesis of Multi-functional Initiators for the Productionof Block, Star and Functional Polymers

Ryan Edmonds,1 David Haddleton,1 Simon Harrisson,1 Kim Huan,1 FrançoisLecolley1

N

O

O

OH N

O

O

O

O Br

N

O

O

O

OBr

CO2Me

n MMA, CuBr,

N-propyl pyridylmethanimine

toluene, 90°C

Br

OBr

CH2Cl2, Et3N, 0°C

OH

OH

OH

OH

OOH

Br

BrO

O

O

O

O

OOO

Br OBr

O

Br

O

BrO

Br

+C6H5N / CCl3

80°C


1.Procedure, N-(2-bromoisobutyryloxy) succinimide

N-Hydroxysuccinimide (11.5 g, 0.1mol) was dissolved in anhydrous dichloromethane(250 mL, Note 1) with triethylamine (28.1 mL, 0.2 mol, Note 2) under nitrogen in a 500mL round-bottomed flask equipped with a magnetic stirrer. The flask was cooled to0°C in an ice bath before the dropwise addition of 2-bromoisobutyryl bromide (13.9mL, 0.11 mol). The mixture was stirred for 45 minutes and allowed to reach ambienttemperature. Subsequently the reaction mixture was poured into an excess of coldwater and extracted with diethyl ether (3 × 50 mL). The organic layer was washed witha saturated aqueous solution of Na2CO3 (3 × 50 mL), acidified water (pH = 4.5, 3 × 50mL), and again the saturated aqueous solution of Na2CO3 (3 × 50 mL). The organiclayer was dried over anhydrous MgSO4 and filtered. Finally the solvent was removedunder reduced pressure in order to isolate the title compound (22.4 g, yield 85%) as ayellowish solid.

2.Characterization, N-(2-bromoisobutyryloxy) succinimide

The compound melted in the range of 72-74°C. Elemental analysis returned C=36.35%; H = 3.82%; N = 5.03% and Br = 30.17%, compared to the calculated valuesfor C8H10NO4Br of C = 36.39%; H = 3.82%; N = 5.30% and Br 30.17%. The 300 MHz1H NMR spectrum (Note 3) in CDCl3 at ambient temperature shows absorptions fromthe succinimide ring at 2.87 ppm (s, 4H) and from the methyl groups of the 2-bromoisobutyryl moiety at 2.08 ppm (s, 6H). The 75 MHz 13C NMR spectrum in CDCl3at ambient temperature shows C=O peaks at 169.0 ppm (succinimide C=O) and 167.9ppm (isobutyryl C=O). Other peaks are observed at 26.03 (succinimide CH2), 31.09(C(CH3)2Br) and 51.60 (1C, C(CH3)2Br) ppm. The IR spectrum (Note 4) shows twoC=O stretches at 1772 (succinimide C=O) and 1728 (isobutyryl C=O) cm-1. The +EImass spectrum returned a major peak at m/z = 264 (M+), and minor peaks at 156,151, 149, 123, 121, 116, 115, 91, 87, 70 and 69.

3.Procedure, succinimide-functionalized poly(methyl methacrylate)

CuBr (0.134 g, 0.934 mmol) was placed in an oven-dried Schlenk tube. The tube wasfitted with a rubber septum, evacuated and flushed with dry N2 three times. Methylmethacrylate (3.7 mL, 34.6 mmol) and xylene (6.3 mL, Note 5) were transferred to thetube via degassed syringe. The mixture was stirred rapidly under nitrogen and N-propyl-2-pyridylmethanimine (0.408 g, 1.86 mmol) was added which imparted a deepred/brown colour to the solution. N-(2-bromoisobutyryloxy) succinimide (0.245 g, 0.934mmol) was added and the resulting solution was degassed by three freeze-pump-thawcycles. The mixture was placed in a thermostatically controlled oil bath at 90°C.Samples were taken periodically for conversion and molecular weight analysis.Conversion was measured gravimetrically by drying to constant weight in a vacuumoven at 70°C. After 2.5 h, 89% conversion had been reached, and the reaction wasexposed to air and allowed to cool to ambient temperature. The reaction mixture wasdiluted with 50 mL dichloromethane and passed down a short column of activated

Synthesis of Multi-functional Initiators . . .

basic alumina. Volatiles were removed under vacuum. The product was redissolved indichloromethane and precipitated from petroleum ether (40-60°C) to yield the polymeras a fine pale green powder. SEC analysis (Note 6) showed that the polymer had anumber-average molecular weight of 5800 g mol-1 and a PDi of 1.05.

4.Procedure, α,ω-bis(2-bromoisobutyrylethoxypropyl)-poly(dimethyl siloxane) Mn 5000 macroinitiator

α,ω-Bis(hydroxyethoxypropyl)-poly(dimethyl siloxane) (5.0 g, 0.91 mmol, Note 7) wasdissolved in anhydrous THF (400 mL) in an oven-dried nitrogen-flushed 500 mL roundbottom flask. Triethylamine (0.76 mL, 5.45 mmol) was added to the solution and wasallowed to stir to ensure mixing. 2-Bromoisobutyryl bromide (0.34 mL, 2.73 mmol) wasadded dropwise to the mixture, resulting in the formation of a white precipitate oftriethylammonium bromide (TEABr). The reaction was left to react at ambienttemperature for 14 h. The TEABr was removed by filtration and the THF was removedby rotary evaporation. The liquid products were dissolved in 400 mL ofdichloromethane and this solution was washed with 3 x 50 mL of saturated Na2CO3

solution. The dichloromethane layer was dried with MgSO4. After filtration, the solventwas removed under reduced pressure to give a pale yellow viscous liquid. The productwas placed in a vacuum oven at 60°C for 2 days to remove any traces of residualdichloromethane.

5.Characterization, α,ω-bis(2-bromoisobutyrylethoxypropyl)poly(dimethyl siloxane) Mn 5000 macroinitiator

The 300 MHz 1H NMR spectrum (Note 3) in CDCl3 at ambient temperature shows asinglet at 1.87 ppm (12H, C(CH3)2Br) confirming incorporation of the 2-bromoisobutyrylfunctionality. Signals from the ethoxy propyl linking groups are observed at 4.24 (t, 4H,J= 4.9 Hz, CO2CH2), 3.64 (t, 4H, J= 4.9 Hz, CH2CH2O), 3.35 (t, 4H, J= 6.9 Hz,OCH2CH2), 1.56 (m, 4H, CH2CH2CH2) and 0.55 ppm (m, 4H, CH2Si). The methylresonances from the poly(dimethyl siloxane) chain are observed at 0.00 ppm (m,400H, Si(CH3)2).

The 75 MHz 13C NMR spectrum in CDCl3 at ambient temperature shows peaks fromthe bromoisobutyryl groups at 170.6 (C=O), 55.6 (C(CH3)2Br) and 29.8 ppm (C(CH3)2),and from the linking groups at 73.1 (CO2CH2), 67.1 (OCH2CH2), 64.1 (CH2CH2O), 22.4(SiCH2) and 12.9 (SiCH2CH2) ppm. The poly(dimethyl siloxane) chain gives a broadpeak at 0.1 ppm (Si(CH3)2).

The IR spectrum (Note 4) shows alkyl C-H stretches at 2961 cm-1 and a C=O stretchat 1735 cm-1. Characteristic PDMS absorbances are observed at 1259 (Si(CH3)2) and1081-1012 cm-1 (Si-O).


6.Procedure, poly[(methyl methacrylate)-b-(dimethyl siloxane)-b-(methyl methacrylate)] ABA block copolymer

CuBr (0.104 g, 0.727 mmol) was placed in a dry Schlenk tube containing a magneticstirbar. The tube was evacuated and flushed with nitrogen three times. Methylmethacrylate (3.88 mL, 36 mmol), toluene (7.77 mL) and the difunctional poly(dimethylsiloxane) initiator (2.0 g, 0.36 mmol) were added to the Schlenk tube. The resultingsolution was degassed by three freeze-pump-thaw cycles and then placed in athermostated oil bath set to 90°C. Once the reaction temperature had been reached,N-propyl 2-pyridylmethanimine (0.23 mL, 1.46 mmol) was added, immediately causingthe reaction mixture to turn dark brown. The reaction was sampled periodically forconversion and molecular weight analysis. After 6 h, the reaction had reached 90%conversion and was cooled to ambient temperature, diluted with 50 mLdichloromethane and passed down a short column of activated basic alumina.Volatiles were removed under vacuum. The product was redissolved indichloromethane and precipitated into petroleum ether (40-60°C) to yield the polymeras a fine pale green powder.

7.Characterization, poly[(methyl methacrylate)-b-(dimethylsiloxane)-b-(methyl methacrylate)] ABA block copolymer

The 300 MHz 1H NMR spectrum (Note 3) in CDCl3 at ambient temperature showsbroad peaks characteristic of poly(methyl methacrylate) at 3.52 (CO2CH3), 2.00-1.67(backbone CH2) and 1.04-0.74 ppm (α-CH3), and poly(dimethyl siloxane) at 0.00 ppm(Si(CH3)2) from TMS. The molecular weight of the polymer was determined bycomparing this peak area of the methyl resonance at 3.52 (MMA blocks, 3H permonomer unit) with that of the Si(CH3)2 resonance at 0.00 ppm (DMS block, 6H perDMS unit). The degree of polymerization of the MMA block was then calculated fromthe known degree of polymerization of the DMS block (DPn = 67). This proceduregave a number average molecular weight (Mn) of 10 100 g mol-1 for the MMA portionsof the polymer, and an overall Mn of 15 600 g mol-1 for the total polymer.

Size exclusion chromatography (Note 6) returned a monomodal peak with a numberaverage molecular weight of 19 000 g mol-1 and polydispersity of 1.19 (Figure 1). Asthe chromatograph was calibrated using MMA standards, these results are onlyindicative of the true molecular weight distribution and value.

Thermogravimetric analysis of the copolymer (Note 8) showed a 14% weight loss at240°C, and a major weight loss between 350 and 400°C, corresponding to loss of thepoly(methyl methacrylate) blocks. The final weight loss between 500 and 600°C is dueto the decomposition of the poly(dimethyl siloxane) block. Differential scanningcalorimetry (Note 9) shows two distinct glass transitions, at –135°C and 107°C.These correspond to the poly(dimethyl siloxane) and poly(methyl methacrylate)blocks, respectively (Figure 2).


8.Procedure, 1,2,3,4,6-Penta-O-iso-butyryl bromide-α-D-glucose

A round-bottomed flask was flushed with nitrogen three times and charged with α-D-glucose (5 g, 27.8 mmol), 4-dimethylaminopyridine (0.1710 g, 1.4 mmol), anhydrouspyridine (30 mL) and anhydrous chloroform (50 mL). The solution was heated to 80°Cand 2-bromoisobutyryl bromide (20.75 mL, 168 mmol) was added dropwise. Themixture was then left to reflux overnight at 80°C under a nitrogen atmosphere, thencooled to 65°C and stirred for 3 days. The solution was subsequently diluted withdiethyl ether (50 mL) and washed with ice water (3 × 50 mL), 0.1M NaOH solution (3 ×50 mL) and water (3 × 50 mL), then dried over anhydrous MgSO4. The solvent wasremoved under vacuum and the crude product was recrystallized from methanol toyield white crystals in 81.3% yield (20.9 g).

9.Characterization, 1,2,3,4,6-Penta-O-iso-butyryl bromide-α-D-glucose

The melting point of the compound was 211°C. Elemental analysis returned C 33.6%,H 3.9%, compared to the calculated values for C26H37Br5O11 of C 33.76%; H 4.03%.The 400 MHz 1H NMR spectrum (Note 10) in CDCl3 at ambient temperature showsabsorptions from the sugar ring at 6.41 (d, 1H, J = 3.8 Hz) (anomeric C-H), 5.68 (t, 1H,J = 10.0 Hz, C3H), 5.33 (t, 1H, J = 10.0 Hz, C4H), 5.25 (dd, 1H, J1 = 3.8 Hz, J2 = 10.0Hz, C2H) and 4.37 ppm (overlapping peaks, 3H, C5H and C6H2) from TMS (Note 11).The methyl groups of the 2-bromoisobutyryl moieties return a broad peak between2.06 and 1.90 ppm (30H).

The 100 MHz 13C NMR spectrum in CDCl3 at ambient temperature shows a broadC=O peak at 170.4-169.6 ppm, peaks from the sugar backbone at 88.7 (anomeric C1),70.9 (C3), 70.6 (C5), 68.5 (C2), 68.2 (C4) and 61.9 (C6) ppm, and peaks from theisobutyryl functionality at 55.6-54.1 (-CBr(CH3)2), and 30.8-30.2 ppm (-CH3). The IRspectrum (Note 4) shows alkyl C-H stretches in the region of 3041-2838 cm-1 and astrong C=O stretch at 1738 cm-1. The +EI mass spectrum returned a peak at m/z =925 (M+).

10.Procedure, Five-arm star poly(methyl methacrylate) withglucose core

A Schlenk tube was charged with CuBr (71.7 mg, 0.5 mmol), 1,2,3,4,6-penta-O-iso-butyryl bromide-α-D-glucose (92.5 mg, 0.1 mmol), MMA (5.0 g, 50 mmol), and 5 mL oftoluene (Note 5). The resulting mixture was degassed by three freeze-pump-thawcycles. After this the Schlenk tube was heated to 90°C, and N-pentyl 2-pyridylmethanimine (0.19 mL, 1.0 mmol) was added by syringe. Samples for conversion andmolecular weight analysis were taken at intervals throughout the reaction. After 4 h,51% conversion was reached, and the solution was cooled to ambient temperatureand filtered over a bed of Celite (Note 12). The polymer was precipitated by adding the


solution dropwise to 100 mL of petroleum ether (40-60°C). After collection and dryingin air, the polymer was redissolved in CH2Cl2 and passed through a short column ofactivated basic alumina before reprecipitation into 100 mL petroleum ether (40-60°C)to produce a white polymer.

11.Characterization, Five arm star poly(methyl methacrylate) withglucose core

Conversions were measured by gravimetry. A sample was accurately weighed into apre-weighed aluminum pan. Volatile solvents and monomers were then removedunder vacuum at 60°C until constant sample weight was reached.

The conversion and molecular weight results thus obtained are shown in Table 1.Table 1. Conversion and molecular weight data for five arm star poly(methyl methacrylate) withglucose core.

