Effects on the structure and properties of membranes formed by blending polydimethylsiloxane polyurethane into different soft‐segment waterborne polyurethanes

Polydimethylsiloxane polyurethane (PDMS‐PU), which was synthesized from PDMS as the soft segment, was blended into a variety of ester‐ or ether‐based soft‐segment waterborne polyurethanes with different concentrations to investigate the crystallization, thermal, and physical properties of the membrane formations. According to X‐ray analysis, the ether‐based PUs, synthesized from soft segments of poly(propylene glycol) (PPG1000) or poly(ethylene glycol) (PEG2000), were found to have maximum crystallinity at a 5% blending ratio of PDMS‐PU, but the ester‐based PU, synthesized from soft segments of polycaprolactone (PCL1250), had decreased crystallinity at a 5% blending ratio. Differential scanning calorimetric analysis revealed that the T_g,s values of PUs were highest when the blending ratio of PDMS‐PU was 5%–10%, except for PU from PCL1250. Moreover, ether‐based PUs showed maximum T_m,h values, but the T_m,h of the ester‐based PU was greatly reduced when PU with PCL1250 was blended with PDMS‐PU. In addition, the PU from PEG2000 had the highest melting entropy. Mechanical property analysis showed that the stress of ether‐based PUs would be increased when PUs were blended with a small amount of PDMS‐PU and that the stress of PU from poly(tetramethylene glycol) (PTMG1000) increased to its greatest value (20–30 MPa). On the other hand, the ester‐based PU, from PCL1250 blended with PDMS‐PU, would have reduced stress. On the whole, the stress and strain of PU from PEG1000 had excellent balance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 210–221, 2006     

The temperature-sensitive water vapor permeation control of polyurethane membrane using the graft-polymerized poly(N-isopropylacrylamide) and the impact on the tensile strength and shape recovery effect

Poly(N-isopropylacrylamide) (poly(NIPAM)) was grafted onto polyurethane (PU) using a graft-polymerization method to develop a thermo-responsive PU and to investigate the impact on cross-link density, solution viscosity, soft segment thermal transitions, tensile properties, shape memory effect, and water vapor permeation through PU membrane. The soft segment crystallization peak sharply decreased with the increase in NIPAM content, whereas the glass transition temperature (T_g) slightly increased with the increase of NIPAM content. The breaking tensile stress rapidly increased with the increase in NIPAM content due to the cross-linking effect between the grafted poly(NIPAM) chains, whereas the strain at break did not significantly decreased as the NIPAM content increased. The shape recovery at 10°C rapidly increased from 46.9% for plain PU to above 90% after the grafting of poly(NIPAM) onto PU, and the shape retention at ?25°C slightly decreased with the increase in NIPAM content. Finally, the grafting of poly(NIPAM) onto PU demonstrated the temperature-responsive control of water vapor permeation through PU film due to the conformational change of the grafted poly(NIPAM) with the increase of temperature and the potential applications of the resulting PUs are discussed.     

Application of recycled polyol and benzimidazole to the enhancement of antifungal activity of polyurethane

Recycled polyol and benzimidazole were both grafted onto polyurethane (PU) to enhance the surface hydrophilicity and antifungal activity, respectively. The two grafted groups affected the viscosity, crosslink density, soft segment glass transition, breaking stress, flexibility at freezing temperature, shape recovery at ?10 °C, surface hydrophilicity, and antifungal activity. The glass transition temperature increased from ?67.5 °C for plain PU up to ?60.8 °C after the grafting of polyol. The breaking stress and shape recovery of the grafted PU increased up to 425% and 200%, respectively, relative to plain PU because of the chemical linking by the grafted polyol. The hydrophilicity of PU, evaluated by the water contact angle and water swelling ratio, increased with increasing polyol content. A PU sample demonstrated excellent low‐temperature flexibility in comparison to plain PU and control sample. Finally, the PUs modified with grafted polyol and benzimidazole completely suppressed fungal growth. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46600.     

