Study on nonlinear phase‐separation for PMMA/α‐MSAN blends by dynamic rheological and small angle light scattering measurements

The phase‐separation behavior of poly(methyl methacrylate)/poly(α‐methyl styrene‐co‐acrylonitrile) (PMMA/α‐MSAN) blends upon heating was studied through dynamic rheological measurements and time‐resolved small angle light scattering, as a function of temperatures and heating rates. The spinodal temperatures could be obtained by an examination of the anomalous critical viscoelastic properties in the vicinity of phase‐separation induced by the enhanced concentration fluctuation on the basis of the mean field theory. It is found that the dependence of the critical temperatures determined by dynamic rheological measurements and small angle light scattering on heating rates both deviates obviously from the linearity, even at the very low heating rates. Furthermore, the cloud‐point curves decrease gradually with the decrease of heating rates and present the trend of approaching T_gs of the blends. The nonlinear dependence is in consistence with that extracted from the isothermal phase‐separation behavior as reported in our previous paper. It is suggested that the equilibrium phase‐separation temperature could be hardly established by the linear extrapolating to zero in the plotting of cloud points versus heating rates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1547–1555, 2006     

Confirmation of universality of time–humidity superposition principle for various water‐absorbable polymers through dynamic viscoelastic measurements under controlled conditions of relative humidity and temperature

Dynamic viscoelastic measurements were made for storage (E′) and loss (E″) tensile moduli of water‐absorbable polymers such as nylon‐6, nylon‐66, poly(vinyl alcohol), ethylene–vinyl alcohol copolymers, and regenerated cellulose under the control of stepwise scanned relative humidity at constant temperature by changes in the strain frequency over a wide range. Smooth master curves of log(E′) and log(E″) plotted against log(frequency) were successfully obtained for all samples. The evaluated shift factors changed with the relative humidity and could be interpreted well on the basis of a concept of free volume in the amorphous region. The free volume was affected sensitively, depending on the heat‐treatment condition and the types of polymers used. For nylon‐66 film, the dynamic viscoelastic measurements were made at different humidities and temperatures, from which one smooth master curve was obtained. This experimental result is important in realizing the similar effect of relative humidity and temperature on the expansion of free volume of the amorphous phase: the shift factor change induced by the relative humidity change of about 30% was equivalent to the shift factor change induced by the temperature change of about 30 °C. That is, the time–humidity superposition principle and the time–temperature superposition principle were applicable as equivalent contributors to the mechanical property of water‐absorbable polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1638–1650, 2001     

Fracture of model polyurethane elastomeric networks

Fracture properties of model elastomeric networks of polyurethane have been investigated with a double‐edge notch geometry. The networks were synthesized from monodisperse end‐functionalized polypropylene glycol precursors and a trifunctional isocyanate. All reagents were carefully purified and nearly defect‐free ideal networks were prepared at a stoichiometry very close to the theoretical one. Three networks were prepared: an unentangled network of short chains (M_n = 4 kg mol^?1), an entangled network of longer chains (M_n = 8 kg mol^?1) and a bimodal network with 8 kg mol^?1 and 1 kg mol^?1 chains. The presence of entanglements was found to increase significantly the toughness of the rubber, in particular at room temperature, relative to the bimodal networks and to the short chains network. Fracture experiments were carried out at different strain rates and temperatures and showed for all three networks a marked decrease in fracture toughness with increasing temperature and decreasing strain rate which mirrored reasonably well the rate and temperature dependence of tan δ, the dissipative factor. However the proportionality factor between tan δ, and G_IC was very material dependent and the shift factors obtained for the master curves of the viscoelastic properties could not be used to build fracture energy master curves. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Analysis of viscoelastic behavior and dynamic mechanical relaxation of copolyester based layered silicate nanocomposites using Havriliak–Negami model

The solid‐state viscoelastic properties are examined for intercalated nanocomposites based on a copolyester and (2‐ethyl‐hexyl)dimethyl hydrogenated‐tallow ammonium montmorillonite. The nanocomposites are prepared via the direct melt intercalation technique using a conventional twin‐screw extruder. Dynamic mechanical thermal analysis of the nanocomposites is conducted using two different test setups. The dynamic mechanical relaxation spectra show an increase in the storage modulus of the nanocomposite over the entire temperature range under study as compared to the pristine polymer (except in the transition region from 70 to 80 °C). These results are analyzed using the empirical Havriliak–Negami (HN) equation. The four temperature independent HN parameters (α, β, E₀, and E_∞) and one temperature dependent parameter (τ, the relaxation time) are determined by solving the HN equation for each temperature over the range of temperatures. The calculated moduli results fit well with the experimental values of the relaxation spectra for the nanocomposites. This study shows that the HN model can be applied to polymer layered silicate nanocomposites, and it can be used to predict their dynamic mechanical properties over a wide range of temperatures and frequencies a priori. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2657–2666, 2004     

Crystal structure and morphology of phenyl‐capped tetraaniline in the leucoemeraldine oxidation state

A series of crystals of phenyl‐capped tetraaniline in the leucoemeraldine oxidation state were obtained at different isothermal temperatures and were observed directly under transmission electron microscope. The crystals obtained at higher temperatures exhibit more perfect structures than those obtained at lower temperatures. Both the lamella thickness and the crystal size increase with crystallization temperature. The tetraaniline is apt to form larger scale crystals under lower degree of supercooling. However, their crystal structures keep steady with the crystallization temperature. The tetramer was found to adopt a monoclinic lattice with unit cell parameter of a = 13.93 Å, b = 8.82 Å, c = 23.20 Å, and β = 95.03°, as determined using electron diffraction tilting method combined with wide‐angle X‐ray diffraction experiment. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 764–769, 2006     

Temperature and aging dependence of strain‐induced crystallization and cavitation in highly crosslinked and filled natural rubber

We have investigated the structural changes occurring in highly crosslinked and carbon‐black filled natural rubber under uniaxial extension by small‐ and wide‐angle X‐ray scattering using synchrotron radiation. The experiments focused on strain‐induced crystallization (SIC) and nanocavitation and were carried out on a model series of materials as a function of temperature and aging conditions. We find that for all materials both SIC and cavitation decrease markedly with temperature and aging. However, the presence of carbon black filler shifts the ceiling temperature where SIC is observed to at least 120°C, presumably by a nucleating effect, maintaining the high strength of the elastomers. Interestingly, although in pure elastomers, the cavitation strength decreases with temperature, we find that in these filled elastomers the critical stress for the onset of cavitation increases significantly with temperature strongly suggesting that cavitation is due to the local confinement between fillers and supporting the idea of a glassy layer near the filler. Aging for 10 days at 110°C in oxygen‐free conditions decreases both SIC and cavitation and reduces the strength of the elastomer at high temperature. This is attributed to the formation of sulfur side chains hindering the crystallization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 780–793     

Effect of a post‐annealing process on microstructure and mechanical properties of high‐density polyethylene/silica nanocomposites

High‐density polyethylene (HDPE) and nanosilica nanocomposites were prepared for SiO₂ content up to 15 wt%. Microstructural characterization evidenced a homogenous distribution of silica aggregates with a mean size increasing with the filler content finally resulting in a rheological percolation between 7.5 and 10 wt%. Nanoparticles did not induce any significant impact on the matrix crystallinity but led to a real improvement on elastic properties accompanied with a large embrittlement above the percolation threshold. The effect of annealing near HDPE melting temperature was studied. Differential scanning calorimetry, X‐ray diffraction, and small‐angle X‐ray scattering analyses showed a significant change in the HDPE microstructure after annealing at 125°C. A large increase in the crystallinity (from 68 to 76%) and a clear improvement of Young's modulus (by 55%) were observed prior to polymer degradation. A valuable impact of silica particles on thermal stability was also obvious regarding the evolution of elastic properties for extended exposure times (850–1,200 h). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 535–546     

Viscoelastic properties of nanostructured natural rubber/polystyrene interpenetrating polymer networks

The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (T_g's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the T_g values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003     

Differences in self‐assembly features of thermoresponsive anionic triblock copolymers synthesized via one‐pot or two‐pot by atom transfer radical polymerization

The self‐assembly process in aqueous solutions of the methoxyl‐poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic sodium)‐block‐poly(N‐isopropyl acrylamide) (PNIPAAM) triblock copolymer, synthesized via two different atomic transfer radical polymerization methods, namely “one‐pot” (P3‐sample) and “two‐pot” (P2‐sample), was studied by various experimental techniques. The “one‐pot” procedure leads to a copolymer (P3) where the PNIPAAM block is contaminated with a minor quantity of 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (AMPS) residuals and this sample does not form micelles over the considered temperature region, but unimers and temperature‐induced aggregates coexist in the presence of a small amount of salt. The P2 polymer forms micelles and intermicellar structures, but the former moieties disappear at high temperatures, whereas the latter species contract with increasing temperature. Small‐angle neutron scattering results revealed correlation peaks, both for P3 and P2, and no micelle formation for P3, but a pronounced upturn of the scattered intensity at low wavevector values at elevated temperatures for the P2 copolymer. The findings from this study clearly show that the spurious AMPS residuals have a drastic influence on the self‐assembly and micelle formation of the triblock copolymer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 524–534     

Prediction of viscoelastic properties with coarse‐grained molecular dynamics and experimental validation for a benchmark polyurea system

To explore the relationship between microscopic structure and viscoelastic properties of polyurea, a coarse‐grained (CG) model is developed by a structure matching method and validated against experiments conducted on a controlled, benchmark material. Using the Green‐Kubo method, the relaxation function is computed from the autocorrelation of the stress tensor, sampled over equilibrium MD simulations, and mapped to a real time scale established by matching self‐diffusion rates of atomistic and CG models. Master curves computed from the predicted stress relaxation function are then compared with dynamic mechanical analysis experiments mapped to a wide frequency range by time–temperature superposition, as well as measurements of ultrasonic shear wave propagation. Computational simulations from monodisperse and polydisperse configurations, representative of the benchmark polyurea, show excellent agreement with the experimental measurements over a multidecade range of loading frequency. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 797–810     

Thermo‐/moisture‐responsive shape‐memory effect of poly(2‐ethyl‐2‐oxazoline) networks

In this work, poly(2‐ethyl‐2‐oxazoline) (PEtOx) is crosslinked to realize a moisture‐ and thermo‐responsive shape‐memory polymer. The obtained PEtOx networks exhibit excellent shape‐memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape‐memory cycles. The trigger temperature (T_trig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1053–1061     

Viscoelastic behavior of epoxy prepolymer/organophilic montmorillonite dispersions

Dispersions of a bisphenol A‐based epoxy resin with an organophilic montmorillonite (Nanofil 919) were studied by X‐ray diffraction and oscillatory shear rheometry. X‐ray studies reveal that the clay is intercalated by the epoxy and forms stable dispersions. The viscoelastic behavior of the nanodispersions was measured as a function of the Nanofil concentration and temperature. An increase in both G′ and G″ moduli was detected as the concentration increases. Furthermore, a transition from a liquid‐like behavior, at low temperatures, to a solid‐like behavior, at higher temperatures, was observed for all the samples. This transition is accounted for the formation of a percolated structure of interconnected tactoids through hydrophobic interactions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1837–1844, 2008     

Low‐temperature route to thermoplastic polyamide elastomers

Thermoplastic polyamide elastomers were obtained by polymerization of aminobenzoyl‐substituted telechelics derived from poly(tetrahydrofuran)‐diols (number‐average molecular weight: 1400 or 2000 g mol^?1) with several diacid dichlorides (terephthaloyl dichloride, 4,4′‐biphenyldicarbonyl dichloride, or 2,6‐naphthalenedicarbonyl dichloride) and chlorotrimethylsilane in N,N‐dimethylacetamide at 0–20 °C. The as‐prepared polymers had melting temperatures above 190 °C and exhibited elastic properties at room temperature, as evidenced by dynamic mechanical analysis and stress–strain measurements. The polymer with 2,6‐naphthalenedicarboxamide hard segments had the widest rubbery plateau within the series, the highest extension at break, and good recovery properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1449–1460, 2004     

Viscoelasticity of nanobubble‐inflated ultrathin polymer films: Justification by the coupling model