Time (min) Conversion (%) Mn Theo (gmol-1)a

Mn

(g mol-1)b

PDi

30 14 7000 8880 1.1560 28 14000 14400 1.14

130 39 19500 21100 1.14180 43 21500 24500 1.13240 51 25500 27000 1.13

a Mn Theo = Conversion × [MMA]/[Initiator]. b Measured by size exclusion chromatography (Note 6)

12.Notes

1. Anhydrous solvents were obtained from BDH and used immediately on opening.2. Triethylamine was stored over NaOH pellets and filtered before use.3. A Bruker DPX300 NMR spectrometer was used.4. A Bruker Vector 22 FTIR spectrometer equipped with a Golden Gate diamond

attenuated total reflection (ATR) sample platform was used5. Solvents for polymerizations and methyl methacrylate were degassed before

use by sparging with N2.6. Molecular weight was measured by size-exclusion chromatography on a

Polymer Laboratories System using THF as the eluent at 1.0 mL/min andequipped with a PL autoinjector, a PL-gel 5 µm (50 × 7.5 mm) guard column,two PL-gel 5 µm (300 × 7.5 mm) mixed-C columns and a refractive indexdetector. The system was calibrated with narrow poly(methyl methacrylate)standards with peak weights ranging from 200 to 1.577 × 106 g mol-1, obtainedfrom Polymer Laboratories, except for MMA dimer, trimer and tetramer, whichwere prepared by catalytic chain transfer at the University of Warwick. Sampleswere prepared by dissolving the reaction mixture in THF to an approximatepolymer concentration of 4 mg/mL. The resulting solutions were passed througha short column of basic alumina to remove copper, then through a 0.2 µm filterbefore analysis.


7. Functionalized poly(dimethyl siloxane)s were purchased from ABCR Gelest andused as received.

8. A Perkin Elmer Nemesis 7 TGA was used.9. A Perkin Elmer Pyris 1 DSC was used.10.A Bruker DPX400 NMR spectrometer was used.11.Carbons are numbered from the anomeric carbon.12.The complex of copper bromide with N-pentyl-2-pyridylmethanimine is relatively

insoluble in toluene at ambient temperature, and precipitates from the reactionmixture on cooling.

13.Methods of Preparation

The reaction of 2-bromoisobutyryl bromide with an alcohol provides a simple syntheticroute to an enormous variety of initiators for living radical polymerization. The use ofpolymeric alcohols such as the poly(dimethyl siloxane)diol provides a route to di- andtriblock copolymers,2 while polyols such as saccharides3 and cyclodextrins4 may beused to produce star polymers with as many as 21 arms. The technique also allowsthe introduction of a wide range of functionalities into the molecule such ascholesterol3 and oligosaccharide5 groups. The use of bromopropionyl halides6,7

produces initiators more suitable for use with styrene or acrylate monomers anddifferent catalyst systems. An extensive review by Sawamoto et al.8 covers a widerange of functional initiators produced by this and other methods.

14.References

1. Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK2. Huan, K.; Bes, L.; Haddleton, D. M.; Khoshdel, E. J Pol Sci, Polym. Chem.

2001, 39, 1833,.3. Haddleton, D. M.; Edmonds, R.; Heming, A. M.; Kelly, E. J.; Kukulj, D. New

Journal of Chemistry 1999, 23, 477.4. Ohno, K.; Wong, B.; Haddleton, D. M. J Pol Sci, Polym. Chem. 2001, 39, 2206.5. Haddleton, D. M.; Ohno, K. Biomacromolecules 2000, 1, 152.6. Gaynor, S. G.; Matyjaszewski, K. Macromolecules 1997, 30, 4241.7. Jankova, K.; Chen, X.; Kops, J.; Batsberg, W. Macromolecules 1998, 31, 538.8. Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rev. 2001, 101, 3689.


Figure 1. Size exclusion chromatography traces for poly(dimethyl sulfoxide) macroinitiator(—) and triblock (PMMA-PDMS-PMMA) copolymer (- -).

11 12 13 14 15 16 17 18

-0.0010.0000.0010.0020.0030.0040.0050.0060.0070.0080.0090.0100.0110.0120.0130.014

PDMS Macroinitiator PMMA-PDMS-PMMA Copolymer

Elution Time / Minutes

Figure 2. Thermogravimetric analysis of PMMA-b-PDMS-b-PMMA triblock copolymer

0 100 200 300 400 500 600 700

0

20

40

60

80

100

Temperature (°C)

Wei

ght L

oss

(%)

Syntheses of Mikto Functional Initiators and Their Use inthe Preparation of Block, Miktoarm Star and Miktoarm

Star Block Copolymers Gurkan Hizal, Umit Tunca, Tuba Erdogan, Cigdem Celik, Zeynep Ozyurek

Department of Chemistry, Istanbul Technical University, Maslak, 34469, Istanbul,Turkey

Scheme 1


Synthesis of 2-phenyl-2-[(2,2,6,6-tetramethylpiperidino)oxy]-1-ethanol (1)

2-phenyl-2-[(2,2,6,6-tetramethylpiperidino)oxy]-1-ethanol was synthesized accordingto the modified procedure byof Hawker.1 To a solution of benzoyl peroxide (4.7 g,14.57 mmol) in distilled styrene (Merck 300 mL) was added 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) (3 g, 19.19 mmol) and the solution was heated to 90-95°Cunder nitrogen for 30 minutes. After cooling, the solution was redistilled under vacuumto dryness. The crude product was dissolved in ethylacetate and washed withaqueous 1% NaOH. The combined organic phases were dried over Na2SO4, filtered,evaporated and the residue was dissolved in dichloromethane (CH2Cl2). The productwas purified by column chromatography eluting with CH2Cl2, and 1-(Benzyl-oxy)-2-phenyl-2(2’,2’,6’,6’-tetramethyl-1-piperidinyloxy)-ethane (BST) was obtained as an oil.The product was further purified by recrystallization from cold hexane yielding whiteneedles (2.75 g, 38%).

In a 100 mL round-bottom flask, equipped with a magnetic stirrer, BST (2.75 g,7.21mmol) in 35 mL of ethanol and 8.5 mL of 0.2 N KOH(aq) were added and themixture was stirred until homogeneous, and the reaction mixture was heated to refluxunder nitrogen for 5 h. The solution was, then, concentrated to dryness. The reactionmixture was redissolved in CH2Cl2 (100 mL), washed with water (3X50 mL) andevaporated to dryness .The crude product was purified by column chromatography,eluting with 1:4 (hexane/dichloromethane) then gradually increasing to 1:9 (hexane/dicloromethane) to give the product 1 as pale yellow oil (1.62 g, 80%). 1H NMR(CDCl3) δ 1.15-1.58 (m,18H), 3.72 (d of d, J = 2.5 and 12 Hz, 1H, CH2), 4.22 (d of d, J= 9.5 and 12 Hz, 1H, CH2), 5.31 (d of d, J = 2.5 and 9.5 Hz, 1H, CH), 5.89 (br s, OH),7.29-7.36 (m, 5H, ArH). 13C NMR (CDCl3) δ 17.25, 20.66, 25.64, 32.20, 34.21, 39.99,40.52, 61.03, 67.93, 69.18, 84.23, 126.96, 127.83, 128.31, 139.10.

Synthesis of 2-phenyl-2-[(2,2,6,6- tetramethylpiperidino)oxy]ethyl2-bromo propanoate (2)2.

To a round bottom flask were added 1 (0.85 g, 3.06 mmol), triethylamine (Et3N, 0.7mL, 5 mmol), and 20 mL of dry tetrahydrofuran (THF). To the reaction mixture, stirredat 0°C under nitrogen, was added dropwise 2-bromo propanoyl bromide (0.53 ml, 5mmol) in 20 mL dry THF over a period of one hour. The reaction mixture was stirred atroom temperature overnight. The salt formed was removed by filtration and the solventTHF was evaporated. The crude product was dissolved in CH2Cl2 and washedsuccessively with dilute Na2CO3 aqueous solution and dried over anhydrous Na2SO4.CH2Cl2 was rotavapped and the crude ester was purified by preparative TLC (8 : 2hexane/ethyl acetate) to give 2 as a pale yellow oil (0.52 g, 41%). The compound 2was characterized by 1H and 13C NMR (Note 1). 1H NMR spectrum of initiator showed

Syntheses of Mikto Functional Initiators

no signal corresponding to OH protons of the starting material 1, indicatingquantitative esterification. 1H NMR (CDCl3) δ 0.72-1.60 (m, 18H), 1.68 (d, J = 6.9 Hz,3H, CH-CH3), 4.25 (q, J = 6.9 Hz, 1H, CH-CH3), 4.41 (m, 1H, CHH), 4.64 (m, 1H,CHH), 4.95 (m, 1H, CH), 7.28-7.32 (m, 5H, ArH); 13C NMR (CDCl3) δ 17.20, 20.45,21.66, 22.14, 34.06, 39.96, 40.09, 40.55, 60.19, 67.48, 83.72, 127.75, 128.06, 128.28,129.61, 132.76, 140.20, 169.83.

Synthesis of Poly(tert-butyl acrylate) (PtBA) macroinitiator (PI)3.

Poly(tert-butyl acrylate) (PtBA) macroinitiator, P I was prepared by atom transferradical polymerization (ATRP) of tert-butylacrylate (tBA) in bulk usingCuBr/N’,N’,N,N’’,N’’-pentamethyldiethylentriamine (PMDETA) as catalyst and 2 as aninitiator at 80oC. To a Schlenk tube equipped with magnetic stirring bar, the degassedmonomer (3 mL, 20.48 mmol), PMDETA (0.0214 mL, 0.102 mmol), CuBr (0.0146 g,0.102 mmol), initiator (0.0422 g, 0.102 mmol) were added in the order mentioned. Thetube was degassed by three freeze-pump-thaw cycles, left under vacuum and placedin a thermostated oil bath. After 5.5h polymerization, the reaction mixture was diluted

Scheme 2


with THF and then passed through a column of neutral alumina to remove the metalsalt. The excess of THF and unreacted monomer were evaporated under reducedpressure. The resulting polymer was dissolved in THF, precipitated intomethanol/water (80/20; v/v). After filtration, the polymer was dissolved in a minimumamount of dichloromethane (approximately 30 mL) and dried over Na2SO4,dichloromethane was then removed by evaporation. The conversion was calculatedgravimetrically. The number average molecular weight of the polymer determined byGPC (Note 2) and it is given in Table 1.

Synthesis of Polystyrene (PSt) macroinitiator (P IV)3.

Polystyrene (PSt) macroinitiator P IV was prepared by stable free radicalpolymerization (SFRP) of styrene (St) (3 mL, 26.183 mmol) in the presence of 2(0.108 g, 0.262 mmol). The reaction mixture was degassed by three freeze-pump-thaw cycles and polymerized at 125°C for 18h. The polymerization mixture was dilutedwith THF and the polymer was precipitated into methanol. The theoretical molecularweight of the polymer was calculated from Mn, theo= [M]o/[I]ox conv. % x Mw, monomer +Mw, initiator.

Synthesis of poly(tBA-b-MMA) (P II) diblock copolymer using PtBA(P I) as a macroinitiator.

The procedure for the synthesis of diblock copolymer P II is as follows: thepolymerization of methyl methacrylate (MMA) was carried out in a Schlenk tubeequipped with a magnetic stirring bar. MMA (3 mL, 28.046 mmol), PMDETA (0.0059mL, 0.028 mmol), CuCl (0.0028 g, 0.028 mmol), diphenylether (DPE) (MMA/DPE = 1;v/v) and macroinitiator P I (0.51 g, 0.028 mmol) were added to the tube respectively.The tube was then subjected to freeze-pump-thaw cycles three times. Thepolymerization was conducted at 80°C for 19 h. After the polymerization, the reactionmixture was diluted with THF and then passed through a column of neutral alumina toremove the metal salt. The excess of THF and unreacted monomer was evaporatedunder reduced pressure. The resulting polymer was dissolved in THF, precipitated into10 fold excess methanol/water (80/20; v/v) and then filtered. The composition of blockcopolymer was elucidated by 1H NMR measurement (Note 1). The 1H NMR spectrumof poly (tBA-b-MMA) block copolymer exhibit the major peaks which are characteristicof the polymerized tert-butyl acrylate and methyl methacrylate segments. Themolecular weights were calculated from the integration of peaks at 1.43 ppm (C(CH)3)of tBA to 3.58 ppm (-OCH3) of MMA (Note 1).


Synthesis of poly(St-b-tBA) (PV) diblock copolymer usingpolystyrene (P IV) as a macroinitiator.

Poly(St-b-tBA) block copolymer, P V, was prepared by ATRP of tBA (3 mL, 20.48mmol) using PMDETA (0.00143 mL, 0.0683 mmol), CuBr (0.0098 g, 0.0683 mmol)and macroinitiator P IV (0.307 g, 0.0683 mmol). The polymerization was carried out at80°C under degassed condition for 3.5 h. The purification was carried out asdescribed above for the diblock copolymers. The composition and molecular weight ofdiblock copolymer were determined via 1H NMR measurement.

Synthesis of poly(St-b-tBA-b-MMA) triblock copolymers (P III, P VI).

Triblock copolymer, P III, was obtained by SFRP of St (0.67 mL, 5.848 mmol) usingDPE as solvent (monomer/solvent = 1; v/v) and a macroinitiator, P II (0.598 g, 0.00824mmol). The reaction mixture was degassed and polymerized at 125°C for 46h. Thepolymerization mixture was diluted with THF and precipitated into 10 fold excessmethanol. Integratiion of the peaks between 6.5-7.0 ppm of PSt (aromatic protons)and 3.58 ppm of PMMA (OCH3) allowed us to calculate the composition of triblockcopolymer.

Triblock copolymer, P VI, possessing same monomer structure was achieved byATRP of MMA (2 mL, 18.698 mmol) using PMDETA (0.0033 mL, 0.0156 mmol), CuCl(0.00154 g, 0.0156 mmol), DPE (monomer/solvent = 0.5; v/v) and macroinitiator, P V(0.5 g, 0.0156 mmol) under degassed condition at 80°C for 4 h. The polymer wasisolated and purified as described above for the diblock copolymers.


Run Monomer [M]o Initiator Conv. Mn,theog Mn,GPC

h Mn,NMR Composition 1H NMR

MW/Mn

mol L-1 (%)

PIa tBA 6.83 1 76 19400 18200 - 1,10PIIb MMA 4.67 PI 54 72200 68000 72600 27% PtBA, 73% PMMA 1,13PIIIc St 4.36 PIII 60 117000 68000 123400 41% PSt, 16% PtBA, 43% PMMA 1,30PIVd St 8.73 1 40 4200 4500 - 1,21PVe tBA 6.83 PIV 68 30400 27200 32000 13% PSt, 87% PtBA 1,15

PVIf MMA 3.12 PV 23 59600 50000 61000 7% PSt, 46% PtBA, 47% PMMA 1,12

Table 1. Syntheses of ABC triblock copolymers via ATRP-ATRP-SFRP and SFRP-ATRP-ATRP routes.

a) [M]o:[I]o:[CuBr]o:[PMDETA]o=200:1:1:1.b) [M]o:[I]o:[CuCl]o:[PMDETA]o =1000:1:1:1, (MMA/DPE=1, v/v) c) [M]o:[I]o =710 (St/DPE=1, v/v). d) [M]o:[I]o =100. e) [M]o:[I]o:[CuBr]o:[PMDETA]o=300:1:1:1. f) [M]o:[I]o:[CuCl]o:[PMDETA]o=1200:1:1:1 g) Mn, theo= [M]o/[I]ox conv. % x Mw (monomer) + Mn, initiator. h) Molecular weights were calculated by the aid of linear polystyrene standards (Note 2).

Scheme 3.


Synthesis of 2,2-bis[methyl (2-bromo propionato]propionic acid (4).4

2,2-bis(hydroxymethyl)propionic acid (3) (5g, 37 mmol) was dissolved in 80 mL of dryTHF. To this solution, triethylamine (12.5 mL, 89 mmol) was added and the solutionwas cooled to 0 oC. 2-bromopropionyl bromide (9.5 mL, 89 mmol) in 15 mL of THFwas added to the solution in 1h. The reaction mixture was stirred overnight at roomtemperature. The solution was, then, filtered and the solvent was evaporated undervacuum to give 4 as a pale yellow oil (10.89 g, 78%).

Synthesis of 2,2-bis[methyl (2-bromopropionato)]propionyl chloride (5).4

In a flask equipped with magnetic stirrer, 2,2-bis[methyl (2-bromo propionato]propionicacid, 4 (5 g, 12 mmol) and 50 mL of benzene were added and the solution was stirreduntil clear. Then phosphoruspentachloride (PCl5) (3g, 14 mmol) was added and thesolution was stirred overnight at room temperature. The solution was filtered andbenzene was removed by evaporation. The product was washed with hexane toremove the excess of PCl5. The organic phase was evaporated to yield 2.74 g ofbrown oil.

Scheme 4


Synthesis of 2-phenyl-2-[(2,2,6,6-tetramethyl)-1-piperidinyloxy] ethyl2,2-bis[methyl(2-bromopropionato)] propionate (6)4.

To a round-bottom flask were added 2-phenyl-2-[(2,2,6,6-tetramethylpiperidino)oxy]-1-ethanol,1 (1.2 g, 4.32 mmol), Et3N (1 mL, 7.16 mmol), and 20 mL of dry THF. To thereaction mixture stirred at 0-5°C 2,2-bis[methyl(2-bromopropionato)propionyl chloride,5 (2.7 g, 6.39 mmol) in 10 mL of dry THF was added dropwise over a period of half anhour. The reaction mixture was stirred at room temperature overnight. The by-productsalt was removed by filtration and solvent was evaporated. The crude product wasdissolved in CH2Cl2 and washed two times with Na2CO3 aqueous solution and oncewith water, respectively. The organic phase was dried over anhydrous Na2SO4 and thecrude ester was purified by column chromatography (silica gel, 1:1 hexane/ CH2Cl2 asan eluent) to give the dual initiator, 6 as pale yellow oil (2.41 g; 62%). The compound6 was characterized by 1H and 13C NMR (Note 1). 1H NMR (CDCl3): δ 7.26-7.32 (m,5H, ArH), 4.92 (m, 1H, ArCH), 4.55 (m, 1H, ArCHCHH), 4.0-4.5 (m, 7H, ArCHCHH,CH2OCO, and CHC(CH3)Br), 1.77 (d, 6H, C(CH3)Br), 0.74-1.58 (m, 18H).

13C NMR (CDCl3) δ 174.0; 169.5; 140.0; 128.3; 128.2; 127.4; 128.2; 83.8; 66.7; 66.2;66.0; 65.9; 60.0; 48.4; 46.4; 40.1; 39.5; 34.0; 28.8; 21.4-21.6; 20.5; 17.20-17.80.


Synthesis of polystyrene (PSt) precursors (PVII).

The monomer (St) (3 mL, 26.183 mmol) and the trifunctional initiator 6 (0.0579 g,0.087 mmol) were placed in a Schlenk tube. The reaction mixture was degassed bythree freeze-pump-thaw cycles, left under vacuum, placed in an oil bath at 125°C andstirred for 28 h. The polymerization mixture was diluted with THF, precipitated intomethanol, filtered and dried in vacuum at room temperature.

Scheme 5


Synthesis of (PSt)(PtBA)2 miktoarm star polymer (PVIII).

Into a Schlenk tube equipped with a magnetic stirring bar, tBA (3.662 mL, 25 mmol),PMDETA (0.0948 mL, 0.045 mmol), CuBr (0.0065 g, 0.045 mmol) and PStmacroinitiator PVII (0.3 g, 0.0227 mmol) were added respectively. The solution wasdegassed by three freeze-pump-thaw cycles, left under vacuum. The reaction washeated to 80oC in an oil bath for 9 h. After diluting with THF, the reaction mixture waspassed through neutral alumina column to remove the metal salt. The excess THFand the unreacted monomer were evaporated under reduced pressure. The polymerwas dissolved in THF, precipitated into methanol/H2O (80/20; v/v), isolated, and driedovernight in vacuum at 50°C. 1H NMR spectrum of (PSt)(PtBA)2 exhibits major peakswhich are characteristic of the PSt and PtBA. Integrating the peaks between 6.5-7.0(aromatic protons) and 1.43 ppm (tert-butyl groups) allowed us to calculate thecomposition of miktoarm star polymer, (26% PSt, 74% PtBA).

Synthesis of (PSt)(PtBA)2(PMMA)2 miktoarm star block copolymer(P IX).

Into a Schlenk tube MMA (0.282 mL, 2.64 mmol), CuCl (0.0008 g, 0.0081 mmol),PMDETA (0.0184 mL, 0.0088 mmol), DPE (MMA/DPE =1; v/v) and the macroinitiatorPVIII (0.2 g, 0.0044 mmol) were added in the given order. The mixture was degassedand polymerized at 80°C for 4 h. After dilution with THF, the polymer was recoveredas mentioned above. The composition and the molecular weight of miktoarm starblocks were elucidated by 1H NMR through the integration of aromatic (6.5-7.0 ppm)and OCH3 (3.58 ppm) protons, (10% PSt, 28% PtBA, 62% PMMA).

Scheme 6

Synthesis of miktofunctional initiator (7).5

2,2-Bis[methyl(2-bromopropianato)propionyl chloride 5 (5.53 g, 13.08 mmol) wasadded into molar excess (25 times) of ethylene glycol (18.26 mL) and reacted for 21 hat 0 oC, in a jacketed Schlenk tube. The reaction mixture was dissolved in water andextracted with CH2Cl2. The organic phase was washed with saturated aqueoussolution of NaHCO3, followed by water and dried over Na2SO4. After filtration, the


solvent was distilled off under reduced pressure and orange-like color oil wascollected in 40% yield (2.3 g). The 1H NMR spectrum of compound 7 (Note1) showsthe peaks of the ethylene glycol segment (HO-CH2: 2.2 and 3.81 ppm) together withthe peaks of the 2-bromopropanoate groups (CH(CH3)Br: 4.50-4.18 and 1.79 ppm). 1HNMR (CDCl3): δ 4.50-4.18 (m, 8H, CH2OCO, CH(CH3)Br, HOCH2CH2OCO), 3.81 (t,2H, HOCH2CH2OCO), 2.2 (bs, 1H, HOCH2), 1.79 (d, 6H, CH(CH3)Br), 1.31 (s, 3H,CCH3).Scheme 7

Scheme 7.


Synthesis of PCL Macroinitiator by ROP (PX) PCL macroinitiator was prepared by the ROP of ε-caprolactone (CL) in bulk usingSn(Oct)2 as a catalyst and 2 as an initiator at 110°C for 64 h. To a previously flamedSchlenk tube equipped with a magnetic stirring bar, the degassed monomer CL (3,91mL, 36.86 mmol), catalyst (0.001 mL, 0.0031 mmol) and initiator (0.5 g, 0.922 mmol)were added in the order mentioned. The tube was degassed by three freeze-pump-thaw cycles, left under vacuum and placed in a thermostated oil bath. After thepolymerization, the resulting polymer was dissolved in THF, precipitated into excessmethanol and then isolated. The molecular weight was calculated with the aid ofpolystyrene standards by using an equation (MPCL= 0.259 X MPSt

1.073). The Mn, NMRvalue was determined from the ratio of integrated peak areas of -CH2O (4.0 ppm) andthe initiator peaks around 4.3 ppm.

Synthesis of AB2 Miktoarm Star Polymer by ATRP (PXI)

The synthesis of PCL-(PtBA)2 miktoarm star polymer was accomplished by the ATRPof tBA ( 2.82 mL, 19.23 mmol) in bulk using PMDETA (0.032 mL, 0.154 mmol) CuBr(0.022 g, 0.154 mmol) and macroinitiator PXI (0.25 g, 0.0769 mmol). Thepolymerization was carried out at 100°C under degassed conditions for 4 h. After thepolymerization, the reaction mixture was diluted with THF and then passed through acolumn of neutral alumina to remove the metal salt. The excess THF and theunreacted monomer were evaporated under reduced pressure. The resulting polymerwas dissolved in THF and precipitated into methanol/ water (80/20; v/v). After filtration,the polymer was dissolved in minimum amount of CH2Cl2, dried over Na2SO4 and thesolvent was removed by evaporation. The theoretical Mn value of PCL-(PtBA)2 wascalculated according to Mn,theo = ([M]0/[I]0) X Conv. X 128.17 + Mn,NMR of PCLprecursor and the molecular weight (Mn,NMR) was determined from the integration ofsignals appeared at 1.41 ppm (-C(CH)3) of tBA to 4.01- 4.06 ppm (-CH2O) of CL.

Notes

1. The 1H NMR and 13C NMR spectra were recorded on a Bruker Spectrometer (250MHz for 1H NMR and 62.86 MHz for 13C NMR) in CDCl3.

2. Gel permeation chromatography (GPC) measurements were carried out with anAgilent model 1100 instrument consisting of pump and refractive-index and UVdetectors and four Waters Styragel columns (HR 5E, HR 4E, HR 3, and HR 2). THFwas used as eluent at a flow rate of 0.3 mL/min at 30°C. The molecular weight of thepolymers was calculated with the aid of polystyrene standards (Polymer Laboratories).


References

1. Hawker, C.J.; Barclay, G.G.; Orellana, A.; Dao, J.; Devonport, W.Macromolecules 1996, 29, 5245.

2. Tunca, U.; Karlıga, B.; Ertekin, S.; Ugur, A. L.; Sirkecioglu, O.; Hizal, G. Polymer2000, 42, 8489.

3. Tunca, U.; Erdogan, T.; Hizal, G. J Polym Sci Part A: Polym Chem 2002, 40,2025.

4. Celik, C.; Hizal, G.; Tunca, U. J Polym Sci Part A: Polym Chem 2003, 41, 2542.5. Erdogan, T.; Ozyurek, Z.; Hizal, G.; Tunca, U. J Polym Sci Part A: Polym Chem

2004, in press.

Four-Arm Star Polymers Using Atom Transfer RadicalPolymerization

Submitted by: B. S. Shemper and Lon J. Mathias1

Br O

Br+

HO OH

HO OHEt3N

O O

O O

OBr

O Br

OBr

Br O

DMAPTHF

T=0ºC

PPGM or MPEGMAO O

O O

O

O

O

O BrO

O

O Hn

mBr

OO

OHn

m

BrO

O

OR

R'n

mBr

OO

O Hn

m

CuBr/PMDETA

MEK, 80 ºC

R = CH3 or H

R ' = H or CH3

STARINITIATOR

Zonyl TMO O

O O

O

O

O

O BrmBrm

BrO

O

mBr

OO

mCuBr/PMDETA

Benzene/TFT, 114 ºC

(F2C)7

CF3

(CF2)7F3C

OO

(CF2)7F3C

OO

(F2C)7CF3

STARINITIATOR


The syntheses of the star macroinitiator and the 4-arm star polymer of poly(propyleneglycol) methacrylate (PPGM) were first described by Shemper, Acar, and Mathias.2

The same reaction conditions were used here for the synthesis of the star polymer ofmethyl ether poly(ethylene glycol) methacrylate (MPEGMA), and also modified for thepolymerization of the fluorinated monomer 1H,1H,2H,2H-heptadecafluorodecylmethacrylate (Zonyl TM®) to produce a final product with star architecture.

1.Procedure

a. Star macroinitiator (Note 1)

Pentaerythritol (56 mmol, 7.62 g) (Note 2), tetrahydrofuran, triethylamine (56 mmol,7.8 mL) and 4-(dimethylamino)pyridine (DMAP) (11 mmol, 1.34 g) are placed into athree-necked round-bottom flask fitted with a condenser and an addition funnel. Themixture is cooled to 0 °C. 2-Bromoisobutyryl bromide (224 mmol, 27.7 mL) is dilutedwith THF (1:1 v/v) in a separate flask (under nitrogen), transferred to the additionfunnel and added to the main reaction flask dropwise (Note 3). The solution is kept at0 °C for 5 h. An excess of 2-bromoisobutyryl bromide (22.4 mmol, 2.8 mL) was thenadded to the reaction mixture and the solution was brought to room temperature andstirred overnight under nitrogen. When the reaction was complete (Note 4), themixture was filtered, taken up in CH2Cl2 and then extracted with water, 0.5 N HCl,NaHCO3, water (3x) and brine. The organic layer was dried over Na2SO4, filtered andthe solvent evaporated to give product in ca 60 % yield; mp 134 °C (Note 5). 13C NMR(CDCl3, 300 MHz, Note 6): δ= 170.86, 62.86, 55.17, 43.63, 30.62. 1H NMR (CDCl3,300 MHz, Note 6): δ= 1.94, 4.33. The lack of extraneous peaks and the expectedintegration values of the peaks observed in the 1H NMR spectrum of this compoundconfirm purity of >95 % for this compound.

b. Polymerization of star polymers of PPGM and MPEGMA

The polymerizations of PPGM and MPEGMA were conducted in a dried three-neckedround-bottom flask (Note 7) using MEK as the solvent. The reaction flask was sealedwith rubber septa and maintained under an atmosphere of nitrogen (Note 8). Allreactants were degassed before being added to the flask and the final solution waspurged with nitrogen for 30 min before addition of the ligand. (Note 9) Reactions werecarried out in an oil bath regulated at 80 °C by adjusting the setting of a stirring hotplate. The resulting polymers were precipitated into hexanes and dried in a vacuumoven overnight (Note 10). Removal of the catalyst was achieved by passing a polymersolution through alumina column, using chloroform as the solvent. Excess solventwas removed using a rotatory evaporator. The colorless solution obtained was thenprecipitated into hexanes, and the solid obtained dried in a vacuum oven overnight.The monomer conversion was determined gravimetrically. In a typical procedure, thestar initiator (0.625 mmol, 0.4575 g) and copper(I) bromide catalyst (0.625 mmol,0.089 g) were added to a previously dried three-necked round-bottom flask and

Four-Arm Star Polymers

nitrogen was purged through the septum-sealed flask for 30 minutes. Maintaining thenitrogen purge during and between additions, the monomer MPEGMA (20 mmol, 5mL) was added to the flask using a syringe which had also been purged with nitrogen(3x). Solvent MEK (20 mL) was added last (Notes 11 and 12). The system was placedin an oil bath at 80 °C (Note 13). The ligand PMDETA was then added (0.625 mmol,130 µL) through the use of a syringe (Note 14). The reaction was allowed to proceedfor 3 h, after which the temperature of the flask was cooled to ambient temperatureand the solution was precipitated into hexanes. The precipitate was dried in a vacuumoven for 48 h (Note 15). The dried material was dissolved in chloroform and thissolution passed through a column packed with basic alumina and wetted withchloroform to remove the catalyst. Excess solvent was removed using a rotaryevaporator. The concentrated polymer solution was precipitated into hexanes anddried in vacuum oven before polymer characterization. The 13C NMR spectra for thestar polymers of PPGM and MPEGMA are shown in Figure 1 and 2. Molecularweights were obtained by size exclusion chromatography (SEC) (Note 16).

c. Synthesis of four-arm star fluorinated polymer, poly(1H,1H,2H,2H-heptadecafluorodecyl methacrylate)

The polymerization of 1H,1H,2H,2H-heptadecafluorodecyl methacrylate (Zonyl TM®)was conducted in a dried three-necked round-bottom flask using a mixture of benzeneand trifluorotoluene (50:50 v/v) as solvent (Note 17). In a typical procedure, the starinitiator (0.75 mmol, 0.549 g) and copper(I) bromide (0.75 mmol, 0.107 g) were addedto the previously dried flask. The flask was attached to a degassed reflux condenserwith septa gas inlets and outlets and purged with nitrogen for 30 min. Maintaining thenitrogen purge during and between additions, the monomer 1H,1H,2H,2H-heptadecafluorodecyl methacrylate (15 mmol, 5 mL) was added to the flask using asyringe which had been previously purged with nitrogen (3x). The mixture of benzeneand TFT (20 mL) was added and the flask was placed in an oil bath at 114 °C. Theligand PMDETA was then added (0.75 mmol, 156 µL) via a nitrogen-purged syringe.An atmosphere of argon was introduced and the reaction was allowed to proceed for 3h. After cooling to ambient temperature, the reaction mixture was precipitated intoether; the precipitate was collected on vacuum filtration on a fritted glass filter anddried in a vacuum oven for 6 h (Note 18). The solid polymer was characterized by 13CNMR spectroscopy for estimation of its molecular weight (Note 19).

2. Notes

1. Pentaerythritol (Aldrich, 98%), triethylamine (Aldrich, 99%), 2-bromoisobutyrylbromide (Aldrich, 98%), 4-(dimethylamino)pyridine (Aldrich, 99%), poly(ethyleneglycol) methyl ether methacrylate (Aldrich, molecular weight = 268.2 g/mole,estimated by 1H NMR), methyl ethyl ketone (MEK) (Fisher), ethyl 2-bromoisobutyrate (BriB) (Aldrich, 98%), copper(I) bromide (Aldrich, 99.999%), and


N,N,N’,N’,N”-pentamethyl-diethylenetriamine (PMDETA) (Aldrich, 99%) were usedas received. Tetrahydrofuran (THF) was purified by distillation from CaH2.

2. Pentaerytritol was not fully added to the flask at once. Instead, smallportions of pentaerythritol were added over time, starting with 0.2equivalents and followed by 0.2 equivalents every 1 h. The septum wasremoved, the solid added, and the septum was quickly replaced.

3. The slow dropwise addition facilitates the formation of triethylamine saltprecipitate during the reaction under vigorous stirring.

4. Completion of reaction was monitored by thin layer chromatography anddetected after 16 hours of reaction.

5. The melting point of this compound was obtained by differential scanningcalorimetry (DSC). DSC scans were taken at a heating rate of 10 °C/min undernitrogen, to a temperature corresponding to 30 °C below the temperature at which5% weight loss occurs (ca 175 °C), then cooled to room temperature andrescanned at the same heating rate. The mp value was recorded from the second-scan data for the same sample.

6. 1H NMR and 13C NMR spectra were recorded on a Varian UNITY INOVA 500 atroom temperature using CDCl3 with TMS as an internal reference.

7. All glassware, needles and stirring bars were dried overnight in an oven at150 °C and purged with nitrogen before use.

8. All three necks were capped with rubber septa. Nitrogen flow was achievedby inserting one syringe needle connected to a nitrogen line in one septumand attaching a second needle to another septum that served as an outlet.A bubbler was used to monitor nitrogen flow through the line.

9. Common initiators used in ATRP reactions are usually liquids, as forexample, ethyl-2-bromoisobutyrate (BriB). Therefore, their addition to themain reaction flask as the last step carried out in the procedure is trivial.However, the star macroinitiator used here is a solid. In this case, there aretwo options for the addition of the initiator to the system. The first oneconsists of dissolving the initiator in the solvent or mixture of solvents usedin the reaction procedure, followed by purging of the solution, before addingit into the system containing catalyst, monomer, solvent and ligand. Thesecond method, which was chosen here, consists of adding the initiator tothe flask first, followed by catalyst, monomer and solvent in that order. Theligand (liquid PMDETA) is added as the last step. Nitrogen purge during thisprocess is of extreme importance.

10.For kinetic experiments, samples were taken at regular intervals using a syringeand precipitated into hexanes.

11.It must be noted that monomers and solvents were always degassed withnitrogen for at least 2 h before addition to the reaction flask. The ratio ofmonomers to solvents was kept at 20% (v/v) in all the reactions describedhere.

12.The final molecular weight of a polymer synthesized via living radicalpolymerization using the ATRP mechanism can be estimated according tothe equation below.

Mn calc = (([M]/[I] x MWmonomer) x conversion) + MWstar initiator


Therefore, the quantity of monomer used in the reaction is defined based on thetarget molecular weight desired. For the procedure given here, the molecularweight of the monomer MPEGMA was 262.8 g/mol as estimated using 1H NMRspectroscopy, the target molecular weight was 9141 g/mol for a final overall DP of32 (approximately 8 monomer units per arm) calculated for 100% conversion.

13.Heating the whole system up to the reaction temperature, before theaddition of the ligand PMDETA, allows better homogenization of the mixture.This procedure is useful when initiator is added in the last step.

14.It is interesting to observe the change in color of the entire system.Typically, the reactions carried out in MEK were green before addition of theligand. Immediately after addition, the mixture turns blue. As thepolymerization progresses to higher conversion, the system is characterizedby a dark green color. Reactions carried out in a mixture of benzene andtoluene, as for fluorinated polymers, were light green before ligand addition,turned dark murky green immediately after, and at the end of the reaction,had a dark caramel coloration.

15.At this point monomer conversion may be gravimetrically determined.16.Molecular weight and molecular weight distributions were measured using size

exclusion chromatography (SEC). The syntheses of star polymers with lowdegrees of polymerization were performed to overcome inconsistencies ofmolecular weight values obtained by different characterization techniques causedby the smaller hydrodynamic volume of star polymers. The molecular weight of thestar PPGM polymer with low DP was 10.1 x 103 g/mol as estimated by SEC and10.6 x 103 g/mol according to quantitative integration of the quaternary carbons ofthe polymer backbone (at δ = 44.7 ppm) and the dimethyl substituted quaternarycarbon of the star initiator (at δ = 41.5 ppm), identified in the 13C NMR spectrum ofthis compound. The identification and integration of polymer backbone and starinitiator quaternary carbons using 13C NMR spectroscopy facilitated the estimationof the molecular weights of all star polymers synthesized here. For instance, the13C NMR spectrum of the star MPEGMA is shown in Figure 2 and the resonancesof quaternary carbons of the polymer backbone and the star initiator can be seenat around 45 and 42 ppm, respectively. Molecular weight estimated by NMR was9.1 x 103 g/mol and that determined by SEC was 8.1 x 103 g/mol.

17.The use of a mixture of benzene and TFT has also been reported by Kim et al. forthe synthesis of linear polymers of fluorooctyl methacrylates via copper-mediatedliving radical polymerization.3

18.The fluorinated polymers were not soluble in any common organic solvents butdissolved in highly fluorinated solvents such as 1,1,1,3,3,3-hexafluoroisopropanol(HFIP) or α,α,α-trifluorotoluene (TFT). The final polymer sample was stirredvigorously in hot chloroform and then allowed to phase separate. The chloroformlayer containing most of the green color associated with the catalyst was thensiphoned off. Repeated washing in this manner, followed by high vacuumevaporation and cooling, yielded a sticky, creamy colored, solid.

19. The clean fluorinated star polymer was soluble in TFT and 13C NMR spectroscopyof the solution was possible with the use of a D2O capillary insert (Figure 3). Due toinsolubility of the fluorinated polymers in common organic solvents, determinationof molecular weight by SEC is difficult. Hence, quantitative 13C NMR spectroscopy


was used as the characterization technique to estimate final molecular weight ofpolymers as described in Note 16. The molecular weight estimated this way was8.2 x 103 g/mol.

3.Characterization

Molecular weight and molecular weight distributions were measured using sizeexclusion chromatography (SEC) on a system equipped with four styrene gel mixed-bed columns (7.5 mm id × 300 nm, 10 µm particle diameter, American PolymerStandard Corporation, Mentor, OH) using tetrahydrofuran (THF) as eluent.Polystyrene standards were used for calibration. 1H NMR and 13C NMR spectra wererecorded on a Varian UNITY INOVA 500 at room temperature using CDCl3 with TMSas an internal reference. Differential scanning calorimetry (DSC) scans were run on aTA Instruments 2920, controlled by Thermal Analyst 2100. Scans were taken at aheating rate of 10 °C/min under nitrogen.

4.Discussion

The use of multifunctional star initiators for ATRP reactions have also been reportedby others.4,5 Moschogianni, Pispas and Hadjichristidis4 used a tetrakisbromomethylbenzene to initiate the polymerization of MMA while Kraus and Robello5 used amultifunctional sulfonyl chloride to polymerize MMA via ATRP.

Star-shaped amphiphilic polymers were also synthesized by An and Cho6 through theuse of a hydrophilic four-arm PEG macroinitiator and polystyrene as the hydrophobiccomponent. Francis et al.7 designed asymmetric and miktoarm star polymers by usingthe ATRP mechanism to synthesize one arm of the star polymer, followed by chemicalmodification of the terminal group of the polymer obtained to create new ATRPinitiating sites for formation of extra arms. Moreover, three-arm star polymers werealso successfully synthesized by Hong et al.8 via ATRP in the presence of a hybridcatalyst system composed of a CuBr/4,4’-dimethyl-2,2’-bipyridine compleximmobilized on a polystyrene bead combined with the soluble catalystCuBr/Me6TREN.


Figure 1. 13C NMR spectrum of PPGM star polymer

OO Br

OO

O Hn

m

C

4

a

bc

de

f g

d

e

-250255075100125150175200225

a + g

bcf

C

O

OBr

OO

O3.7

4

n

Figure 2. Expanded 48-40 ppm region of 13C NMR spectrum of MPEGMA star polymer


5.References

1. School of Polymers and High Performance Materials, University of SouthernMississippi, Box 10076, Hattiesburg, MS 39406-0076.

2. Shemper, B. S.; Acar, A. E.; Mathias, L. J. J. Polym. Sci., Polym. Chem. Ed. 2002, 40,334.

3. Lim, K. T.; Lee, M. Y.; Moon, M. J.; Lee, G. D.; Hong, S.; Dickson, J. L.;Johnston, K. P. Polymer 2002, 43, 7043.

4. Moschogianni, P.; Pispas, S.; Hadjichristidis, N. J. Polym. Sci., Polym. Chem. Ed. 200139, 650.

5. Kraus, A.; Robello, D. R. Polymer Preprints 1999, 40(2), 431.6. An, S. G.; Cho, C. G. Polymer Preprints 2002, 43(2), 259.7. Francis, R.; Lepoittevin, B.; Taton, D.; Gnanou, Y. Macromolecules 2002, 35,

9001.8. Hong, S. C.; Neugebauer, D.; Inoue, Y.; Lutz, J.; Matyjaszewski, K. Macromolecules

2003, 36, 27.

Figure 3. Expanded 48-40 ppmregion of 13C NMR spectrum of

Zonyl TM star polymer

C

O

OBr

OO

Rf

4Rf = (CF2)7CF3

n

Synthesis of Well-Defined Highly Branched and GraftCopolymers Having One Branch per Repeating Unit

Based on Living Anionic PolymerizationKenji Sugiyama, Norihide Shimohara, Sang Woo Ryu, and Akira Hirao

Polymeric and Organic Materials Department, Graduate School of Science andTechnology, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku, Tokyo

152-8552, JAPAN

CH2=CH

CH2-O-SiMe2But

sec-BuLi

THF, -78oC20 min CH2-O-SiMe2But

CH2-CH Li

"Living Polymer"

MeOH

CH2-O-SiMe2But

n (CH3)3SiCl

LiBr

n

CH2Br

n

CH2Br

nLiving Anionic Polymer

THF, -40oC1 - 336 h


1-1 Procedure: Synthesis of well-defined poly(3-bromomethylstyrene)1, 2

As illustrated above, poly(m-bromomethylstyrene)s with precisely controlled molecularweights and narrow molecular weight distributions were synthesized by the livinganionic polymerization of 3-(tert-butyldimethylsilyloxymethyl)styrene, followed bytransformation of the tert-butyldimethylsilyloxymethylphenyl group into benzyl bromidefunctionality. All polymerizations and coupling reactions were carried out under highvacuum conditions (10-6 torr) in sealed glass reactors equipped with breakseals.Experimental details on reagent purification and operations using high vacuum linetechnique have been well reviewed by Hadjichristidis and his coworkers.3 A THFsolution (16.5 mL) of 3-(tert-butyldimethylsilyloxymethyl)styrene4 (2.13 g, 8.60 mmol)chilled to -78°C was added at once to sec-butyllithium (sec-BuLi) (0.108 mmol inheptane, 2.25 mL) at -78°C with stirring and the reaction mixture was stirred at -78°Cfor an additional 20 min. After terminating with degassed methanol (3 mL), themixture was poured into a large amount of methanol (300 mL) to precipitate thepolymer. It was reprecipitated twice from its THF solution into methanol and freeze-dried from its absolute benzene solution (3 wt-%) for 24 h. The yield of polymer was2.09 g (98%).

