optically active hydrocarbon polymers with aromatic side chains, 4. stereospecific homo- and...

Die Makromolekulare Chemie 174, 15-25 (1974)

Istituto di Chimica Organica Industriale e Istituto di Chimica Organica della Facolta di Scienze M. F. N. della Universita di Pisa, Via Risorgimento 35, 56100 Pisa, Italy

Optically Active Hydrocarbon Polymers with Aromatic Side Chains, 4*)

StereospecXc Homo- and Copolymerization of Phenyl-a-olefins

CARLO CARLINI, FRANCESCO CIARDELLI, and DARIO PINI

(Date of receipt: May 17, 1973)

SUMMARY: The polymerization of optically active phenyl-a-olefins, such as (R)-4-phenyl- I-hexene

(1) and (S)-5-phenyl-l-heptene (2), has been performed by TiCl,/("ARA") or VCt4/ AI[CHzCH(CH3)z]3 catalyst. 2 gives polymers which are amorphous at room temperature; no evidence of stereoregularity is obtained by IR investigation, whereas 'H-NMR spectra seem to give some indication of steric order. By contrast, the polymers from 1, which are largely insoluble in boiling solvents, are crystalline at X-ray examination according to an isotactic structure. The copolymerization of 1 with 4-methyl- I-pentene (3) gives statistical copolymers which appear to be coisotactic. This is confirmed by crystallinity at X-ray examination, IR and optical activity data.

ZUSAMMENFASSUNG: Die Polymerisation von optisch aktiven a-Olefinen, wie (R)-CPhenyl-I-hexen (1) und

(S)-5-Phenyl-l-hepten (2), mit ZIEGLER-NATTA-KatalySatOren wie TiCl,/(,,ARA") oder VC14/AI [CH2CH(CH&] wird untersucht. 2 liefert Polymere, die bei Raumtemperatur amorph sind; kein Beweis sterischer Ordnung wird durch IR-Untersuchung erhalten, aber H-NMR-Spektren zeigen die Anwesenheit einer partiellen Stereoregularitat an. Im Gegen-

satz dazu liefert 1 Polymere, die in siedenden Lijsungsmitteln vorwiegend unloslich sind und die nach den Rontgendiagrammen kristallin sind, was auf das Vorhandensein von isotakti- schen Strukturen hinweist. Durch die Copolymerisation von 1 mit 4-Methyl-1-penten werden kristalline Polymere erhalten, die wahrscheinlich statistische coisotaktische Struktur be- sitzen, wie mit Hilfe der Rontgendiagramme der IR-Spektren und des Drehungsvermogens gezeigt wird.

Introduction

Following our investigation of the stereospecific polymerization of chiral cr-olefins by ZIEGLER-NATTA catalysts ' I , we have examined the homo- and copolymerization of optically active x-olefins containing the phenyl group

*) Paper 3: F. CIARDELLI, P. SALVADORI, C. CARLINI, E. CHIELLINI, 1. Am. Chem. SOC. 94, 6536 (1972).

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C. CARLINI, F. CIARDELLI, dnd D. PINI

directly bound to the asymmetric carbon atom’), such as (R)-4-phenyl-l- hexene (1) and (S)-5-phenyl-l-heptene (2).

FH = CH, YH=CH2 YH = CH2

The main aim of this work was to synthesize optically active stereoregular vinyl polymers containing the phenyl group in the side chain and having a simple structure which could be easily investigated also by simple conformational analysis 3 * ‘). In this paper the structural characteristics of the homopolymers of monomers 1 and 2 and the copolymers of 1 with 4-methyl-1-pentene (3) are reported. The investigation of the relationship between conformation and chiroptical properties in solution of these polymers are subject of another paper 5 ) .

Results and Discussion

Polymerization experiments

1 and 2, having optical purity larger than 90 %, were obtained as previously reported ’). Polymerization experiments were performed in the presence of heterogeneous ZIEGLER-NATTA catalysts obtained by reacting TiC1, PARA”) or VCl, with aluminum triisobutyl, mole ratio 1 to 3-4 (Tab. 1).

Tab. 1. Polymerization of (R)-4-phenyl-l-hexene (1) and (S)-5-phenyl-l-heptene (2) by MtCl./AI[CH2CH(CH3)2]3 catalystss)

Monomer MtCl, Solvent Dura- Temp. %Con-

in mmol in mmol t/h TPC sionb) Run type amount type amount type v/cm3 tion ver-

4H1 1‘) 3,12 TiCI,(“ARA”) 0,432 2,2,4-trimethyl- 4 280 60 26,6 pentane

4H2 Id) 6,31 VCI4 0,381 heptane 7 504 60 27,9

5H 2‘) 5,86 TiC13 (“ARK’) 0,724 2,2,4-trimethyl- 5 110 25-60 663 pentane

a) The mole ratio AI[CH2CH(CH3)2]3/MtCl, was 4,l; 3,3 and 3,O for the runs 4H1,4H2 and

b, Calc. as (Wt-solid polymer/Wt-starting monomer) ,100. ‘) Optical purity 94-97 %. c, Optical purity 90-92 %.

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5H, respectively; Mt = metal.

d, Optical purity 88-91 %.

Optically Active Hydrocarbon Polymers with Aromatic Side Chains, 4

These catalytic systems have been shown to produce no racemization in the polymerization of chiral aliphatic a-olefins I ) . Moreover they are isospecific in the polymerization of 3-phenylpropene (allylbenze.ie) 6 * 7), 4-phenyl-l-b~- tene6*7) and 5-~henyl-l-pentene~*~) and of some tolyl a-olefins8). 1 has a markedly lower reactivity than 2 as shown by conversion (Tab. 1); this is probably due to the larger steric hindrance around the double bond of 1. In fact the bulkiness of the substituent strongly affects the polymerization rate of branched cc-olefins in the presence of ZIEGLER-NATTA catalytic systems g). This is substantially confirmed by the high yield of polymeric products obtained in the copolymerization of 1 with 3 (Tab. 2). In fact in the presence of VCl,/ Al[CH,CH(CH,),], catalyst two mixtures of 1 and 3 with mole ratios of 1,4 and 0,7 have been converted into polymeric products up to more than 85 %.

Tab. 2. Copolymerization of (R)-4-phenyl-l-hexene (1) and 4-methyl-1-pentene (3) by VC14/Al[CH2CH(CH3)2]3 catalysta)

Comonomers VC14 Duration Temp. %Con- Run 1 3 version b,

amount amount amount in mmoI9 in mmoI in mmol tlh T/OC

HPl 12,2 8,57 1,25 161 25 85,3

HP2 6,25 8,86 0,834 161 25 93,9

Mole ratio AI[CH2CH(CH3)2]3/VC14 = 3,3 , solvent 10 cm3 of heptane. Calc. as (Wt-solid polymer/Wt-starting comonomers) .loo. Optical purity 88-91 %.

Structural characterization of the polymers

The polymer obtained from 2 gives by extraction with acetone, diethyl ether and cyclohexane in that order three fractions, which are amorphous at room temperature. No residue was found in this extraction (Tab. 3).

Tab. 3. Physical properties of fractions of poly[(S)-5-phenyl-l-heptene] (Run 5H)

Fraction extracted % of total [alLs”) 10-2. [q]b’ with weight cm3 g-I

Acetone 10,5 +23,6 - C )

Diethyl ether 61,8 +26,6 1,28 Cyclohexane 27,l +23,8 2,80

a) In cyclohexane, I = 1 dm. b, in benzene at 30°C. c, Not determined.

17

C. CARLINI, F. CIARDELLI, and D. PINI

It is known that this procedure gives fractions with different stereoregularity O).

No appreciable differences, however, were observed in the IR spectra of the three fractions which show the same bands with the same relative intensity. As an example in Fig. 1 the IR spectrum of the polymer extracted with cyclohexane is reported which is in agreement with the head to tail structure already proposed6* ’) for 4-phenyl-1-butene and 5-phenyl-1-pentene.

I I

Wavenurnber in cm? 4000 3ooo 2000 1600 1200 800 400

Fig. 1. IR spectrum of a film of poly[(S)-5-phenyl-l-heptene] (cyclohexane sol., diethyl ether insol. fraction)

In spite of the absence of crystallinity - it is of interest to remind that poly(5- phenyl- 1-pentene) 6, shows crystallinity only after laborious thermic treatment - it seems reasonable to assume that poly [(S)-5-phenyl-l-heptene] is also at least partially isotactic. This is confirmed by the lH-NMR spectra of the three

d-1 PPrn

Fig. 2. 1 0 0 MHz ‘H-NMR of fractions of poly[(S)-5-phenyl-l-heptene] in hexachloro-1,3- butadiene at 13OoC. (A): Cyclohexane sol. diethyl ether insol. fraction; (B): acetone sol.

fraction

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fractions at 100 MHz which show a much better resolution'l) of the peaks going from the firstly extracted fraction to the last one (Fig. 2), even if the viscosity of samples increases in that order. In addition the line width of the triplet of the methyl group at 6 = 0,73 ppm markedly decreases with the same trend according to an increase of stereoregularity going from the cyclohexane to the acetone extracted fraction. The obtainment of three fractions by solvent extraction, however, could also be attributed, at least in part, to the different average molecular weight of the macromolecules in each fraction. These fractions do not show appreciably different rotatory power (Tab. 3) as observed for fractions with different tacticity, but it must be considered that the asymmetric carbon atom in the polymers from 2 is not very close to the main chain 3).

Quite different properties are shown by the polymers obtained from 1. The polymer prepared by the TiC13/A1R3 catalyst was extractable by CHC13 only up to 10 %, whereas almost 50 % of soluble polymer was obtained in the presence of VC14/A1R3 (Tab. 4).

Tab. 4. Physical properties of fractions of poly[(R)-4-phenyl-l-hexene]

Run 4H 1 4H2

Fraction extracted % of the [u]26"' % of the [ u ] ~ ~ " ) Melting rangeb) with total weight total weight TIa C

Acetone - - 18,s --41,3 amorphous Chloroform 10,2" -6 1,6 31,9 -65,4 250-260 Residue 89,8 c, -d) 49,3 -6) 260-270

a) In chloroform; I = 1 dm. b, Determined with a KOFLER hot-plate polarizing microscope. c, After treatment with boiling decalin. d, Not determined.

In both cases the residue of the chloroform extraction was insoluble in the usual organic solvents including decalin at the boiling point. Because of the small amount of polymer available, the X-ray diffraction spectrum was performed on the crude polymer which appeared to be moderately crystalline (Fig. 3A). The weight of the fractions obtained by solvent extraction of the crude polymer, however, was sufficient for spectroscopic investigations and other measurements, particularly in the case of the run 4H2 performed in the presence of the VC14/AlR3 catalyst.

In Fig. 4 the IR spectra of the two fractions extracted with acetone and chloroform as well as of the residue are reported. The acetone extracted frac-

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Fig. 3. X-ray diffraction pattern of poly- [(R)-4-phenyl-l-hexene], crude polymer from run 4H2 (curve A) and of (R)-4-phenyl-l -hexene/4-methyl-l -pentene copolymer, fraction extracted with cyclohexane from run HPl (curve B)

2 eo

Y

I I I

1800 1600 1400 1200 1000 800 600 Wavenurnber in crn-'

Fig. 4. IR spectra of films of poly[(R)-4-phenyl-l-hexene] fractions. (A): Acetone sol. fraction; (B): chloroform sol., acetone insol. fraction; (C): residue of the chloroform extraction

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tion shows significant differences with respect to the others which have prac- tically the same spectrum. These last in fact show bands at about 865 and 805 cm-' which are lacking in the acetone fraction; moreover the bands at about 1095, 578, and 529 cm-l are much less intense than those of the acetone insol. fractions. The ratio of optical densities D109s/D1029 (base line points 1230 and 930 cm-'), D578/Ds56 and D529/Dss6 (base line points 635 and 478 cm-l) are 0,33, 1,00, and 0,73, respectively, for the acetone soluble polymer. Markedly higher values are found for the other two fractions. In fact the above three ratios are 0,40, 1,24, and 1,27 for the fraction of the CHC13- extraction and 0,42,1,18, and 1,43 for the residue. Moreover, the last two fractions show, at the hot-plate microscope, rather a high melting range, whereas the fraction of the acetone extraction is amorphous at room temperature (Tab. 4).

The higher optical rotation of the fraction of the chloroform extraction is a further indication of the higher stereoregularity 3, with respect to the acetone soluble polymer. No evidences exist that the residue of the solvent extraction is remarkably more stereoregular than the chloroform soluble, acetone insoluble polymer. The extremely low solubility could be in fact related with the higher molecular weight. Accordingly, in the case of poly [(S)-3-methyl-l-pentene] 3,

only the macromolecules with [q] < 50 cm3 8-l have been dissolved with boiling solvents. However, it can be expected, that this residue is at least moderately more stereoregular than the chloroform soluble, acetone insoluble polymer.

Structural characterization of 4-methyl-I-pentene ( 3 ) /(R) -4-phenyl-l-hexene (1) copolymers

As reported in Tab. 2, two runs HP1 and HP2 of copolymerization have been performed, the mole ratio 1 to 3 being 1,4 and 0,7, respectively. The high conversion in both cases does not allow to draw any conclusion about the relative reactivity of the two monomers. Considering the homopolymerization rate of 1 and 3, however, the latter appears to be more reactive according to the minor steric hindrance around the double bond9). In any way, the type of catalyst used allows to predict the formation of a substantially statistic copolymer 12), even if formation of blocks of the homopolymer is expected, because of the different reactivity of the two comonomers. The formation of a substantially statistic copolymer is confirmed by the fractionation of the methanol insoluble polymeric products with boiling solvents and by the properties of the fractions thus obtained (Tab. 5). The first indication of copolymer formation is given by the relative amount of polymer extracted with each of the following solvents used in that order acetone, ethyl acetate, diethyl ether, cyclohexane, chloroform and toluene. No residue of the toluene extraction

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Tab. 5. Physical properties of fractions of (R)-4-phenyl-l-hexene (1)/4-methyl-l-pentene (3) copolymers

Run HP1 HP2

Fraction % of total [alga) % units % of total [ ~ ] 2 , ~ " % units extracted with weight from 1 weight from 1

Acetone 2,7 -66,5b' 25,9 3 2 -70,9b' 30,9 Ethyl acetate 39,l -114 47,O 35,7 -114 36,6 Diethyl ether 7,9 -91,o 19,7 14,6 -105 20,3 Cyclohexane") 21,6 -80,9 26,4 28,7 -80,4d' 17,8 Chloroform") 17,7 -86,l 80,3 16,l -69,6 79,3 Toluene 1 l,o C ) C) C) C ) 1,7

*) In chloroform, if not differently specified, I = 1 dm. b, In heptane. c, [q] in tetralin at 120°C higher than 100 cm3 g-l.

c, Not determined. In carbon tetrachloride.

was obtained, thus excluding the presence of homopolymer from (R)-4-phenyl- 1-hexene; moreover, the whole product appears to be extractable with oxygen containing solvents to a larger extent than poly[4-methyl-l-pentene] 13) . In fact it is well known that the copolymer of two comonomers giving crystalline homopolymers, has a lower melting point and a higher solubility than the corresponding homopolymers 4). The determination of the chemical composition of the fractions, performed by lH-NMR (s. Experimental Part), shows the presence of both comonomers in each fraction according to copolymer formation. Moreover, the optical activity indicates a complex dependence on the composition and does not linearly depend on the amount of optically active comonomer 1. This can be explained by assuming that also the units from 3 are optically active as a consequence of their inclusion in stereoregular macromolecules with an optically active comonomer s* 13). The X-ray examination shows, that the fractions not extractable with boiling ethyl acetate are at least partially crystalline and the fractions containing more than 50 % of units from 3 exhibit the diffraction peaks characteristic of isotactic poly [4-methyl-1- pentene] 15), but the peaks of poly[4-phenyl-l-hexene] are also present (Fig. 3B).

In the IR spectra of these last fractions, when containing more than 50 % of units of 3, the band at 995cm-' is present, typical of isotactic poly[4- methyl-1-pentene] ' 6), thus demonstrating the isotactic enchainment of these monomeric units. The values of the optical density ratio D995/D91,'6) are in fact around 0,5 very close to the value found for isotactic poly[4-methyl-l- pentene].

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Conclusions

Optically active a-olefins, having a phenyl group bound to the asymmetric carbon atom, can be polymerized by ZIEGLER-NATTA catalysts to optically active polymers.

When the asymmetric carbon atom is in y-position to the double bond, the polymerization occurs easily with high yield. The polymer formed is amorphous at room temperature, whereas 5-phenyl-1-pentene 6 , and 5-methyl-1-heptene ') give moderately crystalline polymers. These data, however, do not allow to exclude the presence of stereoregularity in poly[(S)-5-phenyl-l-heptene] ; in fact isotactic amorphous polymers are known 17). Furthermore, the polymerization of vinyl monomers, having the asymmetric carbon atom in y-position, has been recently shown to be not stereoselective Is) and the absence of crystallinity could be due to the copolymerization of the S antipode with the R one, which is present up to 4-5 % in the polymerized monomer.

The polymerization of 1, under the same conditions, yields on the contrary crystalline polymers. The lower yield obtained shows, that in this case steric interactions occur between active sites and the monomer side chain as found for P-branched-a-olefins g ) . Evidence of stereoregularity is given also by IR spectra. 1 gives with 4-methyl-1-pentene partially crystalline statistic copolymers. X-ray examination and IR spectra indicate that in the copolymer macromolecules the units from 3 are enchained in an isotactic way. Therefore, considering the catalytic system used, which is isospecxc in the polymerization of w-phenyl-a-olefins 6 , and of chiral aliphatic a-olefins I), it seems likely that also the units from 1 are included in isotactic blocks. A similar situation is very probably true in the case of the crystalline homopolymer of 1. Support to these conclusions is given by optical activity data which are discussed in details in the next paper 5 , in which relationships between chiroptical properties and conformational and configurational regularity are reported.

Experimental Part Materials:

Monomers: (R)-4-Phenyl-l-hexene (1) 2): Two samples, purified by preparative gas liquid chromatography (g.l.c.), have been used having bp,, 9O-9l0C, n&5 = 1,4987, d:* = 0,8753, [a]hs(neat) = -8,43 and -8,99 (optical purity 88-91 and 94-97 %, respectively).

(S)-5-phenyl-l-heptene (2) l): The used sample, purified by preparative g.l.c., had bp,,- 103--104"C, ng = 1,4958, di5 = 0,8708, [a]g (neat) = +4,80 (optical purity 90-92 %) 4-methyl-1-pentene (3) from Fluka was treated on Na/K alloy under nitrogen and distilled before use.

Catalyst: All the catalyst components were handled under dry nitrogen.

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VCI4 from “Stauffer” was purified by distillation immediately before the use. A1 [CH,CH(CH,),], from “Texas Alkyls” was isolated from the hexane solution by

TiCI3 (“ARA”) from “Stauffer” was used without further purification.

Melting points were determined on a Kofler hotplate polarizing microscope.

removing the solvent under vacuum and then distilling at 0,l mbar.

Polymerization experiments:

Polymerization and copolymerization experiments were carried out in a similar way in glass vials, under dry nitrogen. The following runs are described in details:

Polymerization of (Rl-4-phenyl-I-hexene (1) by TiC13 (“ARA”IIAI[CHZCH(CH~),]~ catalyst (Run 4HI) : To 0,067 g (0,432 mmol) of TiCI3 (“ARK’), suspended in 4 cm3 of anhydrous heptane, was added dropwise at room temp. 0,346g (1,75mmol) AI[CH2CH(CH,),],. After aging the catalyst at 50°C for ten min, 0,5 g (3,12 mmol) of 1, having [a]? = -8,99, was added at room temp. The vial was sealed and kept at 60°C for 300 h. The polymerization was interrupted by treating the reaction mixture with boiling methanol. The solid polymer was purified with dilute HCI, filtered and dried i . vac. to give 0,132 g.

Polymerization of (S ) -5-phenyl- I -heptene (2) by TiCI, (“A R A ” ) IAIICH, CH ( CH, ) I , catalyst (Run 5H): To 0,112 g (0,724 mmol) of TiCI,(“ARA”), suspended in 5 cm3 of anhydrous 2,2,4-trimethylpentane, were added dropwise at room temp. 0,433 g (2,19 mmol) AI[CH2CH(CH3)2]3 and 1,02 g (5,86 mmol) 2 having [a]g = +4,80. The vial was sealed and stirred for 90 h at room temp. and for 20 h at 50-60°C. The polymerization was stopped by treating with boiling methanol. The recovered polymer, purified by dry HCl in diethyl ether and successive precipitation with methanol, was filtered and dried i. vac. to give 0,6814 g.

Copolymerization of (R)-4-phenyl-l-hexene (1) with 4-methyl-I-pentene (3) by VCl,/ A I / C H ~ C H ( C H 3 ) ~ l ~ catalyst (Run H P l ) : To 10 cm3 of anhydrous heptane were added at room temp. 0,819 g (4,13 mmol) A1[CH2CH(CH3),], and 0,251 g (1,25 mmol) VCI4 in that order. After aging the catalyst at room temp. for 10 min, a mixture of 1,95 g (12,2 mmol) of 1 ( [a]&s = -8,43) and 0,72 g (8,57 mmol) 3 were added. The vial was sealed, then kept at room temp. for 161 h. The polymerization was interrupted as above reported and 2,5487 g of purified solid polymer was obtained.

Polymer Characterization:

Fractionation: The polymers were fractionated by boiling solvents in Kumagawa extrac- tors lo).

IR Spectroscopy: IR examination of polymer fractions was performed by a Perkin Elmer Model 225 spectrophotometer on thin films prepared by evaporating polymer solutions or by pressing polymer powder at high temp. under nitrogen.

Polarimetry: Optical rotatory measurements were carried out by a Schmidt-Haensch Lip- pich polarimeter or by a Perkin Elmer Model 141 spectropolarimeter with a sensibility of i 0,005” and 0,003’, respectively. Chloroform or cyclohexane polymer solutions having a concentration in the range of 4-22 mg cmW3 were used.

X-Ray diffraction patterns: These were performed at room temp. with a Philips Model PW lOlO/25 diffractometer.

Viscometry: Intrinsic viscosity was determined at 30°C in benzene or at 120’C in tetralin by a Desreaux-Bischoff dilution viscometer.

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'H-NMR Spectroscopy: 'H-NMR spectra, to determine the copolymer composition, were obtained by a Varian T-60 spectrometer in CC14-solutions with TMS as internal standard. The spectra on the homopolymers were carried out at 130°C in hexachloro-1,3-butadiene by a Jeol J-NM 100 spectrometer. The chemical shifts are also referred to TMS.

The authors wish to thank Mr. P. G. VERGAMINI for performing IR spectra and Dr. R. MENICAGLI for kind supply of (R)-4-phenyl-l-hexene and (S)-5-phenyl-l-heptene samples. The financial support from the CONSIGLIO NAZIONALE DELLE RICERCHE (Roma) is gratefully acknowledged.

') F. CIARDELLI, G. MONTAGNOLI, D. PINI, 0. PIERONI, C. CARLINI, E. BENEDETTI, Makro- mol. Chem. 147, 53 (1971). L. LARDICCI, R. MENICAGLI, P. SALVADORI, Gazz. Chim. Ital. 98, 738 (1968).

3, P. PINO, F. CIARDELLI, G. P. LORENZI, G. MONTAGNOLI, Makromol. Chem. 61,207 (1963). 4, P. PINO, F. CIARDELLI, M. ZANDOMENEGHI, Ann. Rev. Phys. Chem. 21, 561 (1970). ') C. CARLINI, F. CIARDELLI, L. LARDICCI, R. MENICAGLI, Makromol. Chem{174,27,(1973). 6, G. PREGAGLIA, M. BINAGHI, Gazz. Chim. Ital. 90, 1554 (1960). ') A. V. TOPCHIEV, V. N. ANDRONOV, G. I. CHERNYI, Neftkhim. 3, 725 (1963); C.A. 62,

') J. A. PRICE, M. R. LYTTON, B. G. RANBY, J. Polymer Sci. 51, 541 (1961). 9, J. BOOR, JR., Pure Appl. Chem. 8, 57 (1971).

637g (1963).

lo) G. NATTA, P. PINO, G. MAZZANTI, Gazz. Chim. Ital. 87, 528 (1957). 11) F. A. BOVEY, Accounts Chem. Res. 1, 175 (1968).

See for instance: C. A. LUKACH and H. M. SPURLIN in: Copolymerization, editor G. E. HAM, Interscience Publ., New York 1964, p. 138 and 142.

13) C. CARLINI, F. CIARDELLI, P. PINO, Makromol. Chem. 119, 244 (1968). 14) R. B. ISAACSON, I. KIRSCHENBAUM, I. KLEIN, J. Appl. Polymer Sci. 9, 933 (1965). 15) F. E. KARASZ, H. E. BAIR, J. M. O'REILLY, Polymer 8, 547 (1967). 16) P. BORRINI, Thesis, University of Pisa, July 1968. ") G. NATTA, Makromol. Chem. 35, 93 (1960). '') E. CHIELLINI, M. MARCHETTI, Makromol. Chem. 169, 59 (1973).

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optically active hydrocarbon polymers with aromatic side chains, 4. stereospecific homo- and...

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