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Polymer Degradation and Stability 98 (2013) 951e957

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Polymer Degradation and Stability

journal homepage: www.elsevier .com/locate /polydegstab

Thermal and surface characteristics of some b-cyclodextrin-based side-chainazo amphiphilic polyurethanes

D. Filip*, D. Macocinschi, L.M. Gradinaru“Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica 41 A, 700487 Iasi, Romania

a r t i c l e i n f o

Article history:Received 15 January 2013Received in revised form18 February 2013Accepted 25 February 2013Available online 5 March 2013

Keywords:Poly(ether urethanes)b-CyclodextrinAzo chromophoreThermogravimetrySurface properties

* Corresponding author. Tel.: þ40 232217454; fax:E-mail address: dare67ro@yahoo.com (D. Filip).

0141-3910/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.polymdegradstab.2013.02.0

a b s t r a c t

New amphiphilic azo aromatic b-cyclodextrin poly(ether urethanes) with different soft segment lengthshave been synthesized and characterized. The thermal stability and kinetic parameters of the synthe-sized polyurethanes by using thermogravimetry (TG) and derivative thermogravimetry (DTG) underdynamic conditions of temperature, were evaluated. The non-isothermal kinetic parameters of thethermal degradation (activation energy, order of reaction, pre-exponential factor) were discussed interms of the integral methods: CoatseRedfern, FlynneWall, van Krevelen and UrbanovicieSegal. TheReicheLevi method was also employed in evaluation of variation of the kinetic parameters with con-version. Surface parameters were evaluated based on contact angle determinations. Surface-free energyvalues and the polar and dispersive components were obtained by applying the OwenseWendteRabeland the Kaelbe methods.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The development of environmentally-friendly and biodegrad-able polymers for various applications has gained significantattention in recent years in academia and industry.

Excellent properties and wide applications of thermoplasticpolyurethanes combined with the potential biocompatibility andbiodegradability of natural raw materials stimulated scientists tosynthesize biopolyurethanes. Thermal characterization of poly-urethanes based on renewable resources is very important tomonitor their thermal stability and biodegradability behaviour [1e5]. Numerous studies have been carried out on the thermaldegradation of polyurethanes [6e10] and it was found that the twostages of degradation of polyurethanes are in connection with thedegradations of the hard and soft segments respectively. The initialstage of thermal degradation is governed by urethane bonddecomposition leading to the formation of primary amine andolefin or secondary amines and carbon dioxide [11,12]. Onset ofthermal degradation of polyurethanes depends on type of isocya-nate and glycol used: for polyurethane synthesized from aromaticisocyanate and aliphatic glycol the degradation starts at about220 �C [13,14]. The thermal stability of more complex systems like

þ40 232211299.

All rights reserved.17

segmented polyurethanes depends on their morphology, on theurethane groups per unit volume, segment length and concentra-tion. Oxidative process plays a major role in the decomposition ofether-based polyurethanes. Poly(ether urethanes) are more hy-drolytically stable than poly(ester urethanes). Poly(ester urethanes)are more thermally stable than poly(ether urethanes) andpolyurethaneeureas are more stable than polyurethanes [6e10].The branching and cross-linking lead to increased thermal stabilityof polyurethanes [15].

Interfacial interactions, in many cases are more important thancomposition and morphology of bulk phases, and ultimately definethe molecular behaviour of the system. The ratio between thesurface hydrophilic and hydrophobic properties is related toenhanced biocompatibility of polyurethanes. Surface characteris-tics such as: distribution of electric charges, surface tension andhydrophobe/hydrophile balance confer to the material more or lessthrombo-resistant qualities [16].

Amphiphilic biodegradable polymers are receiving more andmore attention due to their wide application in biomedical uses[17,18]. Amphiphilic polymers which contain azobenzene groupscombine photoresponsive properties of azo polymers with self-assembling characteristics and can generate photosensitive mi-celles [19]. The photoresponsive properties of azo polymers arebased on the trans-to-cis and the cis-to-trans photoisomerization ofazobenzene leading to changes in their molecular shape and dipolemoments [20]. Cyclodextrins are natural occurring molecules

D. Filip et al. / Polymer Degradation and Stability 98 (2013) 951e957952

derived from starch. Cyclodextrins are cyclic oligosaccharides oftoroidal shape with an inner hydrophobic cavity and hydrophilicexterior, which are able to form hosteguest (inclusion) complexeswith variousmolecules. The synthesis of such structures is based onthe molecular recognition principle and is the result of cooperationof various noncovalent interactions [21,22].

In this work we report a new type of amphiphilic biodegradablepoly(ether urethanes) and their bulk thermal characterization andsurface properties investigation are presented.

The evaluation of thermal stability and kinetic parameters byusing thermogravimetry and derivative thermogravimetry underdynamic conditions of temperature along with the effects of thechemical structure on the surface properties of the synthesizedpoly(ether urethanes) are investigated. The non-isothermal kineticparameters of the thermal degradation of polyurethanes are eval-uated by using CoatseRedfern [23], FlynneWall [24] for constantheating rate [25], van Krevelen [26] UrbanovicieSegal [27], integralmethods. The ReicheLevi method [28] was also employed inevaluation of variation of the kinetic parameters with conversion.The global kinetic parameter values, used for comparative pur-poses, have been evaluated in the same conditions for all studiedsamples. On the basis of contact angle measurements the surface-free energy values and the polar and dispersive components wereobtained by applying the OwenseWendteRabel and the Kaelbemethods [29,30].

2. Experimental

2.1. Materials

Synthesis of monoazo-diol 4-[bis(2-hydroxyethyl)amino]-40-acetylazobenzene was carried out in a two-step procedure: diazo-tation of 4-acetylaniline followed by coupling with N,N-bis(b-hydroxyethyl)aniline [31], m.p. 159e160 �C.

1H NMR (DMSO-d6): d 2.6 ppm eCH3eCOe; d 3.6 ppm eCH2e;d 4.8 ppm eOH; d 6.9 aromatic protons ortho toeN<, d 7.8 aromaticprotons ortho to eN]Ne, d 8.1 aromatic protons ortho to eCOCH3.FT-IR: 3283 cm�1 eOH stretching; 2970e2800 cm�1 >CH2; eCH3stretching; 1664 cm�1 >C]O stretching; 1597 cm�1 aromatic e

CH<.Poly(ethylene glycol)-block-poly(propylene glycol)-block-

poly(ethylene glycol) (Pluronic L-61) was purchased from SigmaeAldrich, PEO2PPO30PEO2 (Mn 2000 g/mol); 4.40-diphenylmethanediisocyanate (MDI, Merck) was distilled prior to utilization underreduced pressure. Methylene dicyclohexyl diisocyanate (H12MDI)was purchased from Fluka and used as received; Polyethyleneglycol (PEG600) was purchased from SigmaeAldrichMn 600 g/mol;b-cyclodextrin (b-CD) (Fluka) was used without further purifica-tion. The polyurethanes were prepared by the typical two-stepsolution polyaddition using N,N-dimethylformamide (DMF, Flukap.a.) as a solvent. First, the NCO-terminated prepolymer was pre-pared by dehydrating the Pluronic L-61 or the mixture Pluronic L-61:PEG600 (1:1) for 3 h at 90 �C under vacuum followed by addingH12MDI or MDI to the vigorously stirred macrodiol. The amounts ofdiisocyanate, macrodiol and chain extender were kept at a molarratio 2:1:(0.7 azo dye þ 0.45 b-CD). The reaction between diiso-cyanate and macrodiol took place for 2.5 h under nitrogen atmo-sphere at 90 �C in the presence of dibutyltin dilaurate (95%, Aldrich)as a catalyst. The temperature was lowered to 70 �C and the chainextender (azo dye), was added. The reaction continued for 1.5 h.After that b-CD was added and the reaction continued for 1.5 h atthe same temperature. The resulting polymers were precipitated inwater and dried under vacuum for several days. Characteristicsignals for the synthesized poly(ether urethanes) were found in the1H NMR and FT-IR spectra.

1H NMR (CDCl3) of polyurethane P2: d 1.4e1.8 ppm protons fromdicyclohexyl rings; d 1.1 ppm eCH3 (PPO); d 2.6 ppm eCH3eCOe;d 3.3e3.8 ppm eCH2eCH2eOe (PEO); >CHeCH2eOe (PPO);d 4.2e4.3 ppmeCH2eOeCOe; d 3.5e4.9 cyclodextrin protons; d 6.9aromatic protons ortho to eN<, d 7.8 aromatic protons ortho to e

N]Ne, d 8.1 aromatic protons ortho to eCOCH3.FT-IR: 3300e3400 cm�1 >NH and eOH stretching; 2800e

2970 cm�1 aliphatic group stretching; 1717 cm�1 >C]O urethanegroup stretching; 1595 cm�1 aromatic eCH<; 1108 cm�1 eCeOeCe stretching.

The chemical synthesis route of the studied amphiphilic poly(-ether urethanes) is presented in Scheme 1. FT-IR spectra of azo dyeand synthesized polyurethanes are depicted in Fig. 1.

2.2. Methods

Infrared spectroscopy (FT-IR) was performed on a VERTEX 7Instruments in the 600e4000 cm�1 spectrum range with a reso-lution of 2 cm�1 using thin films on KBr pellets.

1H NMR spectra were registered using Bruker Avance DRX 400Instrument (DMSO-d6, CDCl3).

The molecular weight was determined by using a GPC PL-EMD950 evaporative mass detector instrument (solution in DMF, 1%).

A PerkineElmer DSC-7 operated under nitrogen with a heating/cooling rate 10 �C/min was used for thermal analysis for samplesweighing 5e7 mg.

The thermal stability was determined in air on a DERIVATO-GRAPH Q-1500 D apparatus (Hungary) under the following con-ditions: TGA scans were gathered at a ramping rate of 10 �C/min forsample, with an initial weight of ca 50 mg in a 30e700 �C oftemperature range.

For contact angle measurements each of the polyurethanes wasdissolved in DMF, to reach concentration of 1 g/dL. The solutionswere cast on a glass plate and initially solidified by slow drying inDMF saturated atmosphere for 7 days and finally by drying at 50 �Cunder vacuum (48 h). The polyurethane films thus prepared weresubjected to surface analysis. Static contact angles were measuredat room temperature by the sessile-drop method with a CAM-101(KSV instruments, Helsinki, Finland) contact angle measurementsystem equipped with a liquid dispenser, video camera, and drop-shape analysis software. Double distilled water, ethylene glycol,diiodomethane were used as testing liquids. For each liquid threedifferent surface regions were selected to obtain a statistical result.

3. Results and discussion

3.1. Thermal characterization of the synthesized polyurethanes

In Table 1 molecular weights (Mn: number-average molecularweights; Mw/Mn: dispersity estimated from GPC) and glass transi-tion temperatures (Tg fromDSCmeasurements, second heating run)of the synthesized polyurethanes are presented. Fig. 2 shows theDSC thermograms (second heating run) of the studied poly(etherurethanes). The Tg found (secondheating run) for startingmacrodiolPluronic L-61 is �70.6 �C and the Tg found (second heating run) forstarting PEG600 is �75 �C. Generally for segmented polyurethanesTg value represents a measure of purity of soft segment regions;when there are hard segments dispersed in the soft domains orcrosslink between polyurethane segments Tg value is increased. Tgsfound for studied supramolecular polyurethane network systemswhich correspond to soft segment are higher due to the rigidityintroduced in the polymer matrix by b-cyclodextrin. In addition thelinkage (length of spacer) between side-chain azo chromophore andthe polymer backbone affects Tg (Tg becomes increased for shorterspacer length which causes a stronger coupling to the main chain)

Scheme 1. Chemical synthesis route of the studied amphiphilic poly(ether urethanes).

D. Filip et al. / Polymer Degradation and Stability 98 (2013) 951e957 953

and the motion of the azo group and thus their orientation andpacking. It is observed in Fig. 2 that the studied multiblock co-poly(ether urethanes) evidence broad glass transitions due totheir heterogeneous character determined by interaction betweenthe phases and morphology resulting there from. The glass transi-tion temperatures of poly(ether urethanes) basedonPEG600 co-softsegment are found lower. DSC thermograms reveal (Fig. 2) theabsenceofmeltingendotherms. Themacrodiol Pluronic L-61used inthe synthesis of polyurethanes is fully amorphous due to the highpercentage of PPO units. The PEG600 block of Mn z 600 in thepolyurethane network crystallizes very little or not at all. Moreover,due to the large steric configuration of b-cyclodextrin the crystalli-zation is easy to suppress.

The thermal characteristics obtained from TG (Fig. 3) and DTGcurves are tabulated in Table 2 and the temperature values atdifferent weight losses are tabulated in Table 3.

Fig. 1. FT-IR spectra of azo dye and synthesized polyurethanes.

The studied polyurethanes have at least two major stages ofdegradation. The temperature maximum peak (Tmax) in each stageof degradation corresponds to the degradation temperature of themaximum rate at this stage. The DTG curves of the studied poly(-ether urethanes) not only displaymaximum peaks (Tmax1 and Tmax2peaks) but also shoulder peaks (Ts) as presented in Table 2. The finaldecomposition stage can be attributed to the oxidation of poly-urethane decomposition products.

The global kinetic characteristics for the main degradation stageof overlapped processes are presented in Table 2. The evaluatedkinetic parameters, activation energy, order of reaction and pre-exponential factor by different applied integral methods showgood agreement. The onset degradation of polyurethanes which isgoverned by the decomposition of urethane hard segments is tak-ing place at temperatures higher than 260 �C. The decomposition ofpure b-cyclodextrin starts at around 260 �C [32]. The polyurethanesbased on aromatic diisocyanate such as MDI are more stable andgenerally show crystalline order of hard segments due to highsymmetry of the diphenyl methane unit (extended conjugation andstrong intermolecular interactions). It is evident that the initialtemperatures of decomposition are higher for MDI-based poly-urethanes P3, P4 than for polyurethanes P1, P2 based on H12MDI.The higher activation energies determined for P3 and P4 are indi-cating also higher thermal stability. It was found that the thermalstability of side-chain azo polymers decreased as the chromophoredensity increased due to increasing azo bond density [33]. Thevalues of order of reaction higher than one suggest degradation

Table 1Molecular weights, dispersity indices, glass transition temperatures of the studiedpoly(ether urethanes).

Polyurethane Mn Mw/Mn Tg, �C

P1 28,908 1.432 �45P2 53,280 1.699 �48P3 29,478 1.455 �38P4 36,675 1.431 �50

Table 2Thermal and kinetic characteristics of the synthesized poly(ether urethanes).

Sample Activation energy (kJ/mol)/order of reaction/ln A

CoatseRedfern FlynneWall van Krevelen UrbanovicieSegal

P1 260e470 �C; wt.a loss 67%; Tmax1 ¼ 330 �C; Tmax2 ¼ 400 �C114.8/1.6/16.2 114.9/1.5/16.5 147/1.7/22 112/1.5/15.8480e675 �C; wt. loss 18%

P2 265e525 �C; wt. loss 73%; Tmax1 ¼ 410 �C; Tmax2 ¼ 460 �C114/1.7/15 119/1.7/16.3 155/1.9/22.2 115.3/1.7/15.4525e685 �C; wt. loss 20%

P3 280e430 �C; wt. loss 63%; Tmax1 ¼ 335 �C; Tmax2 ¼ 385 �C146/1.6/22.6 149/1.6/23.3 181/1.7/29 148.7/1.6/23.17430e700 �C; wt. loss 26%

P4 285e430 �C; wt. loss 57%; Ts ¼ 350 �C; Tmax ¼ 380 �C154/1.5/23.9 156.5/1.5/24.5 187.7/1.6/30.18 152/1.4/23.5430e680 �C; wt. loss 30%

a Weight loss percentage corresponding to degradation stage.Fig. 2. DSC thermograms of the studied poly(ether urethanes) (second heating run,10 �C/min).

D. Filip et al. / Polymer Degradation and Stability 98 (2013) 951e957954

mechanisms more complex than diffusive processes whichaccompany usually thermal decomposition.

The non-isothermal thermal analyses can provide informationrelated to a wide temperature range and allow rapid determinationof the kinetic parameters. The processes involved in the thermaldegradation depend on conversion (a) and are included in a con-version function that can be written in its integral [23e28] or dif-ferential form [34e36]. The conversion function is time dependentand is represented by the reaction rate and includes a factordepending on temperature, named rate constant containing theactivation energy and the pre-exponential factor. Solid-state kineticmodels in their particular differential and integral forms of theconversion function were proposed to describe the degradationmechanisms [37].

The change of activation energy as a function of conversion wasfollowed by using the LevieReich kinetic analysis method [28] inorder to compare the thermal decomposition of the studied prod-ucts. Activation energy can be considered as a semi-quantitativefactor to characterize thermal stability. The values of reaction or-der employed in the calculation were those estimated from theCoatseRedfern method (Table 2). The dependence of activationenergy as a function of conversion for the main degradation stagefor the studied poly(ether urethanes) is plotted in Fig. 4. It can beseen that as the thermal decomposition process proceeded, theactivation energy remained unchanged or slightly changed after

Fig. 3. Thermogravimetric curves of the studied poly(ether urethanes).

the initial stage and then remained constant until a ¼ 0.6e0.7. Thisbehaviour suggests a single degradation mechanism [38] and thatthe stabilities of the intermediate products are similar. At the onsetof thermal degradation, weaker bonds are implicated, small mo-lecular fragments generating volatiles, and diffusion processesfaster than chemical reactions occur. The apparent energy values inconnection with thermal stability evidenced by Reich Levi curvesare consistent with the order of the studied polyurethanes statedby using the integral methods (Table 2).

The variations of the rate constant as a function of conversionfor the main degradation stage for the studied poly(ether ure-thanes) are plotted in Fig. 5. Figs. 4 and 5 show that the behaviour ofrate constant and activation energy is in agreement with Arrheniusequation. At low conversions the rate constant manifests an abruptincrease with increasing conversion and afterwards slightly in-creases or tends to remain constant.

The pre-exponential factor tends to be strongly correlated withthe activation energy via the “kinetic compensation effect”. Thelinear interdependence results from the interaction between themathematical nature of the Arrhenius-reaction rates and physico-chemical and experimental factors. Fig. 6 represented this inter-dependence between these two kinetic parameters for main stageof thermal degradation of studied poly(ether urethanes). The iso-kinetic parameters for this interdependence corresponding to themain degradation stage are given by: ln A ¼ mEa þ n; m ¼ 0.1978;n ¼ �6.7975; R2 ¼ 0.9845.

3.2. Contact angles and surface parameters

The surface tension is determined by using methods that arebased on contact anglemeasurements between the liquidmeniscusand the polyurethane surface. A contact angle below 90� indicatesthat the test liquid readily wets the substrates, while an angle over90� shows that the substrate will resist wetting. Table 4 lists thecontact angles between double distilled water, ethylene glycol, orCH2I2 and polyurethane samples.

The surface energy of the films was calculated using the Youngequation:

Table 3Temperature values (�C) at different weight losses (%).

Sample T10 T20 T30 T40 T50 T60

P1 318 342 362 383 397 412P2 346 368 390 404 415 435P3 326 348 365 386 397 494P4 335 352 369 383 399 468

Fig. 4. Variation of activation energy as a function of conversion (a) for studied pol-y(ether urethanes). Fig. 6. ln A versus E for thermal decomposition of main degradation stage of the

studied poly(ether urethanes).

D. Filip et al. / Polymer Degradation and Stability 98 (2013) 951e957 955

gLVcos q ¼ gSV � gSL (1)

where gSV is the surface energy, gSL is the solid-drop interfacialtension, gLV is the liquidevapour surface tension and q is the drop-surface contact angle [29,39,40]. The surface tension casn bedivided into two components, a polar component ðgp

SV;gpSLÞ

including two types of Coulomb interactions (dipoleedipole anddipole induced dipole) and a dispersive component ðgdSV;gdSLÞ rep-resenting van der Waals interactions [41]. The interfacial solideliquid tension is given by Fowkes [42]:

gSL ¼ gSV þ gLV � 2� ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

gdSVgdLV

qþ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffigpSVg

pLV

q �(2)

By combining with the Young equation, one obtains:

gLVð1þ cos qÞ ¼ 2� ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

gdSVgdLV

qþ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffigpSVg

pLV

q �(3)

The surface energy can be given as : gSV ¼ gpSV þ gdSV (4)

Fig. 5. Variation of rate constant as a function of conversion (a) for studied poly(etherurethanes).

The surface-free energy values (gSV) and the polar ðgpSVÞ anddispersive ðgd

SVÞ components were obtained by the OwenseWendteRabel and the Kaelbe methods [29,30]. The free energy ofadhesion of a polymer in contact with a liquid can be expressed bythe equation:

Wa ¼ 2� ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

gdSVgdLV

qþ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffigpSVg

pLV

q �(5)

Table 4 shows that the obtained results of contact angle (higherthan 90�) evidence the hydrophobic character of the studiedpolyurethanes due to soft segment (Pluronic L-61) which contains ahigh amount of PPO units which are very hydrophobic. Introduc-tion of the hydrophilic PEG600 co-segment determined thedecrease of contact angle. The contact angle for MDI-based poly-urethane sample (P3) is lower than that found for H12MDI poly-urethane sample (P1).

The results are related to the more or less restricted movementof the hard segment towards surface and may depend on type ofdiisocyanate used: H12MDI is highly flexible which is detrimental tohard segment ordering and cohesion. The migration of the func-tional groups to minimize the solid surface energy is facilitated bythe local segmental motion of polymers. Polar groups at theoutermost surface would increase the adhesiveness of the surfaceby increasing the surface energy whereas less polar groups woulddecrease the bondability of the surface. The polar component ofsurface tension gp

SV is higher for MDI-based polyurethane (P3) thanthe values determined for H12MDI-based polyurethanes (P1, P2),Table 5. The disperse component of surface tension, gdSV, of thepolyurethanes P1 and P3 with the same soft segment show closevalues but lower than that determined for P2 containing morehydrophilic PEG600 co-segment. The order found for surface-freeenergy (gSV) and free energy of adhesion (Wa) is as follows:P2 > P3 > P1.

Table 4Contact angle (q) degrees of different liquids and polyurethane samples.

Samplea Water Ethylene glycol CH2I2

P1 129 108 62P2 97 71 54P3 102 85 79

a Sample P4 does not possess adequate film properties.

Table 5Surface parameters for polyurethane samples.

Sample gpSV, mN/m gdSV, mN/m gSL, mN/m gSV, mN/m Wa, mN/m, water/EG DGw, mJ/m2 gdSV=gSV � 100, %

P1 0.046 10.38 50.07 10.43 27.02/32.83 �26.98 99.5P2 1.88 22.84 33.27 24.73 64.26/63.46 �63.92 92.3P3 3.48 10.93 29.69 14.41 57.52/51.9 �57.66 75.8

D. Filip et al. / Polymer Degradation and Stability 98 (2013) 951e957956

The results show that possibility to modulate the surfacestructure and properties by adjusting the chemical structure ofpolyurethane segments.

By calculation of free energy of hydration, DGw, thehydrophobeehydrophile balance of studied polyurethanes is eval-uated. The DGw values are obtained from Eq. (6), [43]:

DGw ¼ �gLVð1þ cos qwaterÞ (6)

where gLV is the total surface tension of water (72.8 mN/m) andqwater is contact angle of water with polyurethanes. The results arepresented in Table 5.

In the literature [43,44] it is stipulated that forDGw < �113 mJ m�2 the polymer can be considered more hydro-philic while when DGw > �113 mJ m�2 it should be consideredmore hydrophobic. All studied polyurethane samples are very hy-drophobic due to Pluronic L-61 soft segment. The order found forfree energy of hydration (DGw) is as follows: P2 < P3 < P1 whilethat found for interfacial tension (gSL) and the contribution of thedisperse component to the surface-free energy ðgd

SV=gSV � 100Þ isas follows: P1 > P2 > P3. The highest values of free energy of hy-dration and interfacial tension and the contribution of the dispersecomponent to the surface-free energy are for the most hydrophobicpolyurethane sample P1.

Free energy of hydration and interfacial tension are veryimportant in that they determine the interactional force betweentwo different media and control the dynamic of the molecular self-assembling, wettability of the surface, space distribution andadhesiveness.

4. Conclusions

New b-cyclodextrin-based side-chain azo amphiphilic poly-urethanes with different soft segment lengths have been synthe-sized. Thermal analysis results evidence the biphasic character ofsynthesized poly(ether urethanes) and Tgs corresponding to softsegment are found higher due to the rigidity introduced in thepolymer matrix by b-cyclodextrin. Evaluation of the thermal sta-bility of these poly(ether urethanes) evidences that b-cyclodextrinmoiety induces onset degradation temperatures higher than260 �C;MDI-based poly(ether urethanes) aremore thermally stablethan the hydrogenated MDI-based polyurethanes indicated byhigher values of onset degradation temperature values and higheractivation energy values of the former ones. Contact angle andsurface parameter values confirm the hydrophobic character ofpoly(ether urethanes) due to hydrophobic soft segment, Pluronic L-61. Poly(ether urethane) sample containing PEG600 co-segmentshows less hydrophobic properties.

Acknowledgement

The research leading to these results has received funding fromthe European Union’s Seventh Framework Programme (FP7/2007e2013) under grant agreement no. 264115 e STREAM.

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