Thermal induced shape‐memory and self‐healing of segmented polyurethane containing diselenide bonds

Herein, we synthesized a series of polyurethane copolymers (PUs) with poly(1,4‐butylene adipate) glycol as soft segment and 2,4‐toluene diisocyanate as well as extenders including 1,4‐butanediol and di(1‐hydroxyethylene) diselenide as hard segment. The chemical structure, thermal property, crystallization behavior, shape memory, and self‐healing performances of the PUs were systematically characterized by a series of experiments. It was found that the PU2 containing a higher diselenide component (～33 mol %) exhibited both shape memory and self‐healing behaviors under a moderate temperature (～57 °C). Meanwhile, the PUs showed a good repeatability of shape memory function, and their fixity and recovery ratios were all above 90%. Additionally, the dynamic exchangeable feature of diselenide bonding endues the PUs chains with an acceptable reprocessability and self‐healing performances, and the PU2 sample could be healed for five times by thermal treatment with the healing efficiencies above 70%. This work provides a heuristic perspective for the development of shape memory and self‐healing materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46326.     

Morphology and water vapor permeability of temperature‐sensitive polyurethanes

A series of segmented polyurethanes (PUs) were prepared, in which five different polyols and hexamethylene diisocyanate were used as soft segments, and 4,4′‐diphenylmethane diisocyanate, hydrophilic segment poly (ethylene glycol) 200 (PEG 200), and chain extender 1,4‐butanediol were used as hard segment. Morphology of the PUs was investigated using differential scanning calorimetry, wide angle X‐ray diffraction, polarizing microscopy, and transmission electron microscopy. Water vapor permeability of the membranes as a function of temperature was tested accordingly. Results show that the presence of PEG200 interferes the crystallization of hard segment in these PUs, and at the same time, increases phase compatibility between soft and hard segment in the PET‐PU. It leads to a lower crystal melting temperature and degree of crystallinity of soft segment in the segmented PU than those of pure polyols, and no crystallization existing in hard segment. A morphological model is proposed, that is, aggregated soft‐segment‐rich domains can be observed clearly in the PUs with high crystallinity in soft segment, while identifiable hard domains are well‐distributed in the soft segment domains in the PU with low crystallinity. Within the temperature range of crystal melting, water vapor permeability of the PU membranes increases significantly with increase of temperature. Such temperature‐sensitive property is triggered by crystal melting of soft segment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Diffusion and sorption of benzene vapor through polybutadiene‐, polybutadiene/styrene‐, and polybutadiene/acrylonitrile‐based polyurethanes

A series of polyurethane (PU) films made from toluene diisocyanate (TDI), 1,4‐butanediol (BDO), and hydroxyl‐terminated polybutadiene (HTPB), hydroxyl terminated polybutadiene/styrene (HTBS), or hydroxyl terminated polybutadiene/acrylonitrile (HTBN) was synthesized by solution polymerization. The absorption of benzene vapor was found mainly in the soft phase. The equilibrium adsorption (M_∞) was reduced with increasing hard segment content for all the PUs. The values of M_∞ were in the sequence of HTBN‐PUs > HTBS‐PUs > HTPB‐PUs, which could be explained by the different interaction parameters between soft segments and benzene. The HTBN‐PU film showed the lowest degree of phase segregation and had more hard segments intermixed in the soft phase, restricting the movement of soft segments, and therefore resulted to non‐Fickian behavior, while the HTPB‐PU is antithetical. FTIR and atomic force microscopy were utilized to identify the hydrogen bonding behavior and morphology change of the PU films before and after the absorption of benzene vapor. The tensile strength of the HTBN‐PUs showed a greater decrease than that of HTBS‐PUs and HTPB‐PUs after absorbing benzene vapor. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2984–2991, 2004     

Thermoplastic polyurethanes with controlled morphology based on methylenediphenyldiisocyanate/isosorbide/butanediol hard segments

Isosorbide, a cyclic, rigid and renewable diol, was used as a chain extender in two series of thermoplastic polyurethanes (PUs). Isosorbide was used alone or in combination with butanediol to examine the effects on the morphology of PU. Two series of materials were prepared – one with dispersed hard domains in a matrix of polytetramethylene ether glycol soft segments of molecular weight 1400 g mol^?1 (at 70 wt% soft segment concentration, SSC) and the other with co‐continuous soft and hard phases at 50 wt% SSC. We investigated the detailed morphology of these materials with optical and atomic force microscopy, as well as ultra‐small‐angle X‐ray scattering. The atomic force microscopy measurements confirmed the different morphologies in PUs with 50 wt% SSC and with 70 wt% SSC. Small‐angle X‐ray scattering data showed that in PU with 70 wt% SSC, the hard domain size varied between 2.4 and 2.9 nm, and decreased with increasing isosorbide content. In PU with 70 wt% SSC, we found that the correlation length and average repeat distances became smaller with increasing isosorbide content. We estimated the thickness of the diffuse phase boundary for PU with 70 wt% SSC to be ca 0.5 nm, decreasing slightly with increasing isosorbide content. © 2015 Society of Chemical Industry     

Effect of microphase‐separation promoters on the shape‐memory behavior of polyurethane

A series of segmented polyurethanes (PUs) with novel thermosensitive shape‐memory behavior were synthesized via the in situ addition of a small amount of 1‐octadecanol (ODO) to a PU system. For comparison, liquid paraffin (LP) modified PUs were also synthesized. The effects of a small amount of ODO or LP on the PU suprastructure and the thermosensitive shape‐memory properties were studied with X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape‐memory studies. The results indicated that the in situ addition of a small amount of ODO (e.g., 0.3 wt %) remarkably promoted microphase separation, facilitating the ordered packing of soft segments and the formation of perfect hard‐segment domains and thus significantly improving the shape‐memory properties. In contrast, LP had less significant influence on the shape‐memory behavior because of the macrophase separation of these nonpolar alkyl chains from the PU system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5224–5231, 2006     

Effects of the structures of end groups of pendant polydimethylsiloxane attached to a polyurethane copolymer on the low temperature toughness

End groups with different structures were grafted to polyurethane (PU) using poly(dimethylsiloxane) (PDMS) as a spacer. The low‐temperature toughness of the PUs was tested at ?30°C, and the structure selectivities of the end groups for low‐temperature toughness were compared. The PDMS functioned as a flexible linker that connected the end groups to the PUs. The tensile strength of the PU generally improved despite the grafting of PDMS and end groups. The conventional shape recovery ratio at 45°C remained greater than 90%, regardless of the content and structure of PDMS and the end group. The PU that contained an adamantyl group (cubic) or a naphthyl group (planar rectangle) showed instant recovery, even at ?30°C, but the PU that contained a phenyl (planar square) or phenoxyphenyl (bent squares) group required warming to 0°C for a similar degree of recovery but showed improvement over a linear PU without any end group. The characteristic structure of the end group was responsible for the selective low‐temperature toughness. The low‐temperature toughness results and the thermal and mechanical properties of the PUs are discussed. POLYM. ENG. SCI., 55:1931–1940, 2015. © 2014 Society of Plastics Engineers     

Microstructure and properties of poly(urethane-siloxane)s based on hyperbranched polyester of the fourth pseudo generation

Poly(urethane-siloxane) networks based on hydroxyethoxy propyl terminated poly(dimethylsiloxane) (PDMS) as the soft segment and 4,4′-methylenediphenyl diisocyanate (MDI) and two hyperbranched polyesters with different core as the hard segments were characterized by swelling experiments, thermal analyses (DSC and TG), thermomechanical analysis (DMTA), X-ray scattering studies, SEM and AFM analyses, water contact angle and water absorption measurements, as well as surface free energy determination. From these studies, structure–property relationships were elucidated. Hyperbranched polyesters based on 2,2-bis(hydroxymethyl)propionic acid and ethoxylated pentaerythritol or di-trimethylolpropane as core (BH-40 and HBP-4) were used as crosslinkers for the samples of different series. Both series are composed of samples having different PDMS (i.e., soft segment) content. The crosslinking density and extent of hydrogen bonding showed an influence on the polyurethane (PU) properties. It was found that higher crosslinking density and better thermal stability of PUs based on BH-40 compared to HBP-4 based PUs are due to the less dense structure of BH-40. DMTA experiments revealed that the networks exhibit two glass transition temperatures, of the soft and hard segments, and one secondary relaxation process. The crosslinking density and extent of the microphase separation increased and thermomechanical properties were improved with decreasing content of PDMS. With increasing PDMS content, the surface of the polyurethane networks became more hydrophobic, the surface free energy decreased and thermal stability was improved. The obtained results revealed that synthesized PUs have good thermal and thermomechanical properties, which can be tailored for the potential use in the coating technology by changing the type of hyperbranched polyester or PDMS content.     

Study on the influence of thermal characteristics of hyperbranched polyurethane phase change materials for energy storage

A series of hyperbranched polyurethane (HB‐PU) phase change induced energy storage materials were prepared by polyethylene glycol (PEG), methylene diphenyl 4,4′‐diisocyanate (MDI), and hyperbranched polyester polyalcohol via a two‐step process. The influence of thermal characteristics of HB‐PU was investigated using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). It has been found that the thermal characteristics of HB‐PU are affected by some factors. Such as the molecular weight and content of soft segment, once the M_n of PEG soft segments is larger than the critical M_n (2000 g/mol), both the phase change enthalpy and temperature increase as M_n of PEG soft segment and soft segment content (SSC) increase. The influence of the microstructure of hard segment originates from diisocyanate and hyperbranched polyester polyalcohol, HB‐PUs with regular microstructure and lower generation of hyperbranched polyester polyalcohol have high energy storage capability. Furthermore, the conditions of measurement affect the thermal characteristics of materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Shape memory segmented polyurethanes: dependence of behavior on nanocellulose addition and testing conditions

The response of synthesized shape memory segmented polyurethanes (PUs) was affected by the addition of cellulose nanocrystals, as well as by the various conditions selected to carry out thermomechanical cyclic tests. The PUs were synthesized from an α‐hydro‐ω‐hydroxy‐poly(ethylene oxide), tolylene‐2,4‐diisocyanate and 1,4‐butanediol as chain extender. Nanocomposites were prepared by mixing a suspension of cellulose nanocrystals in N,N‐dimethylformamide with the thermoplastic PU dissolved in the same organic solvent. The thermal properties of the neat PU and resulting composites were examined using differential scanning calorimetry. It was found that cellulose addition increases the PU soft segment melting and crystallization temperatures and the degree of crystallinity of this phase. Shape memory behavior was studied using cyclic thermal tensile tests. Both neat PU and composites exhibit shape memory properties, with fixity and recovery values that depend on heating temperature, imposed deformation, deformation rate and nanofiller addition. Copyright © 2011 Society of Chemical Industry     

Block architecture influence on the structure and mechanical performance of drawn polyurethane elastomers

Some natural biopolymers such as spider silk exhibit superb mechanical properties, characterised by their great toughness. Synthetic polyurethane (PU) copolymers also endow great toughness but lack silk's stiffness and strength. The aim of this work was to elucidate the role of segment block architectural features that influence PU stiffness and strength after cold drawing. For this purpose PUs with varied soft segment character, crystalline versus rubbery, as well as with different hard segment chemistries, 4,4′‐diphenylmethane diisocyanate/1,4‐butanediol versus 1,6‐hexamethylene diisocyanate/1,4‐butanediol, were synthesised by a two‐step polymerisation method. We found that the architecture of both block segments has a dramatic influence on drawn PU mechanical performance, in which PUs with crystallisable soft segments and crystalline hard segments are shown to have a greater impact on developing stiffer and stronger materials. © 2013 Society of Chemical Industry     

Synthesis and characterization of chlorine‐containing flame‐retardant polyurethane nanocomposites via in situ polymerization

We have developed flame‐retardant polyurethanes (FRPUs) and polyurethane (PU) nanocomposites via in situ polymerization. Three series of thermoplastic elastomeric PUs were synthesized to investigate the effect of incorporating 3‐chloro‐1,2‐propanediol (CPD) and nanoclay on mechanical, thermal properties, and also resistance to burning. PU soft segments were based on poly(propylene glycol). Hard segments were based on either CPD or 1,4‐buthane diol (BDO) in combination with methyl phenyl di‐isocyanate named PU or FRPU, respectively. In the third series, CPD was used as chain extender also nanoclay (1% wt) and incorporated and named as flame‐retardant polyurethane nanocomposites (FRPUN). Mechanical properties and LOI of PUs and nanocomposites have been evaluated. Results showed that increasing the hard segment (chlorine content) leads to the increase in flame retardancy and burning time. Addition of nanoclay to CPD‐containing PUs leads to obtain self‐extinguish PUs using lower CPD contents, higher Young's modulus, and strength without any noticeable decrease in elongation at break. Investigation of the TGA results showed that copresence of nanoclay and chlorine structure in the PU backbone can change thermal degradation pattern and improve nanocomposite thermal stability. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation and intercalation have been well done. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and ionic conductive properties of polydioxolane–polyurethane‐based electrolytes

A series of polyurethanes (PUs) with different polyether soft segments [polydioxolane (PDXL), polyethylene glycol (PEG), or PDXL/PEG] were synthesized successfully, and solid polymer electrolytes based on PU/LiClO₄ complexes were prepared. The relations between structure and the ionic conductive properties of the PU‐based electrolytes were investigated by means of Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and complex impedance analysis. Results showed that the glass‐transition temperature (T_g) of PDXL–PU was lower than that of PEG–PU. Doped lithium perchlorate (LiClO₄) salt could be dissolved well in soft segments of PDXL–PU. The ionic conductivity of the PDXL–PU/LiClO₄ complex could reach a value of 2 × 10^?5 S/cm at room temperature without the addition of an organic plasticizer. The system with PDXL/PEG as a soft segment had a higher T_g and a lower ionic conductivity than the one with PDXL as a soft segment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 103–111, 2002     

Influence of ionic groups on the crystallization and melting behavior of segmented polyurethane ionomers

The isothermal crystallization kinetics and melting behavior of the soft segment in polyurethane (PU) ionomer/nonionomer based on PCL‐4000 (poly(ε‐caprolactone)) were investigated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). In general, the presence of ionic groups in PU ionomers can promote the formation of a more stable crystalline structure and lower the equilibrium melting temperature of the crystallizable phase. Comparison between the crystallization characteristics of PU nonionomers and ionomers suggests that the Coulombic Forces between ionic groups within hard segment can increase the crystallization rate and decrease the crystal size of soft segment when the total molecular weight (M_w) of PU ionomer is higher than ～71,000. On the other hand, the opposite effect of ionic groups on the crystallization rate is observed in PU ionomers with M_w below ～20,000. The DSC thermograms illustrate that the ionic groups can significantly enhance the microphase separation in PU ionomers with higher M_w values. By the control and manipulation of crystallization and microstructure formation in PU ionomer, it is possible to achieve shape memory PUs with superior physical property. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4603–4613, 2006     

Mechanical and surface properties of membranes prepared from waterborne cationic hydroxyl‐terminated polydimethylsiloxane/polyurethane surfactant‐free micro‐emulsion

With the action of catalyst and cosolvent, a series of hydroxyl‐terminated polydimethylsiloxane (HPMS) based polyurethane (PU) micro‐emulsion were gotten by surfactant‐free copolymerization. They were successfully prepared by reacting isophorone isocyanate, poly(tetramethylene glycol), and HPMS with N‐methyldiethanolamine (MDEA) as chain extender and trimethylolpropane (TMP) as crosslinker. After neutralizing with dimethyl sulfate and inversing the emulsion polymerization with deionized water, a series of microemulsions were obtained. The emulsions were then cast into membranes named as PU–HPMS. The mechanical properties and water absorption of the PU–HPMS were determined and simultaneously the effects of the content of hard segment, solvent, TMP, MDEA, HPMS, and the molecular weight of soft segment were studied. It is noticed that the tensile strength decreased and elongation at break increased in the HPMS/PU when compared with pure PU, which confirm that PU was end‐capped with PDMS. It is also noticed that water absorption increased in the HPMS/PU when compared with pure PU. As HPMS content increased from 0.0 to 25.0 wt %, the surface free energies decreased from 0.3446 to 0.2317 mN/cm and water absorption decreased from 11.2% to 0.14%. The surface free energies of the membranes were decreased by more than 32.76%, which demonstrate that the membrane surfaces have excellent water and oil repellency. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 40–46, 2006     

Synthesis and characterization of advance PA6‐b‐PDMS multiblock copolymers

Advance polyamide‐6‐b‐polydimethylsiloxane (PA6‐b‐PDMS) multiblock copolymers were first synthesized via the polymerization in bulk. Binary carboxyl terminated PA6 was served as the hard segment and PDMS modified with hexamethylene diisocyanate (PDMS‐NCO) was the soft segment. A series of PA6‐b‐PDMS copolymers based on different content and length of soft segments were obtained. Interestingly, Differential scanning calorimetry (DSC) studies revealed no obvious change in melting temperature after introducing PDMS segments to copolymers. The high melting temperatures indicated these copolymers possess potential applications in automotive industry that require high continuous use temperatures. DSC and transmission electron microscopy studies both demonstrated increasing the length and the content of the soft segment contributed to increasing of the degree of microphase separation. However, the improvement of thermal stability resulting from PDMS segments was also observed by thermo gravimetric analysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41114.     

Flexible cross‐linking by both pentaerythritol and polyethyleneglycol spacer and its impact on the mechanical properties and the shape memory effects of polyurethane

A series of polyurethane (PU) polymers cross‐linked laterally by pentaerythritol and polyethyleneglycol (PEG) spacers were compared with linear PU. The PU was composed of 4,4′‐methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol), 1,4‐butanediol (BD), pentaerythritol, and PEG‐200 as a spacer. PEG‐200 connected the pentaerythritol hydroxyl groups of two PU chains with MDI as a connecting agent. The phase separation between hard and soft segments was disrupted by the PEG crosslinking, and T_m did not change with an increase in cross‐linking content. Instead, the cross‐link density increased with an increase of pentaerythritol content. A significant increase in maximum stress compared with linear PU was attained, together with an increase in strain. The combination of both pentaerythritol and PEG‐200 in the PU resulted in the improvement of both stress and strain, unlike in the conventional cross‐linking method. The shape recovery increased to 90% and did not decrease after three test cycles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on polyethylene glycol/polydimethylsiloxane mixing soft‐segment waterborne polyurethane from different mixing processes

The surface structure and physical properties of polyethylene glycol series polyurethane (PEG‐PU) membranes, in which were introduced hydrophobic polydimethylsiloxane (PDMS) component by the procedure of PU blending or of soft‐segment copolymerization, were studied in this investigation. In the case of the blending process, the synthesized waterborne polyurethanes (WBPUs) of PEG–PU and of polydimethylsiloxane series polyurethane (PDMS–PU) were combined, whereas in the copolymerization process PEG and PDMS were taken as mixed soft segments to polymerize the WBPU. For the blending method, glass‐transition and melting temperatures increased rapidly when a small amount of PDMS–PU was added to PEG–PU and reached a maximum with 5% PDMS–PU mixed in. However, in the case of the copolymer method, thermal properties closely followed predicted values. From dynamic mechanical analysis studies it was found that a low PDMS–PU content ratio could increase the rubbery elasticity of PEG–PU membrane and improve its strength simultaneously in the blending method, and the copolymer method only caused PU to gain some natural complementary strength and elasticity. Electron spectroscopy for chemical analysis studies indicated that PDMS migrated to the surface much more easily in the blending method than in the copolymer method. The SEM studies also found that, in the blending method, the numbers of pores were less than those in the copolymer method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 233–243, 2003