The nanobubble inflation method is the only experimental technique that can measure the viscoelastic creep compliance of unsupported ultrathin films of polymers over the glass–rubber transition zone as well as the dependence of the glass transition temperature (T_g) on film thickness. Sizeable reduction of T_g was observed in polystyrene (PS) and bisphenol A polycarbonate by the shift of the creep compliance to shorter times. The dependence of T_g on film thickness is consistent with the published data of free‐standing PS ultrathin films. However, accompanying the shift of the compliance to shorter times, a decrease in the rubbery plateau compliance is observed. The decrease becomes more dramatic in thinner films and at lower temperatures. This anomalous viscoelastic behavior was also observed in poly(vinyl acetate) and poly (n‐butyl methacrylate), but with large variation in the change of either the T_g or the plateau compliance. By now, well established in bulk polymers is the presence of three different viscoelastic mechanisms in the glass–rubber transition zone, namely, the Rouse modes, the sub‐Rouse modes, and the segmental α‐relaxation. Based on the thermorheological complexity of the three mechanisms, the viscoelastic anomaly observed in ultrathin polymer films and its dependence on chemical structure are explained in the framework of the Coupling Model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

The effect of light penetration depth on the LCST phase behavior of a thermo‐ and photoresponsive statistical copolymer in an ionic liquid

A reflection cloud point technique allows for rapid screening of light‐dependent phase separation temperatures of thermo‐ and photoresponsive polymer/ionic liquid solutions as a function of sample thickness, molecular weight, and copolymer composition. We systematically investigate the lower critical solution temperature (LCST) phase behavior of poly(benzyl methacrylate‐stat‐(4‐phenylazophenyl methacrylate)). Under UV light, the photoresponsive azobenzene‐based repeat unit becomes more polar as the cis form dominates, increasing its solubility in the ionic liquids 1‐ethyl‐3‐methyl imidazolium and 1‐butyl‐3‐methyl imidazolium bis(trifluoromethanesulfonyl)imide. This light‐dependent polarity change leads to two phase separation temperatures, depending on the illumination wavelength. Under visible light, which drives the azobenzene moiety into the trans ground state, the LCST shows no sample thickness dependence. Under UV light, however, sample thickness plays a significant role. Samples of around 1 mm thickness show no apparent difference under UV and visible light, whereas thinner samples show an increasing difference between the phase separation temperatures with decreasing sample thickness. Neither phase separation temperature exhibits a significant dependence on molecular weight. Increasing the photoresponsive monomer content did not lead to an increase in the difference between the phase separation temperatures at fixed thickness, due to a concomitant increase in UV light absorbed at the sample surface. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 281–287     

Influence of moisture on the viscoelastic relaxations in long aliphatic chain contained semiaromatic polyamide, (PA9‐T) fiber

The effect of moisture on the mechanical relaxation processes of semiaromatic semicrystalline polyamides synthesized by a long‐chain aliphatic diamine and terephthalic acid was investigated by dynamic viscoelastic analysis (DVA) and differential scanning calorimetry (DSC). Moreover, the implication of moisture with the amorphous and crystalline domains was also examined by temperature‐dependent wide‐angle X‐ray diffraction and Fourier transform infrared spectra. The characteristics of the relaxations such as α, β, γ, and the pronounced peak shoulder appeared at 25–100 °C in DVA tan δ curves were found to be strongly susceptible to the presence of moisture. With moisture evaporation, the peak shoulder of 25–100 °C and the β‐relaxation disappeared. The former is anticipated to originate from to the side group motion of hydrogen‐bonded water, whereas the later one is from the motions of the amide–water complex units. With the disappearance of the β‐relaxation, the γ‐relaxation appeared simultaneously in much lower temperatures and ultimately coupled with the δ‐relaxation. The γ‐relaxation is attributed to be associated with the molecular motion of the amide group and δ‐relaxation with for the motion of the methylene units. The existence of two types of water was identified in the polymer, namely, tightly bound and loosely bound. The tightly bound water is believed to be directly connected by hydrogen bonding with the strong polar groups and the loosely bound water weakly links with those connected water making hydrogen bridges. The moisture acts as a plasticizer in the polymer matrix, which causes quite a large depression in its glass transition temperature (T_g). WAXD and FTIR studies corroborated the existence of water solely in amorphous regions, i.e., no rapport of water with the crystalline parts. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2878–2891, 2003     

Novel silver‐loaded semi‐interpenetrating polymer network gel films with antibacterial activity

