摘要:

Tetramethylpolyarylate-polyarylate (TMPAr-PAr) block copolymers of various block lengths were synthesized by the coupling reaction of hydroxy-terminated TMPAr and hydroxy-terminated PAr using triphosgene. The phase behavior of these block copolymers are discussed based on the thermal properties observed by differential scanning calorimetry (DSC). The thermal properties of binary blends of these block copolymers with PAr homopolymer or poly(styrene-co-acrylonitrile) whose acrylonitrile content is 9.5 wt% (SAN 10) were observed by DSC. The compatibilizing effect of the microphase-separated TMPAr-PAr block copolymer in PAr/SAN 10 blends was observed from thermal properties and morphology.

ISSN:0022-2348    

DOI:10.1080/00222349708220433

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Blends of poly(vinyl chloride) (PVC) and acrylonitrile-chlorinated polyethylene-styrene (ACS) copolymer were prepared by melt blending. Miscibility, phase behavior, and thermal stability were studied using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The DSC study showed that the blends have three glass transition temperatures (Tg). The blends exhibit a three-phase structure; a chlorinated polyethylene (CPE) rubbery phase was found to be dispersed in a continuous matrix consisting of both PVC-rich and SAN-rich phases. The interfaces between any two of the three phases are well bonded. PVC is immiscible with CPE in ACS but partially miscible with poly(styrene-co-acrylonitrile) (SAN with 25% AN content) in ACS. From theTgdata, the SAN appears to dissolve more in the PVC-rich phase than does the PVC in the SAN-rich phase. The apparent polymer-polymer interaction parameter [(x12)app] for the pair PVC/SAN was calculated to be 0.0055 at 170°C. TGA analysis revealed that there exists interaction during the degradation of the two polymers in the blends.

ISSN:0022-2348    

DOI:10.1080/00222349708220434

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Spherulitic growth rate and morphological studies carried out on a novel poly(ether ether sulfide) yielded dual spherulitic morphologies at all crystallization temperatures. Distinct populations of two kinds of spherulites were formed, with a population of coarse-textured spherulites exhibiting higher growth rate (Type II) than a population of fine-textured spherulites (Type I), at all temperatures studied. The growth rate dependence on temperature for the Type I spherulites was consistent with the theoretically predicted “bell-shaped” curve, indicating nucleation-controlled growth at temperatures close to the melting temperature and diffusion-controlled growth at temperatures closer to the glass transition temperature. The growth rate of the Type II spherulites, however, surprisingly did not exhibit any diffusion-controlled regime, with the growth rate increasing with decreasing temperature across the whole range of temperatures studied here. The above described phenomenon was found to be independent of the prior melt and crystallization history and nature of the substrate in all cases except one. The morphology of the different spherulites has been studied with a combination of optical microscopy, scanning electron microscopy, and atomic force microscopy. The Type II spherulites exhibited a coarser and more “open” morphology, with thicker bundles of fibrils and large interfibrillar gaps, radiating outward from the center of the spherulite. The Type I spherulites were found to exhibit curvature indicative of spherical behavior, whereas the Type II spherulites appeared to exhibit a flat disklike appearance; this finding is consistent with film thicknesses in that samples exhibiting Type I spherulites were films of thickness > 50 μm, whereas Type II spherulites were grown in films of thickness of ∼ 10μm. The differences in the growth rate and morphology between the Type I and Type II spherulites have, thus, been attributed to differences in film sample thickness; the causes behind such effects, however, still remain unclear.

ISSN:0022-2348    

DOI:10.1080/00222349708220435

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Samples of a diglycidyl ether of bisphenol-A (DGEBA)/4,4′-diaminodi-phenyl sulfone (DDS) system have been cured under various hydrostatic pressures from atmospheric pressure to 162 MPa at 150°C. In this study, the mechanical behavior of the pressure-cured samples was investigated by means of tensile creep tests. The creep tests were conducted at 144°C andTg-60°C (60°C below the glass transition temperature). The long-term creep compliance att= 3000 min decreased and then increased with increasing cure pressure. The sample cured at 35 MPa developed a long-term creep resistance that was 7.8 times greater than that of the sample cured at atmospheric pressure. The maximum long-term creep resistance occurred when cure pressure reached the critical value of about 60 MPa. The variation of the creep resistance of the pressure-cured samples is closely related to the average molecular weight between cross-links (Mc). This study demonstrated, once again, that hydrostatic cure pressure, like temperature, significantly influenced the mechanical property of the epoxy.

