摘要:

AbstractLight‐scattering second and third virial coefficients for benzene solutions (at 25°C) of two binary polystyrene mixtures, in which the molecular weight ratios of component fractions (essentially monodisperse) were 98 and 11.6, were determined as functions of polymer composition. The cross‐term virial coefficientsA12(for two different solutes 1 and 2),A112(for two same solutes 1 and one solute 2), andA122were evaluated from such functions. It was found that none of the existing theories forA12yield a consistent and quantitative description of our experimental finding. No theory is yet available forA112andA122, but the numerical values of these coefficients as estimated here are of interest in themse

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250101

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have investigated copolyesters based on a single aliphatic dibasic acid flexible segment and two rigid segments arising from 4,4′‐dihydroxybiphenyl (PB) and 2,6‐dihydroxynaphthalene (PN). Homopolyesters based on the latter rigid segment exhibit no enantiotropic mesophase for 5 ≤n≤ 8. The copolymers are designated PBN‐nwherenis the number of methylene units in the dibasic acid. From the temperature–composition phase diagram, the odd‐membered PBN‐5 and PBN‐7 exhibit only a nematic phase. The temperature range of the nematic phase decreases progressively with increasing mole fraction of naphthalene units. The even‐membered PBN‐6 and PBN‐8 exhibit a smecticSHmesophase and a newly induced nematic phase. Comparison with a previous study of copolymers involving a single rigid segment and two flexible segments reveals that the smecticSHphase is more easily disrupted, and converted to a less ordered nematic phase, by different rigid segments than by different flexible segments. The isotropization entropy of a series of nematogenic equimolar copolymers exhibits a marked odd–even effect, with the observed ΔSNIvalues being quite large for

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250102

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe transport properties of water in neat poly(aryl‐ether‐ether‐ketone) (PEEK) coupons (2 to 6 mm thick) were investigated by gravimetric and mass spectrometric methods. The solubility of water increases from 0.44 wt.% at 35°C to 0.55 wt.% at 95°C; the temperature coefficient is 8 kJ/mol (1.9 kcal/mol). The diffusion processes for sorption, desorption, and resorption at 35°, 50°, 65°, 80°, and 95°C are, within experimental error, the same. The activation energy for diffusion is 42.7 kJ/mol (10.2 kcal/mol). The diffusion process is classical Case I Fickian in the temperature region

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250103

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractInterpenetrating polymer networks based on polyurethane and polyurethane ionomer were studied using wide‐angle and small‐angle X‐ray diffraction. The polyurethane network is a multiblock polymer based on the trimethylolpropane adduct with 2,4‐toluene‐diisocyanate and poly(propylene oxide tetrahydrofuran) copolymer. Polyurethane ionomer represents a network formed from poly(propylene glycol) containing three OH side groups, 2,4‐toluene‐diisocyanate, 2,2′‐dimethylethanol‐amine, and 1,5‐dibromopentene. The network polymers are characterized by structure heterogeneity developed during microphase separation as a result of hard and soft block segregation. The interpenetrating networks investigated are amorphous systems over the whole range of compositions. They form a very complicated structure where the phase separation of polyurethane and ionomer takes place. It is important to note that phase separation leads to the appearance of microphase structure periodicity due to regular arrangements of microregions enriched by one of the components. The latter fact is considered to be a sign of spinodal phase separation

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250104

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractDielectric relaxation in three segmented polyurethane‐CaCO3composites was investigated between −70°C and +150°C in the 300 Hz to 100 kHz frequency range. Two of the polymers contained a polyacetal‐polyether soft segment, whereas the soft component of the third polymer was polypropylene oxide. The hard segments consisted of 4,4′‐diphenyl methane diisocyanate in two cases and toluene‐2,4‐diisocyanate in the third case.In parallel studies two calorimetric relaxations, designated α and α′, were observed for each sample and were determined to be glass transitions of the soft and hard segments, respectively. In general, the transition temperatures decrease with increasing filler content. High frequency, low temperature permittivities increase while low frequency, high temperature AC conductivities generally decrease with increasing filler content. The shift in the transition temperatures can be explained using the adsorption theory of filler‐polymer interactions and the densities of the samples. The interfacial polarization mechanism becomes important only above the α′ transition tem