Novel semi‐interpenetrating polymer networks (SIPNs) based on segmented polyurethane‐urea and poly(N‐isopropylacrylamide‐co‐acrylic acid‐co‐butylmethacrylate) (poly(NIPAM‐co‐AA‐BMA)) were synthesized for the fabrication of silver nanoparticles (AgNPs) in the SIPN system that could be useful for wound dressing applications. The obtained SIPN films, after neutralization, showed high swelling in aqueous environments and good mechanical properties in both dry and hydrated states. Analysis of the dried SIPN films by differential scanning calorimetry and dynamic viscoelastic measurements revealed the presence of crosslinked copolymers as well as homopolymers in the SIPN system. The neutralized swollen SIPN film coordinated with the silver ions (Ag⁺) that were incorporated into it. AgNPs were subsequently formed by the reduction of Ag⁺. The formation of AgNPs was characterized by UV‐visible spectroscopy, atomic force microscopy, wide‐angle X‐ray diffraction, and thermogravimetric analysis (TGA). Bactericidal activity tests revealed a distinct zone of microbial inhibition within and around the silver‐doped SIPN films. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4950–4962, 2009     

Charge‐Functionalized and Structurally Enhanced (Cryo)Hybrids from Acrylic (Co)Monomers and Kaolin: Altering Physicochemical Properties via Cryotropic Gelation

The potential to improve mechanical, structural, and mechanochemical properties of charge‐functionalized poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA)‐based hybrid cryogels is investigated. The simple and versatile synthesis of hybrid cryogels with high strength and toughness using cationic DMAEMA and ionic comonomer 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid has been proposed via in situ free‐radical crosslinking (cryo)polymerization by which the properties of virgin polymer can be modulated to required applications by incorporation of inorganic filler kaolin (KLN). Two factors affecting swelling and elasticity of hybrid gels (referred as PDA/KLNm), KLN content and gel preparation temperature, are studied. The optimum KLN concentration for desired swelling and modulus of elasticity is determined as 0.80% (w/v). Effective crosslinking density of hybrid hydrogels increases with KLN addition and this dependence is expressed by a quadratic polynomial as a function of KLN concentration. The results show that obtained hybrid gels with multiresponsive properties could be regarded as “smart materials” in sensing and actuation applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1758–1778     

Interpenetrating thermophobic and thermophilic dual responsive networks

Poly(N‐acryloyl glycinamide) (PNAGA)/poly(N‐isopropyl acrylamide) (PNIPAAm) interpenetrating network (IPN) hydrogels were made by UV‐light initiated radical polymerization in two‐steps. The IPN hydrogels showed a double thermoresponsive behavior due to the combination of PNIPAAm (thermophobic) and PNAGA (thermophilic) networks. Increasing the content of the thermophobic PNIPAAm network leads to a change from a broad thermophilic volume phase transition temperature of PNAGA to a thermophilic–thermophobic‐type dual transition for the prepared IPN. Due to the double thermoresponsive character of the IPN gels, the mechanical properties are dependent upon temperature as demonstrated by performing tensile tests in water at 15 and 50 °C. Furthermore, the IPN hydrogels were characterized using turbidity measurements, SEM, and the determination of the equilibrium swelling ratio. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 539–544     

Influence of molecular architecture of S–S/B–S triblock copolymers on rheological properties

The influence of middle and outer block composition of symmetric triblock copolymers consisting of a polystyrene–polybutadiene (S/B) random middle block and two polystyrene (PS) outer blocks on morphology and rheological behavior has been investigated. Master curves are obtained by shifting the experimental data measured at different temperatures using time‐temperature superposition principle, the validity of which was confirmed in the linear viscoelastic regime. The rheological properties are observed to be strongly influenced by the relative composition of the S‐SB‐S triblock copolymers. Increasing the S/B ratio from 1:1 to 1:2 in the middle block has lead to a change in morphology from wormlike to lamellar, which is also accompanied with broad and sharp tan δ peaks in the dynamic mechanical measurements, respectively. The storage and loss modulus have been observed to increase with the increase in PS contents in the outer blocks and PB content in the middle block. The triblock copolymer with wormlike structure showed terminal linear viscoelastic behavior, whereas the ones with lamellar morphology showed nonterminal flow behavior in the similar low‐frequency regime. The relaxation modulus (G_t) has been observed to increase four times when the S/B ratio is increased from 1:1 to 1:2, whereas it increases threefold when the PS‐content in the outer block was increased by just 8 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2776–2788, 2006