ISSN:0022-2348    

DOI:10.1080/00222349708220436

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Poly(γ-benzyl L-glutamate) (PBLG)-toluene solutions were quenched rapidly from an isotropic phase at elevated temperatures to the coexistence region of the isotropic and liquid crystal (I + LC) phases. The intensity of scattered light,Is, was measured with time after quenching at various scattering angles and quenching temperatures. The average molecular weights,Mw, of PBLG used were 1.0 × 105(PBLG-10), and 2.3 × 105(PBLG-23), and the ratios of the actual concentrations to the corresponding crossover concentration ø2/ø2* were equal to 1, 5, and 10 in the semidilute regime (hereinafter, PBLG-X-Y: X = 10 or 23; Y corresponds to ø2/ø2*). The spinodal decomposition (SD)-like phase separation was suggested to occur at the initial stage of gelation for quenched PBLG-10–1 and PBLG-10–5. In addition, the fractal dimensionDand the correlation length ξ at the later stage were determined according to a generalized Zimm relation containing the fractal dimension. For PBLG-10–1,Dand ξ were 2.6 and 610 nm, respectively, whereas the same physical quantities for PBLG-10–5 were respectively 2.7 and 250 nm. The former case indicates that the initial (modulated) phase-separation structure induced by the SD-like mechanism was frozen (or pinned), as it is at the later stage, and the latter indicates that the initial structure might grow by superposing a nucleation and growth (NG)-like phase separation on the SD-like process. There was no concrete evidence of SD in the other quenched PBLG samples.

ISSN:0022-2348    

DOI:10.1080/00222349708220437

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Changes in the fiber structure and properties of Japanese oak silk fibers treated with methacrylamide (MAA) were investigated. The cross-sectional area of the Japanese oak silk fiber impregnated with the MAA polymer was given by the sum of the cross-sectional area of the original silk fiber and that of the MAA polymer. Tensile strength and Young's modulus of the Japanese oak silk fibers impregnated with the MAA polymer decreased with increasing polymer add-on. Scanning electron microscopic observations of fracture surfaces of Japanese oak silk fibers impregnated with the MAA polymer revealed that the silk fibers were split into fibrils by the polymerization of MAA infused in the fibers. Wide-angle x-ray diffraction measurements suggested that the destruction of crystallites in the fibers occurred homogeneously, independent of the sizes of the crystallites, by the MAA treatment.

ISSN:0022-2348    

DOI:10.1080/00222349708220438

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Amorphous polystyrene-poly(α-methyl styrene) (PS/PMS) and polysty-rene-poly(vinyl methyl ether) (PS/PVME) miscible blends have been studied in detail by differential scanning calorimetry. A number of segmental dynamics characteristics, including the temperature dependence of motional activation energies over the range from the β relaxation region to the glass transition, the scale of motional unit events, and the degree of intermolecular cooperativity for segmental motion, have been determined. A number of peculiarities ofTgmanifestation as well as two types of segmental dynamics heterogeneity in the glass transition have been observed. They could be explained and predicted quantitatively, proceeding from the concept of the common segmental nature of the α and β relaxations in flexible chain polymers, as a consequence of a partial or complete breakdown of intermolecular cooperation (“individualizing”) or segmental motions. A linear correlation between the segmental dynamics activation energy and degree of intermolecular cooperativity has been found.

ISSN:0022-2348    

DOI:10.1080/00222349708220439

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Normal modes and their full dispersions are obtained for the right-handed α-helical poly(l-tyrosine). Optically active modes corresponding to the zone center and at the helical angle are assigned. Both the assignments and the force field are supported by the spectra of N-D species. In addition, modes corresponding to the regions of high density of states and other characteristic features of dispersion curves such as repulsion and exchange of character are discussed. Conformation sensitive modes of other α-helices are compared. Heat capacity is obtained from the dispersion curves via density of states and it is found in agreement with the measured data.

ISSN:0022-2348    

DOI:10.1080/00222349708220440

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor