Studies on the blends of polycarbonate and highly branched polystyrene

A highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of this highly branched polystyrene as a melt modifier for polycarbonate (PC) was attempted. Indeed, the results show that the addition of highly branched polystyrene can decrease the melt viscosity of PC with little change in mechanical properties, although the blends do exhibit lower thermal stability compared with pure PC. Extrapolation shows that all of the blends have an initial weight loss temperature above 450°C with a statistic heat‐resistant index T_s above 225°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2425–2430, 2004     

Evaluation of mechanical properties of polypropylene/polycarbonate/SEBS ternary polymer blends using Taguchi experimental analysis

In this work, ternary polymer blends based on polypropylene (PP)/polycarbonate (PC)/poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) (SEBS) triblock copolymer and a reactive maleic anhydride grafted SEBS (SEBS‐g‐MAH) at fixed compositions are prepared using twin‐screw extruder at different levels of die temperature (235‐245‐255°C), screw speed (70‐100‐130 rpm), and blending sequence (M1‐M2‐M3). In M₁ procedure, all of the components are dry blended and extruded simultaneously using Brabender twin‐screw extruder, whereas in M₂ procedure, PC, SEBS, and SEBS‐g‐MAH minor phases are first preblended in twin‐screw extruder and after granulating are added to PP continuous phase in twin‐screw extruder. Consequently, in M₃ procedure, PP and SEBS‐g‐MAH are first preblended and then are extruded with other components. The influence of these parameters as processing conditions on mechanical properties of PP/PC/SEBS ternary blends is investigated using L9 Taguchi experimental design. The responding variables are impact strength and tensile properties (Young's modulus and yield stress), which are influenced by the morphology of ternary blend, and the results are used to perform the analysis of mean effect as well. It is shown that the resulted morphology, tensile properties, and impact strength are influenced by extrusion variables. Additionally, the optimum processing conditions of ternary PP/PC/SEBS blends were achieved via Taguchi analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

PC/HBPS共混改性的研究

采用过渡金属催化原子转移自由基聚合反应的方法，合成了高支化聚苯乙烯(HBPS)；研究了聚碳酸酯(PC)／HBPS共混物的流动性能、力学性能、热性能及其相态结构。结果表明：在基体PC中加入质量分数不高于2％的HBPS后，共混物的熔体质量流动速率增加，流动性能明显改善，其冲击强度、拉伸强度、拉伸弹性模量和玻璃化转变温度等性能基本保持不变。     

A study on the effects of SEBS‐g‐MAH on the phase morphology and mechanical properties of polypropylene/polycarbonate/SEBS ternary polymer blends

In this work, five ternary blends based on 70% by weight (wt %) of polypropylene (PP) with 30% wt of polycarbonate (PC)/poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene)(SEBS) dispersed phase consists of 15 wt % PC and 15 wt % reactive (maleic anhydride grafted) and nonreactive SEBS mixtures at various ratios were prepared in a co‐rotating twin screw extruder. scanning electron microscopy (SEM) micrographs showed that the blends containing only nonreactive SEBS exhibited a fine dispersion of core‐shell particles. With decreasing the SEBS/SEBS‐g‐Maleic Anhydride (MAH) weight ratio, the morphology changed from the core‐shell particles to a mixed of core‐shell, rod‐like and individual particles. This variation in phase morphology affected the thermal and mechanical properties of the blends. DSC results showed that the blends containing only nonreactive SEBS exhibited a minimum in degree of crystallinity due to the homogeneous nucleation of core‐shell particles. Mechanical testing showed that in the SEBS/SEBS‐g‐MAH weight ratio of 50/50, the modulus and impact strength increased compared with the PP matrix while the yield stress had minimum difference with that of PP matrix. These effects could be attributed to the formation of those especial microstructures revealed by the SEM studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Formation of co‐continuous PLLA/PC blends with significantly improved physical properties by reactive comb polymers