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250105

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractA blend system of linear low‐density polyethylene (LLDPE) (ethylene butene‐1 copolymer) with high‐density (linear) polyethylene (HDPE) is investigated by differential scanning calorimetry (DSC), wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), Raman longitudinal‐acoustic‐mode spectroscopy (LAM), and light scattering (LS). For slowly cooled or quenched samples, one single endotherm is evident in the DSC curve which depends on the composition. No separate peaks are observed in the WAXD, SAXS, Raman‐LAM, and LS studies on the LLDPE/HDPE blends. This observation along with the fact that no peak broadening is observed suggests that these peaks are associated with the presence of a single component. In no case did we see double peaks or a broadened peak that might be associated with two closely spaced unresolved peaks. This suggests that segregation has not taken place at the structural levels of crystalline, lamellar, and spherulitic textures. A single‐step drop in the scattered intensity (IHv) as a function of temperature is seen in the LS studies. It is therefore concluded that cocrystallization between the LLDPE and HDPE components occurs. The mechanical and optical α, β, and γ relaxations of these blends are explored by dynamic birefringence. The 50/50 blend displays the intermediate relaxation behavior between those of the components in all α, β, and γ regions. This observation is reminiscent of the characteristic of

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250106

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractMelting and crystallization phenomena in blends of a linear low‐density polyethylene (LLDPE) (ethylene butene‐1 copolymer) with a conventional low‐density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light‐scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different t

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250107

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSmall‐angle light‐scattering (SALS) patterns were obtained during melting and crystallization of blends of linear low‐density polyethylene (LLDPE) with conventional low‐density polyethylene (LDPE). Quantitative measurements of these SALS patterns using a two‐dimensional optical multichannel analyzer apparatus (OMA2) indicate that the LLDPE which is miscible with the LDPE component in the molten state crystallizes first, forming volume‐filling spherulites. The LDPE then crystallizes within the preformed spherulites. These findings are supported by optical microscopy studies showing that the blend samples were volume filled with one kind of the spherulites having a radius comparable to that of the pure LLDPE. The SALS intensity curve changes with composition of the blends in a manner that may be interpreted by considering the orientation of crystals within spherulites. It has been observed that the spherulites in the blend have more diffuse boundaries as the LDPE content increases. The lattice spacing and long spacings in blends were obtained by wide‐angle and small‐angle x‐ray scattering, respectively. The SALS technique along with differential scanning calorimetry (DSC) is shown to be useful for determining the crystallization behavior of a crystallizable pol

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250108

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe dielectric properties of peroxide cross‐linked polyethylene–carbon black composite systems are described in the frequency range between 10 and 107Hz as a function of frequency and carbon black loading. Very high values for the dielectric constant were obtained when measuring conductive samples. A percolative model gives a suitable explanation, within experimental limits of the properties of the systems stud

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250109

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper reports the theoretical prediction and experimental verification of the connection between the yield stress of amorphous polymers and the physical aging phenomenon. The analysis reveals the existence of a fundamental relationship between the nonequilibrium glassy state and the thermally activated process controlling viscoelastic and plastic deformation. The results show that the volume relaxation and deformation kinetics share the same relaxation times, and that the activation energy for deformation belowTgis much smaller than previously mentioned in the literature. This indicates that the phenomenon of physical aging plays a very important role in the deformation and processing of polymers at low temperatures. The effect of quenching and annealing on the yield stress is described in terms of the mean energy of hole formation, the departure of volume from its equilibrium state, the distribution of hole energies, and lattice volume. The same set of molecular parameters obtained from the molecular kinetic theory of the glass transition and volume relaxation predicts the yield stress as a function of cooling rate, annealing time, temperature, and strain rate.

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250110

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY