不同后处理条件下聚萘二甲酸乙二酯纤维的结构变化

对不同纺速下制得的聚萘二甲酸乙二酯 (PEN)初生纤维进行了冷拉伸、定长热处理和热拉伸等后处理 .通过WAXS、DSC等测试研究了纤维中结构变化与后处理条件之间的关系 .结果表明 ,较低纺速下所制得的无定形初生纤维在低于Tg 温度下的冷拉伸时发生了应力诱导结晶 ,纤维中生成了α晶体 .同样的初生纤维在定长热处理过程中直至 2 0 0℃仍保持无定形结构 .这些结果说明施加应力相对于升高温度对于α晶体的生成更为重要 .而热拉伸样品中结晶结构的形成与初生纤维的结构有很大关系 ,低纺速下无定形初生纤维在热拉伸后形成α晶体 ,而高纺速下主要含有 β晶体的初生纤维经热拉伸后 β晶体会部分转变为α晶体 ,且 β晶转变为α晶的难易程度取决于初生纤维中 β晶的完善程度 ,初生纤维中 β晶越完善 ,热拉伸时 β晶体越不易转变为α晶体     

Biodegradable fibers of poly(3‐hydroxybutyrate) produced by high‐speed melt spinning and spin drawing

The effects of high‐speed melt spinning and spin drawing on the structure and resulting properties of bacterial generated poly(3‐hydroxybutyrate) (PHB) fibers were investigated. The fibers were characterized by their degree of crystallinity by differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS), their orientation by WAXS, and the textile physical properties. The WAXS studies revealed that the fibers spun at high speeds and high draw ratios possessed orthorhombic (α modification) and hexagonal (β modification) crystals, the latter as a result of stress‐induced crystallization. The fiber structures formed during these processes were fibril‐like as the atomic force microscopy images demonstrated. The maximum physical break stress, the modulus, and the elongation at break observed in the fibril‐like spin drawn fibers were about 330 MPa, 7.7 GPa, and 37%, respectively. The fibers obtained by a low draw ratio of 4.0 had spherulitic structures and poor textile physical properties. The PHB pellets were analyzed by their degradation during the processes of drying and spinning and by their thermal and rheological properties. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2841–2850, 2000     

Higher order structural analysis of stereocomplex‐type poly(lactic acid) melt‐spun fibers

The higher order structure of stereocomplex‐type poly(lactic acid) melt‐spun fibers of an equimolar blend of poly(L ‐lactic acid) and poly(D ‐lactic acid) was analyzed with wide‐angle X‐ray diffraction (WAXD) and birefringence measurements. Two different crystalline structures were observed in the fibers: α‐form homocrystals and stereocomplex crystals. The weight fractions of the two crystals were estimated with the WAXD integrated intensity data. The crystalline orientation factors were obtained from the WAXD measurements. Well‐oriented homocrystals formed during a drawing process at the crystallization temperature of the homocrystal. Drawing above this temperature caused the stereocomplex crystal to be formed. The crystalline orientation tended to be lower with increasing drawing temperatures. Through the combination of the intrinsic birefringence and the fractions of the α‐form homocrystals and stereocomplex crystals, the birefringence of the amorphous phase was evaluated. The amorphous birefringence stayed positive and decreased with increasing drawing temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 218–228, 2007     

Real‐time SAXS and WAXS study of the multiple melting behavior of poly(ε‐caprolactone)

The multiple melting behavior of poly(ε‐caprolactone) (PCL) was investigated by real‐time small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) measurements coupling with differential scanning calorimetry (DSC). Semicrystalline specimens prepared by a continuous cooling process showed lengthening of the Bragg period during the progress of double melting. A model of variable thickness of lamella was proposed to fit to the SAXS patterns and revealed that both the crystalline lamella and the amorphous layer contributed to the increase in Bragg period while the later dominated the contribution. The model of variable thickness although satisfied the SAXS data was unable to compromise the data from other probing tools. A modification of the model proposed that each lamella piling up to construct the stacks in the crystallites was itself nonuniform in thickness. The modification with the parallel occurrence of the mechanism of surface melting and crystallization successfully compromised the observations from SAXS, DSC, and optical microscopy and provided a new perspective for the explanation to lengthening of the Bragg period related to multiple melting behavior. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1777–1785, 2010     

Development of the morphology and crystalline state due to hybridization of reinforced toughened nylon containing a liquid‐crystalline polymer

A hybrid composite consisting of rubber‐toughened nylon‐6,6, short glass fibers, and a thermotropic liquid‐crystalline polymers (LCP) was investigated by the LCP content being varied. The thermal behavior, morphology, and crystallization behavior due to hybridization were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and wide‐angle X‐ray scattering (WAXS). DSC results indicated that the crystallinity of the glass‐fiber‐reinforced toughened nylon‐6,6 was reduced by LCP addition, particularly 5–10 wt % LCP. DMA data showed that the miscibility between the blended components was maximum at the 5 wt % LCP composition, and the miscibility decreased with increasing LCP content. SEM photomicrographs revealed information consistent with the thermal behavior on miscibility. It was also observed that the 10 wt % LCP composition showed predominantly an amorphous character with FTIR and WAXS. WAXS results indicated that LCP hybridization increased the interplanar spacing of the hydrogen‐bonded sheets of the nylon crystals rather than the spacing between the hydrogen‐bonded chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 549–559, 2003     

Crystalline structure of polyamide 12 as revealed by solid‐state 13C NMR and synchrotron WAXS and SAXS

The crystalline structure of polyamide‐12 (PA12) was studied by solid‐state ¹³C nuclear magnetic resonance (NMR) as well as by synchrotron wide‐ and small‐angle X‐ray scattering (WAXS and SAXS). Isotropic and oriented PA12 showed different NMR spectra ascribed to γ‐ and γ′‐crystalline modifications, respectively. On the basis of the position of the first diffraction peak, the isotropic γ‐form and the oriented γ′‐form were shown to be with hexagonal crystalline lattice at room temperature. When heated, the two PA12 polymorphs demonstrated different behaviors. Above 140 °C, the isotropic γ‐PA12 partially transformed into α‐modification. No such transition was observed with the oriented γ′‐PA12 phase even after annealing at temperatures close to melting. A γ′–γ transition was observed here only after isotropization by melting point. Various structural parameters were extracted from the WAXS and SAXS patterns and analyzed as a function of temperature and orientation: the degree of crystallinity, the d‐spacings, the Bragg's long spacings, the average thicknesses of the crystalline (l_c) and amorphous (l_a) phases, and the linear crystallinity x_cl within the lamellar stacks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3720–3733, 2005     

Small‐angle X‐ray scattering investigation of carbon nanotube‐reinforced polyacrylonitrile fibers during deformation

Structural changes during deformation in solution‐ and gel‐spun polyacrylonitrile (PAN) fibers with multi‐ and single‐wall carbon nanotubes (CNTs), and vapor‐grown carbon nanofibers were investigated using synchrotron X‐ray scattering. Previously published wide‐angle X‐ray scattering (WAXS) results showed that CNTs deform under load, alter the response of the PAN matrix to stress, and thus enhance the performance of the composite. In this article, we find that the elongated scattering entities that give rise to the small‐angle X‐ray scattering (SAXS) in solution‐spun fibers are the diffuse matrix‐void interfaces that follow the Porod's law, and in gel‐spun fibers these are similar to fractals. The observed smaller fraction of voids in the gel‐spun fibers accounts for the significant increase in the strength of this fiber. The degree of orientation of the surfaces of the voids is in complete agreement with those of the crystalline domains observed in WAXS, and increases reversibly upon stretching in the same way as those of the crystalline domains indicating that the voids are integral parts of the polymer matrix and are surrounded by the crystalline domains in the fibrils. The solution‐spun composite fibers have a larger fraction of the smaller (<10 nm) voids than the corresponding control PAN fibers. Furthermore, the size distribution of the voids during elongation changes greatly in the solution spun PAN fiber, but not so in its composites. The scattered intensity, and therefore the volume fraction of the voids, decreases considerably above the glass transition temperature (T_g) of polymer. Implications of these observations on the interactions between the nanotubes and the polymer are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2394–2409, 2009     

Crystalline β‐structure of PHBV grown epitaxially on silicate layers of MMT

The poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/montmorillonite(MMT) nanocomposites were investigated by wide‐angle X‐ray scattering (WAXS). The aim of the investigation was solution intercalation of MMT with PHBV. Beside the usual orthorhombic unit cell, a stable pseudohexagonal β‐structure of PHBV was obtained. Well known β‐structure has one common WAXS reflection (d = 0.480 nm), which corresponds to the mean distance of PHBV chains in the pseudohexagonal structure. The new β‐structure has two diffraction peaks in the WAXS pattern. It is a three‐dimensionally ordered crystalline structure oriented in parallel with the silica layers of MMT. The new polymorphic form is supposed to be growing on the layers of MMT. Its layers serve as primary nucleation centers for epitaxial growth of the β‐structure. After annealing, this polymorphic form of PHBV disappears and it is transformed into the more stable α‐form leading to an enhanced total crystallinity of the polymer comprised in the nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 751–755, 2009     

Polymer crystalline structure and morphology changes in nylon‐6/ZnO nanocomposites

The influence of ZnO nanoparticles on the crystalline structures of nylon‐6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ‐crystalline form in nylon‐6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon‐6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon‐6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon‐6 are ascribed to the reorganization of imperfect crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1033–1050, 2003     

Confirmation of a nanohybrid shish‐kebab (NHSK) structure in composites of PET and MWCNTs

Here, the confirmation of an oriented nanohybrid shish‐kebab (NHSK) crystalline structure in a series of composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNTs) is reported. The combined use of small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and thermal analysis has been used to investigate the morphology development in PET‐MWCNT nanocomposites under hot isothermal crystallization conditions. The MWCNTs act as both heterogeneous nucleating agents and surfaces (oriented shish structures) for the epitaxial growth of PET crystallites (kebabs) giving an oriented crystalline morphology. In contrast, the PET homopolymer does not show any residual oriented crystalline morphology during isothermal crystallization but gave a sporadic nucleation of a classic unoriented lamellar structure with slower crystallization kinetics. The results provide a valuable insight into the role of MWCNTs as nanoparticulate fillers in the morphology development and subsequent modification of physical properties in engineering polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 132–137     

Analysis of crystallization behavior and crystal modifications of poly(butylene‐2,6‐naphthalene dicarboxylate)

Information on the crystalline structure and the properties of poly(butylene‐2,6‐naphthalene dicarboxylate) (PBN) has not been well reported until now, but it is known that there are two different crystal modifications in PBN, as follows: one is formed in isotropic samples by annealing (α form); another appears by annealing with tension (β form). The relation between the crystal modifications and the kinetics of isothermal crystallization for PBN was investigated using in‐situ Fourier transform infrared spectroscopy (FTIR) and wide‐angle X‐ray diffraction (WAXD). The melting behavior of each crystalline form was also studied by means of FTIR and differential scanning calorimetry (DSC) measurements. From the analysis of the melt‐crystallized PBN specimens, the two crystalline forms coexisted in the isotropic samples melt‐crystallized at 230°C, but only the α crystal modification was observed in the films annealed at lower temperatures. In addition, it was revealed that, at 230°C, the β modification was formed only in the primary crystallization process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 561–574, 1999     

Structure and mechanical behavior of nylon‐6 fibers filled with organic and mineral nanoparticles. I. Microstructure of spun and drawn fibers

The crystalline structure and fibrillar texture of nylon‐6 fibers filled with nanosized particles were investigated using wide‐angle and small‐angle X‐ray scattering. As‐spun fibers filled with organic nanoparticles consisting of aromatic polyamide‐like hyperbranched molecules with amine‐terminating groups exhibited strong modification of both the molecular orientation and the crystalline structure compared with that of unfilled spun fibers. Montmorillonite‐filled fibers mainly exhibited orientation improvement. The differences are discussed in terms of the rheological and nucleating effects during spinning. Drawing at 140 °C involves structural changes that resulted in the three kinds of fibers having a similar crystalline form and molecular orientation. In parallel, after significant strain‐induced changes, the microfibrillar texture of the various fibers displayed subtle differences at the ultimate stage of drawing. The changes in the fibril long period and fibril radius as a function of draw ratio are discussed in terms of the two sequential deformation processes of microfibril stretching and microfibril slipping. The occurrence of interfibrillar strain‐induced cavitation is discussed in relation to the nature of the interactions between the filler and the nylon‐6 matrix. And, finally, the mechanical properties are discussed in relation to the filler–matrix interaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3876–3892, 2004     

Application of SSA thermal fractionation and X‐ray diffraction to elucidate comonomer inclusion or exclusion from the crystalline phases in poly(butylene succinate‐ran‐butylene azelate) random copolymers

Poly(butylene succinate‐ran‐butylene azelate) random copolyesters were thermally fractionated by successive self‐nucleation and annealing (SSA). The samples before and after SSA were analyzed by differential scanning calorimetry (DSC) and X‐ray diffraction (WAXS and SAXS). WAXS results indicate that a small degree of comonomer inclusion is present in the crystalline phases that are formed in the copolymers depending on composition: a PBS‐like unit cell or/and a PBAz‐like unit cell, thus confirming the isodimorphic behavior of the samples. SSA on the other hand demonstrated that the degree of comonomer exclusion during crystallization is far larger than comonomer inclusion, as judged by the increase in fractionation degree with compositions leading to the pseudo‐eutectic point. Furthermore, WAXS, SAXS, and SSA results show that the isodimorphic behavior is not highly dependent on kinetic factors, as the degree of comonomer inclusion or exclusion in the samples was not significantly altered by SSA thermal fractionation, a thermal treatment that promotes annealing and molecular segregation of defects to the amorphous regions of the material. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2346–2358     

Plasticization and cocrystallization in LLDPE/wax blends

The structure and thermal properties of linear low‐density polyethylene (LLDPE)/medium soft paraffin wax blends, prepared by melt mixing, were investigated by differential scanning calorimetry (DSC) and small‐ and wide‐angle X‐ray scattering (SAXS and WAXS). The blends form a single phase in the melt as determined by SAXS. Upon cooling from the melt, two crystalline phases develop for blends with more than 10 wt % wax characterized by widely different melting points. The wax acts as an effective plasticizer for LLDPE, decreasing both its crystallization and melting temperature. The higher melting point crystalline phase is formed by less branched LLDPE fractions. On the other hand, the lower melting point crystalline phase is a wax‐rich phase constituted by cocrystals of extended chain wax and short linear sequences of highly branched LLDPE chains. The presence of cocrystals was evidenced by standard DSC results, successive self‐nucleation and annealing (SSA) thermal fractionation and by the detection of a new SAXS signal attributed to the lamellar long period of the cocrystals. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1469–1482     

Structure development of polyamide‐66 fibers during drawing and their microstructure characterization

Structure development during drawing was studied for three sets of polyamide‐66 (PA66) fibers with density, optical microscopy, wide‐angle X‐ray diffraction, and Fourier transform infrared spectroscopy. The crystallinity, estimated by density measurements, remained virtually constant with increasing draw ratios, indicating that stress‐induced crystallization did not occur for the PA66 fibers drawn at room temperature, but there was a rapid transformation from a hedrite morphology to a fibrillar one. The absence of stress‐induced crystallization differed from the behavior of polyamide‐6, and this was attributed to the stronger hydrogen bonding between polyamide chains and the higher glass‐transition temperature of PA66. Polarized infrared spectroscopy was used to measure the transition‐moment angles of the vibrations at 936 and 906 cm^?1, which were found to be 48 and 60°, respectively. The crystalline orientation was estimated from the band at 936 cm^?1, and the increase with an increasing draw ratio was in close quantitative agreement with X‐ray diffraction data; this showed that infrared spectroscopy could be used reliably to measure the crystalline orientation of PA66 fibers. Because we were unable to obtain the transition‐moment angle of the amorphous bands, the amorphous orientation was obtained with Stein's equation. The amorphous orientation developed more slowly than the crystalline orientation, which is typical behavior for flexible‐chain polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1940–1948, 2002     

Microstructural investigation of high‐speed melt‐spun nylon 6 fibers produced with variable spinning speeds

The structural details of high‐speed melt‐spun nylon 6 fibers at spinning speeds ranging from 4500 to 6100 m/min were investigated by solid‐state proton nuclear magnetic resonance (¹H NMR) spectroscopy, density and birefringence measurements, differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). The analyses of the proton spin‐lattice relaxation times in the rotating frame and correlation times confirmed the existence of three different phases, the immobile crystalline, intermediate rigid amorphous, and mobile amorphous regions, in the fiber sample. At spinning speeds lower than 5200 m/min, the portion of the crystalline phase increased at the expense of the rigid amorphous region and then reached a plateau afterward, from which the mobile amorphous portion increased. Combined analyses of density and birefringence measurements, DSC, and XRD in conjunction with NMR results indicated that the formation of the γ crystal became predominant compared to that of the α crystal. The orientation factor of the crystalline phase increased slightly with increasing spinning speed, whereas the amorphous orientation factor decreased because of the increase of the purely amorphous region. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1285–1293, 2000     

Annealing behavior of gel‐spun polyethylene fibers at temperatures lower than needed for significant shrinkage

The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003     

Crystallization and thermal properties of PLLA comb polymer

Poly(L ‐lactide) (PLLA) on poly(2‐hydroxyethyl methacrylate) (PHEMA) backbone was prepared by a combination of atom transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). The structure of the comb polymer was analyzed by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), and differential scanning calorimetry (DSC). WAXD result indicates that the comb polymer has α crystalline modification with a 10₃ helical conformation. Lamellar parameters of the crystalline structure were obtained by one‐dimension correlation function (1DCF) calculated from SAXS results. The calculations show that the thickness of crystalline layer is controlled by annealing temperature and comb structure. DSC was applied to study kinetics of the crystallization and melting behavior. Two melting peaks on melting curves of the comb polymer at different crystallization temperature were detected, and the peak at higher temperature is attributed to the melt‐recrystallization. The equilibrium melting temperature is found to be influenced by the comb structure. In this article the effects of the comb structure on Avrami exponent, equilibrium melting point and melting peak of the comb polymer were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 589–598, 2008     

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3‐bis[4‐(4′‐aminophenoxyl) cumyl] benzene

The double melting behavior of a thermotropic liquid crystalline polyimide was studied by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). This liquid crystalline polyimide exhibited a normal melting peak around 278 °C and transformed into a smectic A phase. The smectic A phase changed to nematic phase upon heating to 298 °C, then became isotropic melt around 345 °C. The samples annealed or isothermally crystallized at lower temperature showed double melting endotherms during heating scan. The annealing‐induced melting endotherm was highly dependent on annealing conditions, whereas the normal melting endotherm was almost not influenced by annealing when the annealing temperature was low. Various possibilities for the lower melting endotherm are discussed. The equilibrium melting points of both melting peaks were extrapolated to be 283.2 °C. Combined analytical results showed that the double melting peaks were from the melting of the two types of crystallites generated from two crystallization processes: a slow and a fast one. Fast crystallization may start from the well‐aligned liquid crystal domains, whereas the slow one may be from the fringed or amorphous regions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3018–3031, 2000     

Structure–dynamics relationships of the α‐relaxation in flexible copolyesters during crystallization as revealed by real‐time methods

The evolution of the α‐relaxation during an isothermal crystallization process of a series of flexible copolyesters of hydroxybutyrate (HB) and hydroxyvalerate (HV) has been followed in real‐time by wide‐angle X‐ray scattering and dielectric complex permittivity measurements. The change of the dielectric parameters with crystallization time can be phenomenologically described in terms of the Havriliak‐Negami equation. The dielectric strength follows a sigmoidal‐shaped pattern similar to that shown by the crystallinity. A reduction of the overall mobility with crystallization time of the polymeric chains in the amorphous phase has been observed. This slowing down effect depends on the HV molar content. The influence of the chain flexibility on the crystalline‐induced restriction has been discussed in the light of similar studies carried out with more rigid polymers. Dielectric experiments suggest that the progressive immobilization of polymer segments as crystallization proceeds cannot be exclusively associated with the amount of crystalline material. Differences in microstructure, depending on the HV molar content, seem to be responsible for the observed behavior. The progressive broadening and symmetrization of the α‐relaxation with increasing crystallization time has been explained as due to a restriction of the large‐scale motions of the polymeric chains, as the material is being filled in with crystals. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 37–49, 1999