A kind of reactive comb (RC) polymer, which is constituted by poly(methyl methacrylate) backbone and side chains and a few epoxide groups that distribute randomly along the backbone, has been applied as compatibilizers for the thermodynamically immiscible poly(l ‐lactide) (PLLA)/polycarbonate (PC) blend (50/50, wt/wt). Phase morphology and physical properties of the compatibilized PLLA/PC blends are characterized by scanning electron microscopy, transmission electron microscopy, and tensile tests. It has been found that the morphologies of the PLLA/PC blends are significantly ameliorated with the addition of RC polymers. A type of PLLA/PC blend with stable co‐continuous morphology has been achieved by the incorporation of more than 3 wt % of RC polymers. The mechanical tests showed that the co‐continuous PLLA/PC blends have an excellent stiffness‐toughness balance with high modulus and significantly improved ductility. Especially, the elongation at break of the PLLA/PC blend compatibilized by 10 wt % of RC polymers is 10 times higher than that of neat PLLA, in which the blend exhibits a cocontinuous lamellar microstructure. Furthermore, the PLLA/PC blends with cocontinuous morphology exhibit dramatically improved thermal stability as compared to neat PLLA when the temperature is over the T_g of the PLLA phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46047.     

Curing characteristics,morphology, thermal stability,mechanical properties,and irradiation resistance of methylethylsilicone/methylphenylsilicone rubber blends

Methylethylsilicone rubber (MESR)/methylphenylsilicone rubber (MPSR) blends were cured with 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy)hexane. The curing characteristics, morphology, thermal behaviors, mechanical properties at different temperatures, radiation resistance, and thermal aging resistance of the MESR/MPSR blends were investigated. The results show that a high MPSR content could decrease the optimum curing time and improve the scorch safety. Dynamic mechanical analysis revealed that the glass‐transition temperature of the blends increased slightly with the addition of MPSR. Scanning electron microscopy showed that MESR and MPSR had good compatibility in the blends. Thermogravimetric analysis indicated that the thermal stability of the blends increased with increasing quantity of MPSR. The blends had excellent mechanical properties at low temperatures. However, these properties were significantly reduced when the temperature was increased. Moreover, changes in the mechanical properties decreased with increasing MPSR content at high temperatures, especially at temperatures higher than 100°C. In addition, the radiation resistance and thermal aging resistance of the blends increased with increasing MPSR content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40529.     

Studies on morphology and thermomechanical performance of ABS/PC/organoclay hybrids

In the present research, poly(acrylonitrile‐butadiene‐styrene)/polycarbonate (ABS/PC) blends were prepared in a twin screw extruder. An attempt to reinforce and promote compatibility of the above systems was made by the incorporation of organically modified montmorillonite (OMMT, Cloisite 30B), as well as by the addition of compatibilizer (ABS grafted with maleic anhydride, ABS‐g‐MAH), and the effect of those treatments on the morphology, thermal transitions, rheological, and mechanical properties of the above blends was evaluated. The addition of compatibilizer in ABS/PC blends does not significantly affect the glass transition temperature (T_g) of SAN and PC phases, whereas the incorporation of Cloisite 30B decreases slightly the T_g values of SAN and, more significantly, that of PC in compatibilized and uncompatibilized blends. The T_g of PB phase remains almost unaffected in all the examined systems. The obtained results suggest partial dissolution of the polymeric components of the blend and, therefore, a modified Fox equation was used to assess the amount of PC dissolved in the SAN phase of ABS and vice versa.Reinforcing with OMMT enhances the miscibility of ABS and PC phases in ABS/PC blends and gives the best performance in terms of tensile strength, modulus of elasticity, and storage modulus, especially in 50/50 (w/w) ABS/PC blends. The addition of ABS‐g‐MAH compatibilizer, despite the improvement of intercalation process in organoclay/ABS/PC nanocomposites, did not seem to have any substantial effect on the mechanical properties of the examined blends. POLYM. COMPOS., 35:1395–1407, 2014. © 2013 Society of Plastics Engineers     

Blends of epoxy resins and polyphenylene oxide as processing aids and toughening agents 2: Curing kinetics,rheology, structure and properties

The curing behaviour, chemorheology, morphology and dynamic mechanical properties of epoxy ? polyphenylene oxide (PPO) blends were investigated over a wide range of compositions. Two bisphenol A based di‐epoxides ? pure and oligomeric DGEBA ? were used and their cure with primary, tertiary and quaternary amines was studied. 4,4′‐methylenebis(3‐chloro‐2,6‐diethylaniline) (MCDEA) showed high levels of cure and gave the highest exotherm peak temperature, and so was chosen for blending studies. Similarly pure DGEBA was selected for blending due to its slower reaction rate because of the absence of accelerating hydroxyl groups. For the PPO:DGEBA340/MCDEA system, the reaction rate was reduced with increasing PPO content due to a dilution effect but the heat of reaction were not significantly affected. The rheological behaviour during cure indicated that phase separation occurred prior to gelation, followed by vitrification. The times for phase separation, gelation and vitrification increased with higher PPO levels due to a reduction in the rate of polymerization. Dynamic mechanical thermal analysis of PPO:DGEBA340/MCDEA clearly showed two glass transitions due to the presence of phase separated regions where the lower T_g corresponded to an epoxy‐rich phase and the higher T_g represented the PPO‐rich phase. SEM observations of the cured PPO:DGEBA340/MCDEA blends revealed PPO particles in an epoxy matrix for blends with 10 wt% PPO, co‐continuous morphology for the blend with 30 wt% PPO and epoxy‐rich particles dispersed in a PPO‐rich matrix for 40wt% and more PPO. © 2014 Society of Chemical Industry     

Boiling water aging of polycarbonate and polycarbonate/acrylonitrile–butadiene–styrene resin and polycarbonate/low‐density polyester blends

The effects of boiling water on the mechanical and thermal properties and morphologies of polycarbonate (PC), PC/acrylonitrile–butadiene–styrene resin (PC/ABS), and PC/low‐density polyester (PC/LDPE) blends (compositions of PC/ABS and PC/LDPE blends were 80/20) were studied. PC and the PC/ABS blend had a transition from ductile to brittle materials after boiling water aging. The PC/LDPE blend was more resistant to boiling water aging than PC and the PC/ABS blend. The thermal properties of glass‐transition temperature (T_g) and melting temperature (T_m) in PC and the blends were measured by DSC. The T_g of PC and PC in the PC/ABS and PC/LDPE blends decreased after aging. The T_g of the ABS component in the PC/ABS blend did not change after aging. The supersaturated water in PC clustered around impurities or air bubbles leading to the formation of microcracks, which was the primary reason for the ductile–brittle transition in PC, and the microcracks could not recover after PC was treated at 160°C for 6 h. The PC/ABS blend showed slightly higher resistance to boiling water than did PC. The highest resistance to boiling water of the PC/LDPE blend may be attributed to its special structural morphology. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 589–595, 2003     

Mechanical properties,oil resistance,and thermal aging properties in chlorinated polyethylene/natural rubber blends

The use of natural rubber (NR) for partly substituting elastomeric chlorinated polyethylene (CPE) was determined. Mechanical and thermal aging properties as well as oil resistance of the blends were also investigated. The amount of NR in blends significantly affected the properties of the blends. The blends with NR content up to 50 wt % possessed similar tensile strength to that of pure CPE even after oil immersion or thermal aging. Modulus and hardness of the blends appeared to decrease progressively with increasing NR content. These properties also decreased in blends after thermal aging. After oil immersion, hardness decreased significantly for the blends with high NR content, whereas no change in modulus was observed. The dynamic mechanical properties were determined by dynamic mechanical thermal analysis. NR and CPE showed damping peaks at about ?40 and 4 °c, respectively; these values correlate with the glass‐transition temperatures (T_g) of NR and CPE, respectively. The shift in the T_g values was observed after blending, suggesting an interfacial interaction between the two phases probably caused by the co‐vulcanization in CPE/NR blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 22–28, 2002; DOI 10.1002/app.10171     

PC/HBPS共混物蠕变性能的研究

采用旋转流变仪研究了PC/HBPS共混物的蠕变性能。研究结果表明:共混物PC/HBPS较纯PC的蠕变性能得到了改善,且随着HBPS含量的增加,其改善效果越明显。     

Influences of the phenolic curative content and blend proportions on the properties of dynamically vulcanized natural rubber/acrylonitrile–butadiene–styrene blends

The vulcanization of natural rubber (NR)‐blended acrylonitrile–butadiene–styrene (ABS) was carried out with a phenolic curing agent by a melt‐mixing process. The NR compound was first prepared before blending with ABS. The effects of the phenolic curative contents (10, 15, and 20 phr) and blend proportions (NR/ABS ratio = 50 : 50, 60 : 40, and 70 : 30) on the mechanical, dynamic, thermal, and morphological properties of the vulcanized NR/ABS blends were investigated. The tensile strength and hardness of the blends increased with increasing ABS content, whereas the elongation at break decreased. The strength property resulting from the thermoplastic component and the vulcanized NR was an essential component for improving the elasticity of the blends. These blends showed a greater elastic response than the neat ABS. The thermal stability of the blends increased with increasing ABS component. Scanning electron micrographs of the blends showed a two‐phase morphology system. The vulcanized 60 : 40 NR/ABS blend with 15‐phr phenolic resin showed a uniform styrene‐co‐acrylonitrile phase dispersed in the vulcanized NR phase; it provided better dispersion between the NR and ABS phases, and this resulted in superior elastic properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42520.     

A comparative study on different rubbery modifiers: Effect on morphologies,mechanical, and thermal properties of PLA blends

To improve the impact toughness of poly(lactic acid) (PLA), four kinds of rubbery modifiers, including ground tyre rubber (GTR), styrene‐butadiene‐styrene block copolymer (SBS), ethylene‐α‐octene copolymer (EOC) and glycidyl methacrylate grafted EOC (mEOC), were introduced for fabricating the PLA blends. The morphological structures, mechanical properties, thermal stability and thermal decomposition kinetics of pristine PLA and the blends were investigated. Results showed that representative droplet‐matrix structures were observed in the PLA blends, of which the PLA/SBS blend presented the smallest domains while PLA/EOC case had the largest elastomeric particle size. Accordingly, the highest impact toughness and elongation at break were achieved by PLA/SBS blend, whereas the tensile strength and elastic modulus for the blends were all lower than that of pristine PLA. Though the incorporation of rubbery modifiers barely altered the peak temperature of melting, the degrees of crystallinity for blends were declined sharply. The results of thermo gravimetric analysis indicated thermal degradation process of PLA phase was accelerated by rubbery modifiers and evidenced by the relative higher mass conversion at peak temperature. The reaction order of PLA phase for blends calculated by Carrasco method exhibited similar values when compared with control sample. However, the values of activation energy were rather lower than that of pure PLA. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43340.     

Blends of bisphenol A polycarbonate and rubber‐toughened styrene–maleic anhydride copolymers

The morphology and mechanical properties of polycarbonate (PC) blends with rubber‐toughened styrene–maleic anhydride copolymer materials (TSMA) were investigated and compared with the properties of blends of PC with acrylonitrile–butadiene–styrene (ABS) materials. The PC/TSMA blends showed similar composition dependence of properties as the comparable PC/ABS blends. Polycarbonate blends with TSMA exhibited higher notched Izod impact toughness than pure PC under sharp‐notched conditions but the improvements are somewhat less than observed for similar blends with ABS. Since PC is known for its impact toughness except under sharp‐notched conditions, this represents a significant advantage of the rubber‐modified blends. PC blends with styrene–maleic anhydride copolymer (SMA) were compared to those with a styrene–acrylonitrile copolymer (SAN). The trends in blend morphology and mechanical properties were found to be qualitatively similar for the two types of copolymers. PC/SMA blends are nearly transparent or slightly pearlescent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1508–1515, 1999     

Fabrication of polypropylene blends with excellent low‐temperature toughness and balanced toughness‐rigidity by a combination of EPR and SEEPS

To overcome serious rigidity depression of rubber‐toughened plastics and fabricate a rigidity‐toughness balanced thermoplastic, a combination of styrene‐[ethylene‐(ethylene‐propylene)]‐styrene block copolymer (SEEPS) and ethylene‐propylene rubber (EPR) was used to toughen polypropylene. The dynamic mechanical properties, crystallization and melting behavior, and mechanical properties of polypropylene (PP)/EPR/SEEPS blends were studied in detail. The results show that the combination of SEEPS and EPR can achieve the tremendous improvement of low‐temperature toughness without significant strength and rigidity loss. Dynamic mechanical properties and phase morphology results demonstrate that there is a good interfacial strength and increased loss of compound rubber phase comprised of EPR component and EP domain of SEEPS. Compared with PP/EPR binary blends, although neither glass transition temperature (T_g) of the rubber phase nor T_g of PP matrix in PP/EPR/SEEPS blends decreases, the brittle‐tough transition temperature (T_bd) of PP/EPR/SEEPS blends decreases, indicating that the increased interfacial interaction between PP matrix and compound rubber phase is also an effective approach to decrease T_bd of the blends so as to improve low‐temperature toughness. The balance between rigidity and toughness of PP/EPR/SEEPS blends is ascribed to the synergistic effect of EPR and SEEPS on toughening PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45714.     

Preparation and properties of foamed cellulose acetate/polylactic acid blends

In order to improve the foaming performance of pure cellulose acetate (CA), blends were prepared by mixing polylactic acid (PLA) in CA and foamed by supercritical CO₂ (ScCO₂) in this study. The effect of PLA content (percentage by mass of blend) on structure, thermal properties, rheological properties, foaming properties and mechanical properties of the blends was investigated. The results showed that the addition of PLA destroyed the original hydrogen bonds of CA, while the blends had good crystallization properties. At the same time, compared with pure CA, the glass transition temperature (T_g) of the blends decreased, and the initial decomposition temperature (T₀) was reduced from 349.41°C (pure CA) to 334.68°C (CA/20%PLA). In addition, the rheological properties of the blends were improved, and the viscosity was reduced, which was obviously beneficial to foaming process. The pore size and density of the foamed blends both reached the maximum value at 20%PLA. The presence of PLA could degrade the mechanical properties of the blends. However, the overall drop (1.01 KJ/m²) of impact strength of the blends after foaming is much smaller than that before foaming (12.11 KJ/m²), indicating that the improvement of foaming performance was beneficial to improve its impact strength.     

Melt rheology and properties of compatibilized recycled poly(ethylene terephthalate)/(styrene‐ethylene‐ethylene‐propylene‐styrene) block copolymer blends

Blends of recycled poly(ethylene terephthalate) (R‐PET) and (styrene‐ethylene‐ethylene‐propylene‐styrene) block copolymer (SEEPS) compatibilized with (maleic anhydride)‐grafted‐styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MAH) were prepared by melt blending. The compatibilizing effects of SEBS‐g‐MAH were investigated systematically by study of the morphology, linear viscoelastic behavior, and thermal and mechanical properties of the blends. The results show that there is good agreement between the results obtained by rheological measurement and morphological analysis. The rheological test shows that the melt elasticity and melt strength of the blends increase with the addition of SEBS‐g‐MAH. The Cole‐Cole plots and van Gurp‐Palmen plots confirm the compatibilizing effect of SEBS‐g‐MAH. However, the Palierne model fails to predict the linear viscoelastic properties of the blends. The morphology observation shows that all blends exhibit a droplet‐matrix morphology. In addition, the SEEPS particle size in the (R‐PET)/SEEPS blends is significantly decreased and dispersed uniformly by the addition of SEBS‐g‐MAH. Differential scanning calorimeter analysis shows that the crystallization behavior of R‐PET is restricted by the incorporation of SEEPS, whereas the addition of SEBS‐g‐MAH improves the crystallization behavior of R‐PET compared with that of uncompatibilized (R‐PET)/SEEPS blends. The Charpy impact strength of the blends shows the highest value at SEBS‐g‐MAH content of 10%, which is about 210% higher than that of pure R‐PET. J. VINYL ADDIT. TECHNOL., 22:342–349, 2016. © 2014 Society of Plastics Engineers     

Blends of poly(vinyl chloride) with α‐methylstyrene‐acrylonitrile‐butadiene‐styrene copolymer: Thermal properties,mechanical properties,and morphology

Binary blends of poly(vinyl chloride) (PVC) with α‐methylstyrene‐acrylonitrile‐butadiene‐styrene copolymer (AMS‐ABS) were prepared via melt blending. A single glass transition temperature (T_g) was observed by differential scanning calorimetry, thus indicating that PVC is miscible with the α‐methylstyrene‐acrylonitrile‐styrene in AMS‐ABS. The results from attenuated total reflection Fourier transform infrared spectra indicated that specific strong interactions were not available in the blends. With increasing amounts of AMS‐ABS, both heat distortion temperature and thermal stability were increased considerably. With regard to mechanical properties, flexural and tensile properties decreased with increasing AMS‐ABS content. A synergism was observed in impact strength. The morphology of both impact‐fractured and tensile‐fractured surfaces, observed by scanning electron microscopy, correlated well with the mechanical properties. It is suggested that there was a transition of fracture mechanisms with the changing composition of the binary blends—from shear yielding for blends rich in PVC to cavitation for blends rich in AMS‐ABS. J. VINYL ADDIT. TECHNOL., 19:1–10, 2013. © 2013 Society of Plastics Engineers     

Light scattering materials with tunable optical properties by controlling refractive index of the dispersed phase

Traditionally, the morphologies of the dispersed phase in Polycarbonate (PC)/poly(styrene‐co‐acrylonitrile) (SAN) blends were strongly influenced if AN content in SAN changed significantly even under constant processing conditions. This would hinder the pure research intended to study the effect of the refractive index difference between the polymer host and the polymeric dispersed particles on the optical properties tough. Therefore, we respectively prepared different PC/SAN light diffusion sheets with four types of SAN containing different AN content ranging just from 20 to 25 wt %, a narrow range that sufficiently ensures the relatively stable morphology of different SAN in PC matrix. The results suggest that the refractive index of SAN increases with an decreasing AN content, thus narrowing the refractive index difference between PC and SAN and producing PC/SAN(70/30) light diffusion sheets with an increasing transmittance and decreasing haze. The interesting phenomenon is further analyzed using Mie scattering theory. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44156.     

Studies on morphology,mechanical, thermal,and rheological behavior of extrusion‐blended polypropylene and thermotropic liquid crystalline polymer

Polypropylene (PP) was melt‐blended in a single‐screw extruder with a thermotropic Vectra B‐950 liquid crystalline polymer (LCP) in different proportions. The mechanical properties of such blends were compared in respect of their Young's moduli, ultimate tensile strength (UTS), percent elongation at break, and toughness to those of pure PP. The thermal properties of these blends were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphology was studied by using a polarizing light microscope (PLM) and a scanning electron microscope (SEM) while the rheological aspects of the blends and the pure PP were studied by a Haake Rheowin equipment. Mechanical analysis (tensile properties) of the blends showed pronounced improvement in the moduli and the UTS of the PP matrix in the presence of 2–10% of LCP incorporation. TGA of all the blends showed an increase in the thermal stability for all the blends with respect to the matrix polymer PP, even at a temperature of 410°C, while PP itself undergoes drastic degradation at this temperature. DSC studies indicated an increase in the softening range of the blends over that of PP. Morphological studies showed limited mixing and elongated fibril formation by the dispersed LCP phase within the base matrix (PP) at the lower ranges of LCP incorporation while exhibiting a tendency to undergo gross phase separation at higher concentrations of LCP, which forms mostly agglomerated fibrils and large droplets. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 767–774, 2003