Poly(3-bromomethylstyrene) was prepared by treatment of the poly[3-(tert-butyldimethylsilyloxymethyl)styrene] thus obtained with a 3-fold excess of (CH3)3SiCland LiBr. Poly[3-(tert-butyldimethylsilyloxymethyl)styrene] (1.53 g, 6.17 mmol per tert-butyldimethylsilyloxymethyl groups) dissolved in dry CHCl3 (40 mL) was added to thesuspension of (CH3)3SiCl (1.98 g, 18.3 mmol) and LiBr (1.92 g, 18.3 mmol) in a mixedsolvent of CH3CN (60 mL) and CHCl3 (40 mL) at 25°C and the mixture was allowed tostir at 40°C for an additional 48 h under nitrogen. The mixture was then poured intowater (150 mL) and extracted with CHCl3 (40 mL) three times. The organic layer wasdried over MgSO4, concentrated to ca. 1 mL, and poured into hexanes (200 mL) toprecipitate the polymer. The polymer was reprecipitated twice from its THF solutioninto methanol and freeze-dried three times from its benzene solution (1.11 g, 93%).

1-2 Characterization: Poly[3-(tert-butyldimethylsilyloxymethyl)-styrene] and poly(3-bromomethylstyrene)

Both 1H and 13C NMR spectra were recorded on a Bruker DPX (300 MHz for 1H and 75MHz for 13C) in CDCl3. Size exclusion chromatography (SEC) was obtained at 40°Cusing THF as a carrier solvent with Tosoh HLC 8020 instrument with UV (254 nm) orrefractive index detection. Fractionation by SEC in THF was performed at 40°C usingTosoh HLC 8020 type fully automatic instrument equipped with a TSK-G4000HHR

column (300 mm in length and 21.5 mm in diameter). Vapor pressure osmometry(VPO) measurements for determining absolute Mn values were made in benzenesolution with a sensitive thermoelectric couple and equipment of very exacttemperature control. Static light scattering (SLS) was performed with OtsukaElectronics SLS-600R instrument equipped with a He-Ne laser (λ=632.8 nm) in THF

Synthesis of Well-Defined Highly Branched and Graft Copolymers . . .

or benzene. FT-IR spectra were recorded on a JEOL JIR-AQS20M FT-IRspectrophotometer. Poly[3-(tert-butyldimethylsilyloxymethyl)styrene]: Mn(calcd) = 19.9 kg/mol, Mn(SEC) = 21.9kg/mol, Mw/Mn = 1.02 (SEC); 1H NMR (CDCl3) δ 7.2 – 6.4 (m, 4H, C6H4), 4.60 (s, 2H,CH2OSi), 2.1 – 1.1 (m, 3H, CH2CH), 0.99 (s, 9H, Si-C-CH3), 0.10 (s, 6H, Si-CH3); FT-IR spectrum (KBr): 1253, 838, and 776 cm-1 (SiCH3) and 1081 cm-1 (Si-O).

Poly(3-bromomethylstyrene): Mn(calcd) = 17.2 kg/mol, Mn(SEC) = 14.7 kg/mol, Mn(NMR) =17.5 kg/mol, Mn(VPO) = 17.4 kg/mol, Mw/Mn = 1.02 (SEC); 1H NMR (CDCl3) δ 7.2 – 6.4(m, 4H, C6H4), 4.30 (s, 2H, CH2OSi), 2.1 – 1.1 (m, 3H, CH2CH); FT-IR spectrum (KBr):1210 cm-1 (CH2Br).

SEC of the poly(3-bromomethylstyrene) shows a sharp symmetrical monomodal peak.The observed Mn values by 1H NMR and VPO agreed with that calculated. The 300MHz 1H NMR spectrum shows aromatic protons at 6.4 - 7.2 ppm, a benzyl proton at4.30 ppm, and aliphatic methylene and methin protons at 1.1 - 2.1 ppm. Theresonance at 4.60 ppm assigned to the benzyl proton of benzyl silyl ether completelyshifted toward 4.30 ppm characteristic to the methylene protons of CH2Br group.Moreover, signals corresponding to tert-butyldimethylsilyl methyl protons completelydisappeared. These results clearly indicate that the transformation proceeded cleanlyand quantitatively to afford poly(m-bromomethylstyrene) with a well-controlled chainlength and a narrow molecular weight distribution.

2-1 Procedure: Synthesis of highly branched polystyrenes andgraft copolymers having one branch (graft) chain in each monomerunit1,2

The title highly branched polymers having one chain in each monomer unit weresynthesized by coupling poly(3-bromomethylstyrene) with living anionic polymers ofstyrene, isoprene, 2-vinylpyridine, and tert-butyl methacrylate in THF at -40°C for 1 –336 h. The coupling reactions of poly(3-bromomethylstyrene) with polystyryllithiumand polyisoprenyllithium end-capped with DPE were unexpectedly fast and completewithin 1 h, while 24 h was required in the coupling reaction of living anionic polymer of2-vinylpyridine with poly(3-bromomethylstyrene) under the same conditions. With useof living anionic polymer of tert-butyl methacrylate, more than one week (168 – 336 h)were needed to complete the coupling reaction. Under such conditions, the couplingreactions proceeded cleanly and quantitatively to afford highly branched polystyrenesand graft copolymers having one branch or graft chain in each repeating unit.Furthermore, both branch (or graft) and main chains are precisely controlled. Onlytwo more synthetic examples of such well-defined branched polymers with highlybranched architectures by similar coupling reactions, so-called “grafting-onto” method,have been so far reported by Deffieux et al and Hadjichristidis et al.5,6

Living anionic polymers were prepared as follows: Styrene and 2-vinylpyridine werepolymerized in THF at -78°C for 30 min with sec-BuLi and 1,1-diphenyl-3-


methylpentyllithium prepared from sec-BuLi and a 1.2-fold excess of 1,1-diphenylethylene (DPE). Isoprene was polymerized with sec-BuLi in heptane at 40°Cfor 2 h. The resulting polyisoprenyllithium solution was cooled to -78°C and an equalamount of THF was added. Both polystyryllithium and polyisoprenyllithium were thenend-capped with a 1.5-fold excess of DPE at -78°C for 30 min and 24 h, respectively.Tert-butyl methacrylate was polymerized with diphenylmethylpotassium in THF at-78°C for 1 h. Monomer and initiator solutions were usually in the ranges of 0.5 – 1.0M except for isoprene (3.0 – 4.0 M) and 0.02 – 0.05 M, respectively. Monomersolution was always added to the initiator solution with stirring or shaking.

A typical synthetic procedure of branched polystyrene by the coupling reaction ofpoly(3-bromomethylstyrene) with DPE end-capped polystyryllithium is as follows:Styrene (2.28 g, 21.9 mmol) in THF (24.8 mL) was polymerized with sec-BuLi (0.0331mmol) in heptane (1.01 mL) at -78°C for 20 min and DPE (0.0497 mmol) in THF (1.25mL) was added to the polymerization mixture for 30 min for end-capping. Poly(3-bromomethystyrene) (Mw = 6.75 kg/mol, Mw/Mn = 1.04) (0.00329 g, 0.0165 mmol perbenzyl bromide moiety) dissolved in THF (3.14 mL) was added to the livingpolystyrene solution at -78°C. The reaction mixture was then allowed to stand at-40°C for 1 h. After quenching with degassed methanol (3 mL), the polymer wasprecipitated by pouring the reaction mixture into a large excess of methanol (300 mL).The resulting coupled polymer was isolated nearly quantitatively by fractionalprecipitation described below and purified by reprecipitation from THF into methanoltwice and freeze-dried from its benzene solution for 24 h to yield 1.13 g (99% yield).

The synthesis of poly[styrene-graft-(tert-butyl methacrylate)] was as follows: Tert-butylmethacrylate (1.99 g, 14.2 mmol) in THF (16.8 mL) was polymerized withdiphenylmethylpotassium (0.0601 mmol) in THF (2.03 mL) at -78°C for 4 h. Poly(3-bromomethylstyrene) (Mw = 17.9 kg/mol, Mw/Mn = 1.02) (0.00660 g, 0.0335 mmol ofbenzyl bromide moiety) dissolved in THF (5.34 mL) was added to the living polymersolution at -78°C. The reaction mixture was then allowed to stand at -40°C for 336 h.After quenching with degassed methanol (3 mL), the polymer was precipitated bypouring the reaction mixture into a large excess of methanol (300 mL). Since thehomopolymer of tert-butyl methacrylate is soluble in methanol, the odesired graftcopolymer was isolated nearly quantitatively and purified by reprecipitation from THFinto methanol twice and freeze-dried from its benzene solution for 24 h to yield 1.05 g(96% yield).


Isolation of the branched polymers by fractional precipitation is as follows:

Highly branched polystyrene: The polymer mixture was dissolved in cyclohexane (0.3wt-%). Hexane (16.7 vol-%) was added gradually to the solution and allowed to standat 5°C for overnight. The graft polymer was nearly completely precipitated under theconditions and collected by filtration. It was reprecipitated twice from its THF solutioninto methanol and freeze-dried.

Poly(styrene-graft-isoprene): The graft copolymer was isolated in 70% yield by HPLCfractionation to remove polyisoprene used in excess. The isolated polymer wasreprecipitated from its benzene solution into methanol twice and freeze-dried from itsabsolute benzene solution.

Poly[styrene-graft-(2-vinylpyridine)]: The polymer mixture was dissolved inTHF/methanol (1/1, v/v) (1.0 wt-%). Heptane (71.4 vol-%) was added gradually to thesolution and allowed to stand at 25°C overnight. The branched polymer was nearlycompletely precipitated under the conditions and collected by filtration. It wasreprecipitated twice from its THF solution into heptane and freeze-dried from anabsolute benzene solution containing a small amount of THF.

Poly[styrene-graft-(tert-butyl methacrylate)]: The branched polymer was insoluble inmethanol, while the homopolymer of tert-butyl methacrylate was readily soluble inmethanol. The graft copolymer was therefore isolated by precipitation into methanol.It was reprecipitated twice from its THF solution into methanol and freeze-dried fromits absolute benzene solution.

2-2 Characterization of Graft (co)polymers

The resulting branched polymers were characterized by SEC, SLS, and 1H NMR. Inall samples synthesized and listed in the table shown below, their SEC curves shownarrow symmetrical monomodal peak without any shoulders or tailings. Themolecular weight distributions were very narrow, Mw/Mn values being less than 1.03.Molecular weights estimated by SEC were not reliable because of the reducedhydrodynamic volume caused by their branching architectures. The absolute weightaverage molecular weights were carefully determined by static light scattering (SLS).All of the Mw values agreed quite well within experimental errors with calculated valuesbased on the assumption that all benzyl bromide sites reacted quantitatively with livinganionic polymers. These results strongly indicate quantitative coupling efficiency.

The expected structures and compositions were confirmed by 300 MHz 1H NMRspectra.


main chain

poly(3-bromomethyl-

styrene)

Mw (kg/mol)

graft chain

living polymer

type Mw (kg/mol)

graft (co) polymer,

Mw (kg/mol)

calcd. SEC SLS

Mw/Mn

6.75

17.9

6.75

6.75

6.75

17.9

17.9e)

PSb) 5.90

PS 7.80

PS 24.7

PS 68.8

PIc) 24.5

P(2VP)d) 16.3

P(tBMA)f) 31.6

165 64 161

704 178 717

810 272 860

2274 578 2310

812 315 847

1461 502 1490

2823 481 2830

1.02

1.02

1.02

1.03

1.02

1.02

1.02

Table. Molecular Weight and Polydispersity Data5

a) Reactions were carried out in THF at -40°C for 24 h. Yields were quantitative in all cases. b)

Polystyryllithium end-capped with 1,1-diphenylethylene (DPE). c) Polyisoprenyllithium end-capped withDPE. d) Poly(2-vinylpyridinyl)lithium. e) The reaction was carried out for 336 h. f) Diphenylmethylpotassiumwas used as an initiator.

3.References

1. Ryu, S.-W.; Hirao A. Macromolecules 2000, 33, 4765.2. Ryu, S.-W.; Hirao A. Macromol. Chem. Phys. 2001, 202, 1727.3. Hadjichristidis, N.; Iatrou, H.; Pispas, S.; Pistikalis, M. J. Polym. Sci. Part A.

Polym. Chem. 2000, 32, 3211.4. Hirao, A.; Kitamura, K.; Takenaka, K.; Nakahama, S. Macromolecules 1993, 26,

4995.5. Schappacher, M; Deffieux, A. Macromol. Chem. Phys. 1997, 198, 3953. 6. Schappacher, M.; Billaud, P.; Paulo, C. ; Deffieux, A. Macromol. Chem. Phys.

1999, 200, 2377.7. Tsukatos, T.; Pispas, S.; Hadjichristidis, N. Macromolecules 2000, 33, 9504.


Figure 1. 1H NMR spectra of poly[3-(tert-butyldimethylsilyloxymethyl)styrene] (A), poly(3-bromomethylstyrene) (B), and their expanded regions (A', B')

Figure 2. SEC curves of poly(3-bromomethylstyrene) before (dashed line) and after

(solid line) the transformation reaction


Figure 3. SEC curves of branched polystyrenebefore (dashed line) and after (solid line)

fractionation.

Synthesis and Deposition of (11-(2-Bromo-2-methyl)propionyloxy)undecyltrichlorosilane

Stephen G. Boyes1, Anthony M. Granville2 and William J. Brittain2

CH2

(CH2)9

OH

Br

O

CH3 Br

CH3+CH2

(CH2)9

O

Br

O

CH3

CH3

Pyridine

THF

HSiCl3

'Pt'

ClSi

(CH2)11

O

Br

O

CH3

CH3

ClCl

Si OH

Si OH

Cl3Si (CH2)11 O C

O

C

CH3

CH3

Br

(CH 2)11 O C

O

C

CH3

CH3

BrO Si

O

OToluene, 60 oC, 4 h

1.Procedure

a. 10-Unden-1-yl 2-Bromo-2-methylpropionate3

2-Bromoisobutyryl bromide (6.8 mL, 55 mmol) was added drop-wise to a stirredsolution of ω-undecylenyl alcohol (10 mL, 53 mmol) and pyridine (4.8 mL, 59 mmol) indry tetrahydrofuran (THF) (50 mL). The mixture was stirred at room temperatureovernight (Note 1) followed by dilution with hexane (100 mL). The mixture was thenwashed once with 2 N HCl and twice with water. The organic phase was dried overanhydrous sodium sulfate for 6 h and filtered. The solvent was removed from thefiltrate under reduced pressure and the residue was purified by flash columnchromatography using silica gel as the stationary phase and hexane/ethyl acetate(25/1 v/v) as the eluent. The solvent was then removed in vacuo to give a yield of12.87 g (77%) of 10-undecen-1-yl 2-bromo-2-methylpropionate as a colorless oil. 1HNMR (300 MHz, CDCl3): δ: 1.23-1.37 (br m, 12H); 1.63-1.70 (m, 2H); 1.93 (s, 6H);2.03-2.07 (q, 2H); 4.14-4.18 (t, 2H); 4.91-5.02 (m, 2H); 5.78-5.86 (complex m, 1H)ppm.


b. (11-(2-Bromo-2-methyl))propionyloxy)undecyltrichlorosilane3

To a solution of 10-undecen-1-yl 2-bromo-2-methylpropionate (11.54 g, 36 mmol) intrichlorosilane (25 mL, 250 mmol) was added a 1:1 (v/v) ethanol/diethyl ether solutionof chloroplatinic acid, H2PtCl6 (110 mg, 5 mL). The mixture was gently refluxed at40°C for 4 h. Excess trichlorosilane was removed under reduced pressure followedby dilution with CH2Cl2 (Note 2). The solution was then filtered through a short columnof anhydrous magnesium sulfate followed by removal of solvent under reducedpressure. The product, 13.73 g (84%), was then used without further purification. 1HNMR (300 MHz, CDCl3) δ: 1.28-1.44 (br m, 16H); 1.56-1.73 (m, 4H); 1.93 (s, 6H);4.15-4.19 (t, 2H) ppm.

c. Deposition of (11-(2-Bromo-2-methyl))propionyloxy)undecyltrichlorosilane

Into a dried 20 mL round-bottom flask was placed a freshly cleaned silicon wafer andATR crystal and the flask was sealed with a septum. Dry toluene (10 mL) and a25wt-% solution of initiator in toluene (0.15 mL (Note 3)) were added to the flask viasyringe and the flask was heated at 60°C for 4 h. The silicon wafer and ATR crystalwere then removed and sequentially washed with toluene, CH2Cl2 and ethanol; andthen dried in a stream of air. The ATR-FTIR spectrum of deposited (11-(2-bromo-2-methyl))propionyloxy)undecyltrichlorosilane is given in Figure 3. The peaks at 2853and 2925 cm-1 were assigned to the CH2 stretching and C-H stretching vibration,respectively. The peak at 1736 cm-1 was assigned to the carbonyl stretching vibrationof the ester group. The contact angles, determined using high purity HPLC water,were θadvancing = 87° and θreceding = 74° (Note 4). The thickness of deposited (11-(2-bromo-2-methyl))propionyloxy)undecyltrichlorosilane was determined by ellipsometryand was typically 1.9 ± 0.3 nm (Note 5). [See Note 6 and Figure 4 for potential sidereaction observation].

2.Characterization

ATR-FTIR spectra were recorded using a Nicolet System 730 spectrometer using amodified 4XF beam condenser (Harrick Scientific). Spectra were recorded at 2 cm-1

resolution and 500 scans were collected. Contact angles were determined using aRamé-Hart NRL-100 contact angle goniometer equipped with an environmentalchamber and tilting base mounted on a vibrationless table (Newport Corp.).Advancing and receding values were determined using the tilting stage method at anangle of 35°. Drop volumes were 10 µL. Ellipsometric measurements wereperformed on a Gaertner model L116C ellipsometer with He-Ne Laser (λ = 632.8 nm)and a fixed angle of incidence of 70°. For calculation of the layer thickness, refractiveindices of n = 1.455 (for silicon oxide)4 and n = 1.508 (for the initiator layer) were used.1H NMR spectra (δ, ppm) were recorded on a Bruker AM-300 (300 MHz) spectrometerin CDCl3.

Synthesis and Deposition of (11-(2-Bromo-2. . .

3.Notes

1. The reaction flask was covered with aluminum foil to reduce the exposureto light.

2. A bulb-to-bulb distillation technique, with a slightly reduced pressure, wasused due to the low boiling point of trichlorosilane (~37°C). CAUTION – Thelarge excess of trichlorosilane may cause the solution to “bump” over intothe collection flask. Be sure to include a stir bar in the solution to aid in theboiling of the trichlorosilane. Also, leaving the catalyst (which has atendency to precipitate out), acts to aid in trichlorosilane removal.

3. Rather than storing raw trichlorosilane initiator, the initiator was diluted withdistilled toluene to afford a 25% w/w solution. The solution was wrapped inaluminum foil to reduce light exposure, and stored in a chemical freezer.

4. Variation in contact angles is typically ± 2° for θadvancing and ± 3° for θreceeding

with hysteresis (the difference between the two measurements) of 12° ± 2°.5. Theoretical thickness for initiator layer, assuming no vertical or horizontal

crosslinking and a 10° tilt angle, was calculated to be 2.02 nm based onstandard bond angles and lengths.

6. Occasionally, during the deposition of the initiator, a peak at 2250 cm-1 thatvaries in relative intensity appears (Figure 2). This has been attributed tothe appearance of Si-H species. The appearance of this species tends tolower the overall initiator layer thickness and affects the initiating capabilityof the deposited initiator. Removing the excess trichlorosilane first andusing repeated reduced-pressure distillations during the initiator synthesiscan remove the Si-H peak entirely.

4. References

1. School of Polymers and High Performance Materials, The University ofSouthern Mississippi, Hattiesburg MS 39406-0076.

2. Department of Polymer Science, The University of Akron, Akron OH 44325-3909.

3. Matyjaszewski, K.; Miller, P. J.; Shukla, N.; Immaraporn, B.; Gelman, A.;Luokala, B.B.; Siclovan, T. M.; Kickelbick, G.; Vallant, T.; Hoffmann, H.;Pakula, T. Macromolecules 1999, 32, 8716.

4. Brandrup, J.; Immergut, E. H.; Grulke, E. A. Polymer Handbook 1999, Eds.;Wiley & Sons: New York.


Figure 2: 1H NMR spectrum of (11-(2-bromo-2-methyl))propionyloxy)undecyltrichlorosilane

Figure 1. 1H NMR spectrum of 10-unden-1-yl 2-bromo-2-methylpropionate

Synthesis and Deposition of (11-(2-Bromo-2. . .

Figure 3: ATR-FTIR Spectrum of deposited (11-(2-bromo-2-methyl))propionyloxy)undecyltrichlorosilane

Figure 4: ATR-FTIR Spectrum of deposited (11-(2-Bromo-2-methyl))propionyloxy)undecyltrichlorosilane containing Si-H impurity

Synthesis of Block Copolymers viaMacroiniter/Macroiniferter

Metin H. Acar1, Perihan Demircioglu1, Meltem Kucukoner1, Ayhan Gulkanat1,Sedat Seyren1, Gurkan Hizal1, Yusuf Yagci.1

Scheme 1


Scheme 2

Scheme 3

Synthesis of Block Copolymers

Scheme 4

Scheme 5


1.Procedure, triphenylmethyl (Trityl) terminated polymethacrylonitrile,Tr-PMAN (Scheme 1).

Methacrylonitrile (MAN) and phenylazotriphenylmethane (PAT) (MAN: 10 mL, 12mol/L, PAT: 0.01 g, 3x10-3 mol/L for bulk polymerization; MAN: 10 mL, 6 mol/L, PAT:0.07 g, 1x10-2 mol/L, cyclohexanone: 10 mL for solution polymerization) were placedto the polymerization tube containing a magnet. The polymerization tube wasdegassed 3 times by freeze-pump-thaw technique and sealed, then placed in aconstant temperature oil bath at 65oC for bulk and 80oC for solution polymerization.After given time, polymer was obtained by precipitation (Note 1). Conversion wasincreased by time and linear relationship was observed between conversion andmolecular weight in both bulk and solution polymerizations. Molecular weight of thepolymer was reached to 37300 g/mol, (Mw/Mn: 1.38) after 120 hours.

2.Characterization, trityl terminated polymethacrylonitrile, Tr-PMAN.

The UV spectrum (Note 2) of the polymer possesses an absorption band at aroundthe 330 nm region, indicating attachment of trityl end group in PMAN.

The number average molecular weights (Mn) were measured from GPCchromatograms (Note 3).

Scheme 6


3.Procedure, block copolymers using macroiniter Tr-PMAN(Scheme 1).

Tr-PMAN (1 g, 22.7 g/L, Mn: 37300 g/mol, Mw/Mn: 1.38), 2,3,3,4,4,4-hexafluorobutylmethacrylate (HFBMA: 4 mL, 0.49 mol/L) and cyclohexanone (40 mL) were placed toa polymerization tube containing a magnet. The polymerization tube was degassed 3times by freeze-pump-thaw technique and sealed. The tube was placed in a constanttemperature oil bath at 80 oC. The homoPHFBMA was removed from the blockcopolymer by extracting with methanol.

4.Characterization, block copolymers using macroiniter Tr-PMAN.


Conversion was increased by time and linear relationship was observed betweenconversion and molecular weight. Results are shown in Table 1.

Table 1: Conversion and molecular weight for block copolymerization of HFBMA byinitiated Tr-PMAN as macroinitera.

Time, h Conversion, % ∆Mnb Μw/Μn

2.5 13.3 2380 1.435.0 21.4 3470 1.38

21.0 51.3 7640 1.4245.0 60.9 9300 1.39

a) Tr-PMAN: 1 g, 22.7 g/L, Mn: 37300 g/mol, HFBMA: 4 mL, 0.49 mol/L,cyclohexanone: 40 mL, 80°C.

b) Measured in GPC based on polymethyl methacrylate standard. Eluent: ethylmethyl ketone, 1 mL/min, ∆Mn= Mn(Block copolymer) – Mn(PMAN).

5.Procedure, trityl terminated polystyrene and polymethylmethacrylate, Tr-PS, Tr-PMMA (Scheme 2).

Styrene (S, 20 ml, 8.73 mol/L) or methyl methacrylate (MMA, 20 mL, 9.36 mol/L), 2,2’-azobisisobutyronitrile (AIBN, recrystallized from methanol, 0.0082 g, 2.5x10-3 mol/L)and triphenylmethyl mercaptan (TPMM, 0.0055 - 0.0275 g, 1x10-3 - 5x10-3 mol/L) asmonomer, initiator and chain transfer agent, respectively, were placed in a Schlenktube. The Schlenk tube was degassed 3 times by freeze-pump-thaw technique, andthen put into constant temperature oil bath at 70°C. At the end of the reaction after~15 minutes, polymer was isolated by precipitation (Note 4). The conversion of themonomer was kept under 7% for each of the polymerizations.


6.Characterization, trityl terminated polymers, Tr-PS, Tr-PMMA.

IR spectum (Note 5) shows triphenylmethyl (trityl) moieties in the obtained polymers,Tr-PS and Tr-PMMA. The stretching band at 2570 cm-1, due to -SH group in theTPMM, disappeared in the polymers.

The 1H-NMR spectrum (Note 6) showed peaks at 7.2 ppm, 3.6 ppm and 1.4-2.0 ppmcorresponding to aromatic, –OCH3 and aliphatic protons, respectively, thus indicatingthe presence of trityl end group in PMMA.

The UV spectrum (Note 2) of the polymer possesses an absorption band at around330 nm, indicating again the presence of the trityl end group in PMMA.


Transfer constants of TPMM were found to be 17.8 and 0.71 for styrene and MMA,respectively (Note 8).

7.Procedure, block copolymers using macroiniter Tr-PS or Tr-PMMA (Scheme 2)

Trityl terminated polystyrene (Tr-PS, 80 g/L, Mn=49800 g/mol) with MMA (10 mL, 9.36mol/L) or trityl terminated PMMA (Tr-PMMA, 40 g/L, Mn=110600 g/mol) with styrene(10 mL, 8.73 mol/L) were placed in a Schlenk tupe containing a magnet. The Schlenktube was degassed 3 times by freeze-pump-thaw technique. After 3 hours for MMApolymerization and 2 hours for styrene polymerization, polymer was isolated byprecipitation (Note 4). Block copolymers were freed from homopolystyrene andhomopoly(methyl methacrylate) by extracting them from boiling cyclohexane andacetonitrile, respectively. After extraction, block copolymers PS-b-PMMA (Mn=110700g/mol, 52% block efficiency) or PMMA-b-PS (Mn=142500 g/mol, 66% block efficiency,19.4% PS content in block copolymer) were obtained.

8.Characterization, block copolymers using macroiniter Tr-PS orTr-PMMA


Block copolymer composition was calculated by the comparison of the peaks area at3.6 ppm for -OCH3 and 7.2 ppm for aromatic protons in the 1H-NMR spectrum (Note6) of PMMA-b-PS.


9.Procedure, trityl terminated polymers, Tr-PBVE (Scheme 3). Butyl vinyl ether (BVE, 32.3 mL, 2 mol/L) and tetrahydrothiophene (THT, 2.2 mL, 2mol/L) as momomer and carbocation stabilizer, respectively, in dichloromethane(CH2Cl2, 20 mL) were put into a polymerization tube sealed by rubber septum. Thepolymerization tube was outgassed 3 times by freeze-pump-thaw technique andplaced into an ethyl alcohol bath kept at –30°C. Then, triphenylcarbonium tetrafluoroborate (Tr + BF4

¯, 0.763 g, 2x10-2 mol/L) as a cationic initiator in 20 mL of CH2Cl2was added to the polymerization tube by syringe. After 1 hour, the mixture was pouredinto 1L of methanol containing ditertierbutylpyridine (DTBP, 0.65 ml) as a base. Tr-PBVE was obtained after decantation of solvents drying of residual in vacuum oven.

10.Characterization, trityl terminated polymers, Tr-PBVE.

The 1H-NMR spectrum (Note 6) showed the aromatic protons peaks at 7.2 ppm, inaddition to the peaks at 3.5 ppm for –O–CH– and –O–CH2–, and 0.9-1.9 ppm forCH2–CH–O– and alkyl protons, respectively, supporting the presence of trityl endgroup in PBVE. Molecular weight was calculated by the comparison of the peaks areaat 3.5 ppm for –O–CH– and –O–CH2–and 7.2 ppm for aromatic protons in the 1H-NMRspectrum of Tr-PBVE.

The UV spectrum (Note 2) of the polymer possesses an absorption band at around262 nm region, indicating again the presence of the trityl end group in PBVE.Molecular weight of Tr-PBVE was calculated from the UV absorbance value, using ε=1305 L. mol-1. cm-1 as a molar extinction coefficient in the equation (A= ε.l.c) based ontrityl group (Note 9).

The number average molecular weights (Mn) were measured by GPC analysis (Note 10).

The results are shown in Table 2.

Table 2: The polymerization of butyl vinyl ether using Tr + BF4¯ and THTa.

Time Conv. Molecular Weight h % Mn(calc)

b Mn(U.V.)c Mn(NMR)

d Mn(GPC)e Mw/Mn

e

0.5 77.2 7720 8330 8860 7000 1.181.0 93.2 9320 9280 10300 10100 1.21

a) [BVE]=2 mol/L, [Tr + BF4¯]=2x10-2 mol/L, [THT]=2 mol/L, –30°C.

b) Mn(calc)=([BVE] / [Tr + BF4¯]). Conversion %. MBVE.


c) ε= 1305 L. mol-1. cm-1. d) Calculated from 1H-NMR.e) Based on polystyrene standard. Eluent: THF, 1mL/min.

11.Procedure, block copolymers using macroiniter Tr-PBVE(Scheme 4).

Tr-BVE (1 g, 50 g/L, Mn: 10100 g/mol) and MMA (10 mL, 4.68 mol/L) mixtures intoluene (10 mL) were put into a Schlenk tupe containing a magnet. The Schlenk tubewas degassed 3 times by freeze-pump-thaw technique, then put into an oil bath at 80or 90°C. Adequate samples were taken during the polymerization. After a givenpolymerization time, the polymer was isolated by precipitation (Note 4). Blockcopolymers were freed from homopolybutyl vinyl ether by extracting them from carbontetrachloride.

12.Characterization, block copolymers using macroiniter Tr-PBVE.

The number average molecular weights (Mn) were measured by GPC (Note 11).

The linear relationship was observed between conversion and molecular weight.Results are shown in Table 3.

Table 3: The block polymerization of MMA using Tr-BVE as macroinitera.Time, h Conv., % Mn

b ∆Mnb Mw/Mn

b Block copolymer,

%c

0d 0.0 10100 - 1.21 0.07 0.7 12800 2700 1.34 20.7

14 18.9 27800 17700 1.29 81.321 20.3 32100 22000 1.32 84.430 38.1 46400 36300 1.27 91.041 84.4 77200 67100 1.30 97.6

a) [Tr-PBVE]: 50 g/L (Mn: 10100 g/mol), [MMA]: 4.68 mol/L, toluene: 10 mL, 80°C. b) Measured in GPC based on polystyrene standard. Eluent : THF, 1 mL/min,∆Mn

: Mn(block copolymer) - Mn(Tr-PBVE).c) Fraction extracted from CCl4, insoluble part.d) Tr-PBVE precurser.


1.Procedure, N,N'-diethyldithiocarbamate terminated polytetrahydrofuran, C-PTHF (Scheme 5).

A three-necked flask equipped with nitrogen inlet and a rubber septum was connectedto a vacuum line.The flask was dried at 130°C under vacuum. After cooling at roomtemperature, tetrahydrofuran (THF, 50 mL, 12.3 mol/L) as a monomer was freshlydistilled into the flask under the vacuum (Note 11). The flask was then disconnectedunder nitrogen and placed into constant temperature alcohol bath at 25°C.Trifluorosulfonic acid anhydride (TFA, 0.104 mL, 1.23x10-2 mol/L) as bifunctionalinitiator was added to the flask by syringe. After 25 minutes, living PTHF wasterminated by the addition of N,N'-diethyldithiocarbamic acid sodium salt (NaDC,0.123 mol/L) in 10 ml of THF. The mixture was stirred for 15 minutes at 25°C, thenpoured into methanol and cooled to –30°C. The precipitated polymer was, thenfiltered, dried in vacuum. The desired N,N'-diethyldithiocarbamate terminatedpolytetrahydrofuran (C-PTHF) was obtained as a white powder.

14.Characterization, N,N'-diethyldithiocarbamate terminatedpolytetrahydrofuran, C-PTHF.

The UV spectrum (Note 2) of the polymer possesses an absorption band at aroundthe 278 nm region, indicating attachment of N,N'-diethyldithiocarbamate end group toPTHF. Molecular weight of Tr-PTHF was calculated from the UV absorbance value,using ε= 13500 L. mol-1. cm-1 as a molar extinction coefficient in the equation (A= ε.l.c)based on N,N'-diethyldithiocarbamate group2.

The 1H-NMR spectrum of C-PTHF (Note 6) was shown a typical PTHF signal for–O–CH2– protons at 3.4 ppm and –OCH2–CH2–peaks protons at 1.6 ppm.

The number average molecular weights (Mn) were measured by GPC (Note 11).Molecular weights were multiplied by a factor of 0.556 for PTHF3. Molecular weightresults are shown in Table 4.

Table 4: The Characterization of C-PTHFa.Mn(Calc)

b Mn(U.V.)c Mn(GPC)

d Mn(GPC-PTHF)e Mw/Mn

d

10600 10300 16600 9200 1.25

a) [THF]=12.3 mol/L, [TFA¯]=1.23x10-2 mol/L, [THT]=2 mol/L, conversion: 14%,25 minute, 25°C.

b) Mn(calc)=([THF] / [TFA¯]). Conversion %. MTHF.c) ε= 13500 L. mol-1. cm-1.d) Measured in GPC based on polystyrene standard. Eluent:THF, 1mL/min.e) Calculated by Mn(GPC-PTHF)= 0.566 x Mn(GPC) for PTHF.


15.Procedure, block copolymer using macroiniferterter C-PTHF(Scheme 6).

C-PTHF (0.2 g, 50 g/L, Mn(GPC):16600 g/mol) and MMA (2 ml, 4.68 mol/L) were put intopyrex tube (i.d. 10 mm) in dichloromethane (2 mL). The tube was degassed underhigh vacuum and sealed under nitrogen prior to irradiation at ~300 nm in a Rayonetreactor equipped with rotating sample holder. Appropriate cut-off filters were placed infront of the tube. After photolysis for a given time at 25°C (HOW LONG), blockcopolymer was isolated by precipitation into methanol. Since the precursor C-PTHFdissolves in methanol at room temperature and precipitates at low temperature, i.e.<20°C, this temperature dependent solubility or insolubility was used to remove theunreacted C-PTHF from the block copolymer.

16.Characterization, block copolymer using macroiniferter C-PTHF.

The 1H-NMR spectrum (Note 6) of block copolymer was taken in CDCl3 at ambienttemperature. The molecular weight of the block copolymer (Mn(NMR)) wascalculated.using the ratio of the peaks area of –OCH3 protons at 3.6 ppm coming fromthe PMMA to –O–CH2– protons of the PTHF at 3.4 ppm.

The IR spectra (Note 12) of the block copolymers showed the characteristic carbonylband at 1730 cm-1 and the ether band 1100 cm-1 indicating the presence of both THFand MMA segments.

The number average molecular weights (Mn) were measured by GPC (Note 10).

The result is shown in table 5.

Table 5: The photopolymerization of MMA using C-PTHF as macroinifertera.

Time, h Conversion, % Mn(NMR)b ∆Mn

c Mw/Mnc

1 1.2 - 63600 1.522 8.8 93400 80800 1.454 11.1 - 85900 1.498 37.1 - 97100 1.6416 87.1 165000 140900 1.32

a) [C-PTHF]: 0.2 g (Mn: 16600 g/mol), [MMA]: 2 mL, 4.68 mol/L, 2 mL CH2Cl2,25°C, λ=~300 nm. Data values represent for room temperature fractions.

b) Calculated from 1H-NMR.c) Measured in GPC based on polystyrene standard. Eluent : THF, 1 mL/min,∆Mn

: Mn(block copolymer) - Mn(C-PTHF).


17.Methods of preparation

The macroiniter/macroiniferter (initiator-transfer agent-terminator) is one of thesuitable methods to synthesize block copolymer4. Several organic disulfides andphenylazotriphenylmethane were found to serve as photo or thermal iniferters2,4,5. Themacroiniter trityl terminated poly(methacrylonitrile) can be synthesized by living radicalpolymerization using phenylazotriphenyl methane as a thermal iniferter6. Tritylterminated polystyrene or poly(methyl methacrylate) can be synthesized by radicalpolymerization of styrene or methyl methacrylate using triphenylmethyl mercaptane asa chain transfer agent7. Trityl terminated poly(butyl vinyl ether) can be obtained bycationic polymerization of butyl vinyl ether using triphenylcarbonium tetrafluoro borateas a cationic initiator8. Then, these macroiniters (trityl terminated polymers) can beused to obtain block copolymers via radical polymerization of a second monomer6-8.The macroiniferter, N,N'-diethyldithiocarbamate terminated polytetrahydrofuran can besynthesized by cationic polymerization of tetrahydrofuran using N,N'-diethyldithiocarbamic acid sodium salt as a chain terminating agent9. After that, N,N'-diethyldithiocarbamate terminated polytetrahydrofuran can be used as a bifunctionalinitiator (macroiniferter) in photo polymerization of methyl methacrylate to yield blockcopolymers9.

Notes

1. Adequate samples were taken during the polymerization and poured into ten-fold excess of n-hexane, filtered and dried to constant weight in the vacuumoven at 50°C. Conversion was calculated by gravimetric analysis. Polymerswere redissolved in acetone and reprecipitated inton-hexane to yield thepolymer as a fine white powder.

2. UV-Vis spectra were recorded on a Perkin-Elmer (model Lambda 2)spectrophotometer in CH2Cl2 solution.

3. Number average molecular weigths of the polymers were measured by GPCchromatography with set-up consisting of a Pump, Differential Refractometer(model Knauer M-64) and Ultrastyragel columns with porosities mix, 500 and 10Ǻ, respectively. Ethyl methyl ketone was used as eluent at a flow rate of 1mL/min. Samples were injected to 50 µL sample loop. Concentrations werenormally in the range of 2-3%w/v. Molecular weights were calculated with theaid of polymethylmethacrylate standard.

4. At the end of the reaction, mixtures were poured into ten-fold excess methanol,and the precipitated polymer was then filtered and dried to constant weight in avacuum oven at 50°C. Conversion was calculated by gravimetric analysis. TheIsolated polymer was redissolved in dichloromethane and was reprecipitatedinto methanol to yield the final polymer as a fine white powder.

5. IR spectra were recorded on a Shimadzu IR-400 spectrophotometer.6. 1H-NMR spectra were obtained using a Bruker 200 MHz spectrometer in CDCl3

solution with tetramethyl silane as internal standard.


7. Number average molecular weigths of the polymers were measured by GPCchromatography with set-up consisting of a Pump, Differential Refractometer(model Knauer M-64) and Ultrastyragel columns with porosities mix, 500 and 10Ǻ, respectively. THF was used as eluent at a flow rate of 1 ml/min. Sampleswere injected to 50 µL sample loop. Concentrations were normally in the rangeof 2-3%w/v. Molecular weights were calculated with the aid of polystyrenestandard.

8. Obtained from plots of reciprocal degree of polymerization (1/Pn) versus [S]/[M],S: TPMM, M: S or MMA.

9. Value was calculated in our own laboratory based on the callibration curveobtained from the UV absorbance at the different concentrations of Tr + BF4

¯.10.Number average molecular weigths of the polymers were measured by GPC

chromatography with set-up consisting of a Water pump (model 600E),Ultrastyragel columns with porosities 500 and 10, respectively. THF was usedas eluent at a flow rate of 1 ml/min and detections were carried out with WatersDifferential Refractometer (model 410). Samples were injected to 20µL sampleloop. Concentrations were normally in the range of 2-3 w/v. Molecular weightswere calculated with the aid of polystyrene standard.

11.THF was dried over potassium hydroxide, distilled over sodium wire and finallydistilled over sodium/benzophenone kethyl prior to use.

12.IR spectra were recorded on a JASCO 500 spectrophotometer.

References

1. Istanbul Technical University, Chemistry Department, Maslak, 34469 Istanbul,Turkey. E-mail: [email protected] (Metin H. Acar).

2. T. Otsu, M. Yoshida, Macromol. Chem. Rapid. Commun., 3, 127 (1982).3. F. J. Burges, A. V. Cunliffe, D. H. Richards, D. Thompson, Polymer, 19, 334

(1978).4. T. Otsu , T. Matsunaga, A. Kuriyama, M. Yoshioka, Eur. Polym. J., 25, 643

(1989).5. T. Otsu, T. Tazaki, Polymer Bull., 16, 277 (1986).6. M. H. Acar, Y. Yagci, J. Macromol. Sci. Macromol. Reports, A28 (Suppl. 2), 177

(1991).7. P. Demircioglu, M. H. Acar, Y. Yagci, J. Appl. Polym. Sci., 46, 1639 (1992).8. M. H. Acar, M. Kucukoner, Polymer, 38, 2829 (1997).9. M. H. Acar, A. Gulkanat, S. Seyren, Polymer, 41, 6709 (2000), Erratum: 42,

1767 (2001).

s-Bu

(I)

Li

SiCl

s-BuLi

(I)

(II)

s-Bu

s-Bu Si

Lin

_ +

n_ +

(fast)

(slow)

n

n

_ +

+ LiCl

Cl

Mg

Mg Cl

ClSi

Cl

TH F

Si

Cl

+ Mg Cl2

Structurally Modified Polystyrenes via Convergent LivingAnionic Polymerization

Submitted by: Tianzi Huang and Daniel M. Knauss1

1.Procedure

a. 4-(Chlorodimethylsilyl)styrene (CDMSS)2, 3

Magnesium shavings (5.2 g, 0.21 mol) were added to a 250 mL, three-necked, round-bottom flask equipped with an addition funnel and condenser. The glass apparatusand the magnesium shavings were flame dried in the presence of two crystals ofiodine under a flow of argon. After cooling, 10 mL of THF (Note 1) was added alongwith several drops of 1,2-dibromoethane, and the THF was warmed to reflux using avariac-controlled heating mantle. Freshly distilled p-chlorostyrene (25 g, 0.18 mol)(Note 2) in 70 mL THF was added dropwise from the addition funnel while maintainingthe reflux of THF. The p-chlorostyrene was added over approximately 0.5 hours andthe reaction continued to stir for 2-3 hours without external heating. The Grignardreagent was separated from the residual magnesium by transferring to an additionfunnel using a double-tipped needle, and added dropwise to an ice-bath-cooledsolution of freshly distilled dichlorodimethylsilane (54 g, 0.42 mol) in 30 mL THF. Thereaction stirred overnight, after which the salts were filtered and the THF and residual


dichorodimethylsilane were removed by rotary evaporation. The product was distilledunder vacuum (0.2 mm Hg) at 60-65°C to yield 24 g of product (70%).

b. Star-shaped and hyperbranched polystyrenes2, 4

Linear Polystyrene. Styrene (2.5 mL, 22 mmol) (Note 3) and 100 mL cyclohexane(Note 4) were transferred by syringe into a dry, rubber septum-sealed, argon-purged,250 mL round-bottom flask with a glass coated magnetic stir bar. sec-Butyllithium (2.5mL, 2.8 mmol) was then added by syringe. After thirty minutes, 3 mL THF was addedto the reaction mixture. An aliquot (5 mL) of the linear oligomer solution was removedand precipitated into argon-purged methanol.

The coupling agent, CDMSS, was redistilled under vacuum just prior to use, then wasadded either diluted with cyclohexane (approximately 0.50 M) or mixed with styrene ina calculated molar ratio, such as 1:10, to prepare star-shaped or hyperbranchedstructures, respectively. The CDMSS solution was added at a slow rate to the linearoligomer solution until the red color of the polystyryllithium disappeared (Note 5). Theresulting polymers were isolated by precipitation in to methanol and were dried undervacuum at 50°C. The reaction yield is quantitative after considering the aliquotremoved during sampling.

c. Star-block-linear-block-star polystyrene5

Initial linear polystyrene living chains were synthesized as described above. A solutionof CDMSS in cyclohexane (approximately 0.50 M) was added at a rate of 1.0 mL/hourto the initial linear polystyrene living chains to introduce a total of 4.5 mL. The amountof stoichiometric deficiency of CDMSS controls the average number of arms of theliving stars (Note 6). Thirty minutes after complete addition, an aliquot (5 mL) wasremoved and precipitated in to argon-purged methanol. To the living polymer solution,styrene (2.0 mL, 17 mmol) was added slowly to minimize any temperature increase ofthe reaction solution. The solution was allowed to react for one more hour and thenthe reaction mixture was again sampled. Dichlorodimethylsilane (1.0 mL) was diluted

Structurally Modified Polystyrenes via Convergent Living Anionic Polymerization

in 10 mL THF (to approximately 0.75 M) and added into the living anion solution at arate of 0.2 mL/hour until the reaction solution turned colorless. The reaction mixturewas then precipitated to methanol, filtered, washed with methanol, and dried to aconstant weight at room temperature in a vacuum oven. The total yield of polymer wasquantitative after accounting for the sampled aliquots. This sample was further purifiedby fractionation (Note 7).

d. Radially linked star-block-linear polystyrene, ((PS)nPS)m6

Polystyrene initial living chains were synthesized as described in Procedure B. Asolution of CDMSS in cyclohexane (approximately 0.50 M) was then added at a rate of1.0 mL/hour. A 3.8 mL mixture of CDMSS, cyclohexane was added over the course ofapproximately 4 hours [Note 6]. One hour after the complete addition, an aliquot (5 mLsolution) was removed and precipitated into argon-purged methanol. Styrene (8.0 mL,70 mmol) was added slowly to avoid any temperature increase of the reactionsolution. One hour after complete addition, an aliquot (5 mL solution) was removedand precipitated into argon-purged methanol. CDMSS in cyclohexane (approximately0.50 M) was added at a rate of 0.4 mL/h until the reaction solution turned colorless. Atotal of about 2.0 mL of CDMSS/cyclohexane mixture was added over the course of 5h. The polymer was isolated by precipitation into methanol followed by filtration,washing with methanol, and drying at room temperature under vacuum. Yield of thefinal product was quantitative after considering the removed aliquots. This sample wasfurther purified by fractionation (Note 8).

2.Characterization

a. 4-(Chlorodimethylsilyl)styrene (CDMSS)

CDMSS is a transparent liquid with a density of 1.04 g/mL at room temperature (Note9) and a boiling point of 60-65°C (~0.2 mmHg).

1H NMR (Note 10): δ 0.73 ppm (s, –Si–(CH3)2); δ 5.34 and 5.37 ppm (d,CH(Ph)=CHa(H)); δ 5.84 and 5.89 ppm (d, CH(Ph)=CH(Hb)); δ 6.73 - 6.81 ppm (tetra,CH(Ph)=CH2); δ 7.49 and 7.50 ppm (d, Ph-Hd), δ 7.64 and 7.66 ppm (d, Ph-Hc). 29SiNMR (Note 11): δ 19.8 ppm (s, Cl–Si(CH3)2-).

SiH3C CH 3

Cl

H a

Hb H

HcHc

Hd Hd


b. Star-shaped and hyperbranched polystyrenes

1H NMR: δ 0.1 ppm (s, –Si–(CH3)2); δ 1.3-2.3 ppm (m, –CH(CH3)CH2CH3 and–CH(Ph)–CH2–); δ 6.4-7.2 ppm (m, Ph-H). 29Si NMR: δ -2.8 ppm (s, -(Ph)CH–Si(CH3)2-Ph).

Molecular weight characterization of star-shaped polystyrene by GPC-MALLS (Note12): the Mn of initial chain is 940 g/mol, the polydispersity index (PDI, Mw/Mn) is 1.04;the Mn of the resulting star is 12,100 g/mol and, PDI is 1.14. The calculated averagenumber of arms is 11 (Note 13), the intrinsic viscosity is 0.06 dL/g (Note 14), and themeasured glass transition temperature is 75°C (Note 15).

Molecular weight characterization of hyperbranched polystyrene (1:10 molar ratio ofCDMSS to styrene monomer) by GPC-MALLS: the Mn of initial chain is 1,070 g/mol,with PDI 1.04; the Mn of resulting star is 89,900 g/mol, with PDI 1.31. The calculatedaverage number of branches is 40 (Note 16).

c. Star-block-linear-block-star polystyrene

1H NMR: δ 0.1 ppm (s, –Si–(CH3)2); δ 1.3-2.3 ppm (m, –CH(CH3)CH2CH3 and–CH(Ph)–CH2–); δ 6.4-7.2 ppm (m, Ph-H). 29Si NMR: δ -2.7 ppm (s, -(Ph)CH–Si(CH3)2-Ph); δ 5.2 ppm (s, -(Ph)CH–Si-CH(Ph)).

Molecular weight characterization data: the Mn of initial chain is 830 g/mol, PDI is 1.14;the Mn of living star is 6,400 g/mol with PDI 1.22, the calculated average number ofarms is 6.6 (Note 17); the Mn of star-block-linear diblock is 11,600 g/mol with PDI 1.11;the Mn of the triblock is 19,900 g/mol with PDI 1.12, which contains about 17 wt-%diblock residue; after fractionation, the Mn is 27,200 g/mol with PDI 1.02. Themeasured intrinsic viscosity is 0.12 dL/g, the calculated contraction parameter g’ is0.577 and the measured glass transition temperature is 92°C.


d. Radially linked star-block-linear polystyrene, ((PS)nPS)m

1H NMR: δ 0.1 ppm (s, –Si–(CH3)2); δ 1.3-2.3 ppm (m, –CH(CH3)CH2CH3 and–CH(Ph)–CH2–); δ 6.4-7.2 ppm (m, Ph–H). 29Si NMR: δ -2.7 ppm (s,-(Ph)CH–Si(CH3)2-Ph);

Molecular weight characterization data: the Mn of initial chain is 980 g/mol with PDI1.10; the Mn of living star is 2,800 g/mol with PDI 1.24 and calculated average numberof arms 2.6; the Mn of star-block-linear diblock is 10,600 g/mol with PDI 1.02; the Mn ofradially linked star-block-linear polystyrene is 53,100 g/mol with PDI 1.21 andcalculated average number of arms 4.9. After fractionation, the Mn is 70,200 g/molwithPDI 1.13 and the calculated average number of arms 6.5. The measured intrinsicviscosity is 0.18 dL/g, the calculated contraction parameter g’ is 0.43 and themeasured glass transition temperature is 100°C.

3.Notes

1. THF was dried over sodium metal, then distilled from sodium benzophenoneketyl under argon immediately prior to use.

2. p-Chlorostyrene was distilled from calcium hydride under vacuum. 3. Styrene was washed with 10% sodium hydroxide water solution, then washed

with DI water until neutral pH. The styrene was then dried with calcium chloride,stirred over calcium hydride for 24 hours, and distilled under vacuum just prior touse.

4. Cyclohexane was stirred with sulfuric acid at room temperature for 24 hours,then washed with water until neutral pH. The cyclohexane was refluxed withsodium metal for 24 hours, and distilled under argon just prior to use.

5. The slow addition of coupling agent was performed by using a gas-tight syringe,and the addition rate was controlled by using a syringe pump (KD Scientific,Model 100).

6. The number of arms of the living star can be controlled by the amount ofCDMSS added. To form an f-armed living star, (1 - 1/f) of the stoichiometricamount of CDMSS is needed, and the resulting living anion concentration istherefore 1/f of the initial concentration of living anions.5

7. The detailed fractionation procedure is as follow: 3.5 g sample was dissolved in180 mL toluene. Methanol was then added drop-wise until the solution becameslightly turbid. Another 2 – 3 mL methanol were added beyond the cloud pointand the solution was subsequently warmed until it became clear. Upon slowcooling to room temperature, a concentrated layer containing high molecularweight component separated from the bulk solution. The concentrated layerwas carefully collected into a vial. This fractionation procedure was repeatedtwo more times on the bulk solution and the three concentrated layers werecombined for further fractional precipitation. This whole procedure was repeatedto remove more low-molecular-weight component. The three new concentratedlayers were combined and carefully separated into three fractions by this


fractional precipitation method and the middle fraction was used as purepolystyrene star-block-linear-block-star triblock sample. The mass recovery ofpure star-block-linear-block-star triblock was 23%. Total mass recovery wasover 90%.

8. The fractionation of ((PS)nPS)m polystyrene was done by usingtoluene/methanol as solvent/non-solvent pair to remove low-molecular-weightcomponents, similar to that described in Note 7. Yields were improved byadjusting proportions of solvent/non-solvent accordingly.6

9. Determined by using a 1.0 mL volumetric flask calibrated with water, toluene,and methanol.

10.The 1H NMR spectroscopy was performed on samples dissolved in deuteratedchloroform on a Chemagnetics CMX Infinity 400 instrument.

11.The 29Si NMR spectroscopy was performed on samples dissolved in deuteratedchloroform on a Chemagnetics CMX Infinity 400 instrument. A small amount ofCr(acac)3 (~0.1 wt-%) was used to decrease the long spin-lattice relaxationtimes.8, 9 Sample concentrations of polymers were approximately 150 mg/mL inCDCl3. Other measuring conditions were a frequency of 79.48 MHz, sampletube spinning speed of 15 Hz, pulse delay of 15 second, with a total number ofscans of 2048.

12.Gel permeation chromatography with multi-angle laser light scatteringdetection, GPC-MALLS, was performed on a Hewlett-Packard model 1084Bliquid chromatograph equipped with two Hewlett-Packard Plgel 5µ Mixed-D(linear molecular weight range 200 – 400,000 g/mol) columns or a set of one 5µMixed-D column combined with one 5µ Mixed-C (linear molecular weight range200 – 2,000,000 g/mol ) columns. A calibrated RI (Waters R401) detector and aWyatt Technology miniDAWN detector (λ = 690 nm at three detector angles45°, 90° and 135°) were used. Elutions were carried out at ambient temperaturewith THF as solvent and a flow rate of 0.70 mL/min or 1.0 mL/min. Therefractive index increment (dn/dc) used for the polystyrene samples is 0.193mL/g.2

13.The average number of generations (G) of the resulting hyperbranched core ofthe star-shaped polystyrene was calculated using the equation

where Mstar is the molecular weight of star-shaped polystyrene, Minitial is themolecular weight of the initial polystyrene chain, and Mbranch is the molecularweight of the CDMSS residue (161 g/mol). The number of arms of the star-shaped polystyrene is equal to 2G.

14.The intrinsic viscosity was measured in THF at 30°C using a #50 Cannon-Ubbelohde viscometer. At least four different concentrations of each samplewere measured. The reduced viscosity and the inherent viscosity were plottedto zero concentration to obtain the intrinsic viscosity as the average of the twointercepts.

15.The glass transition temperature (Tg) was measured on a Perkin-Elmer DSC-7instrument running Pyris software. The sample was dried under vacuum at


100°C for 24 hours. Heating rate was 10°C/min and the measurement wascarried out under nitrogen purge. Tg was taken at the midpoint of the heatcapacity change as determined by the baseline tangents.

16.Determined by using a modified calculation equation as described in Note 13,where Mbranch is equal to the molecular weight sum of the CDMSS residue (161g/mol) and 10 styrene molecules (104.15 g/mol X 10).

17.The average number of arms of the living star, f, was calculated usingequations

and f=2G, where Mstar is the molecular weight of the living star, Minitial is themolecular weight of the initial polystyrene chain, and Mbranch is the molecularweight of the CDMSS residue (161 g/mol).

4.References

1. Department of Chemistry and Geochemistry, Colorado School of Mines, GoldenCO 80401.

2. Knauss, D. M.; Al-Muallem, H. A.; Huang, T.; Wu, D. T. Macromolecules 2000,33, 3557-3568.

3. Kawakami, Y.; Miki, Y.; Tsuda, T.; Murthy, R. A. N.; Yamashita, Y. Polym-1982,14, 913-917.

4. Huang, T. Ph. D. Thesis 2002, Colorado School of Mines, pp181-190 (2002).5. Knauss, D. M.; Huang, T. Macromolecules 2002, 35, 2055-2062.6. Knauss, D. M.; Huang, T. Macromolecules 2003, MA034108.7. Burchard, W. Advances in Polymer Science 1999, 143, 113-194.8. Freeman, R.; Pachler, K. G. R.; LaMar, G. N. J. Chem. Phys. 1971, 55, 4586-

4593.9. Williams, E. A. Annual Reports on NMR Spectroscopy 1983, 15, 235-289.

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