摘要:

AbstractAcoustic, opto‐acoustic, and x‐ray investigations have been performed in order to study the influence of irradiation, electrical poling, and mechanical orientation on the morphology of ferroelectric random copolymers of vinylidene fluoride and trifluorethylene {P[VDF/TrFE] (70/30)}. The influences of these different treatments on the molecular orientation distribution of the amorphous and crystalline phases are discussed, as well as their influences on the crystallinity of the material. The elastic stiffness and the related viscosity tensors of P[VDF/TrFE](70/30), the elastic stiffness modulus of the amorphous matrix, and the hierarchy of stiffness constants of the crystalline state have been determined. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310501

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractProton spin‐spin relaxation measurements and the corresponding second moments 〈ΔH2〉 of broad line spectra are reported for powder samples of homopolyesters of hydroxybenzoic acid (HBA) and hydroxynaphthoic acid (HNA) and for oriented tape samples of HIQ‐35, a terpolyester composed of HBA, isophthalic acid, and hydroquinone. These are reviewed in relation to previous results reported for related copolyesters of HBA and HNA. In particular, the values of 〈ΔH2〉 for isotropic samples were predominantly composition dependent and of little practical value for studies of detailed molecular structure. Orientation‐dependent second‐moment anisotropies, on the other hand, provide indirect insight into molecular conformation and orientation through comparison with results from detailed molecular models. The orientations of monomers are well described by the distribution function proposed by Bower; a quantitatively accurate description of the orientation distribution in cylindrically symmetric geometries requires only the Legendre polynomial coefficient 〈P2〉. Modeling results based on rotational isomeric state theory for chain segments of finite length and high degrees of orientation successfully reproduce the degrees of anisotropy observed in 〈ΔH2〉 for both HBA/HNA and HIQ polymers. The model provides a link between measures of orientation obtained at different molecular scales by mechanical analysis, wide‐angle x‐ray diffraction, and nuclear magnetic resonance spectroscop

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310502

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(N‐n‐butylitaconimide) was prepared by radical polymerization in benzene and in bulk at 60°C and was subsequently fractionated at 30°C with benzene and methanol as solvent and nonsolvent, respectively. Relationships between molecular weight and intrinsic viscosity (Mark‐Houwink‐Sakurada equations) in tetrahydrofuran, benzene, and toluene at 30°C are established. From the Burchard‐Stockmayer‐Fixman plot, the characteristic ratio of this polymer is determined, and local chain conformation is discussed in relation to the termination process in radical polymerization. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310503

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA series of vinyl alcohol/vinyl butyral copolymers was examined to assess the effect of internal hydrogen bonding on gas sorption and diffusion. Sorption and permeation measurements for carbon dioxide and methane were performed on four vinyl alcohol/vinyl butyral copolymers. Upon comparing the various data, it was found that hydrogen‐bonded copolymers exhibit a much wider variation in diffusion coefficient than non‐hydrogen‐bonded copolymers. The fractional free volumes of the studied copolymers were considerably lower than expected based on values of the diffusion coefficient. This may be due to the fact that predicted occupied volumes are too large and that the effect of internal hydrogen bonding is not accounted for properly. Using a relationship between infrared spectral shift and hydrogen‐bond length, fractional free volumes in the hydrogen bonded copolymers were correlated with the interatomic spacing associated with the hydrogen bond. This implies that the average length of a hydrogen bond can be used as a measure of chain packing in hydrogen‐bonded polymers. © 1993 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310504

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of structure on the sorption kinetics of water and of various organic solutes into polyimide (PMDA‐ODA) thin films was studied. The major techniques employed include measurements of sorption kinetics, density, and dielectric relaxation. More solute uptake, lower densities and higher diffusivities were observed for films cured at lower temperatures. By measuring both changes of mass and of density, the volume expansion of the polymer due to each solute was obtained; this was found to be proportional to the molar volume of the solute. The two dielectric relaxation peaks (denoted by γ1and γ2) due to water (and other solutes) were studied in detail to obtain the relevant activation energies and the separate dipole moments. While water and methylene chloride appear in both γ1and γ2configurations, methyl and ethyl alcohol appear mainly as γ2, while acetic acid is primarily γ1. It was concluded that the γ1configurations are relatively homogeneously distributed throughout the polymer, involving loose bonding to the polymer structure, while the γ2configurations involve small clusters, probably chains of molecules. © 1993 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310505

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe crystallization behavior of poly(ethylene terephthalate) both with and without sodium montanate, a crystal nucleating agent, has been studied using the microhardness technique. The kinetics of crystallization from the glassy state were investigated in real time by measuring the microhardnessHat different crystallization temperatures. Results are discussed in terms of the Avrami equation. Values of the Avrami exponentnof about 3 are observed for samples irrespective of nucleating agent. For samples with nucleant two crystallization ranges are observed: a first range which corresponds to a fast crystallization from nucleating agent particles and a second range which is associated with a slow self‐crystallization mode. New transitions evidenced by the presence of a small maximum inHas a function of annealing time and temperature are detected at temperatures aboveTgfor physically aged samples. The kinetics of this transition have also been examined. It is further shown that the presence of nucleating agent induces a hardening at room temperature which is similar to the effect produced by the physical aging of the samples belowTg. Finally, it is found that aging reduces the rate of creep of the material under the indenter. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310506

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractDepending on reaction conditions, the system cellulose–N2O4may give two different unstable crystalline compounds, one being an ester (cellulose trinitrite), the second, an adduct of cellulose and HNO3(the Knecht compound). For these compounds, mechanisms of the formation of the crystalline phase as a result of topochemical reaction and self‐organization are discussed. The different characteristics of structural transformations of the fiber under nitrosation and nitration are noted. The existence of polymorphic forms of the Knecht compound is suggested. These labile nitrogen‐containing compounds make possible the regeneration of cellulose in its various modifications (cellulose I, II, IV, or amorphous cellulose) from the cellulose–N2O4system. The formation of unstable compounds and their ability to crystallize in the reaction medium allows the passage from amorphous cellulose to its crystalline modifications II or IV under mild conditions. The causes of decrystallization of cellulose by N2O4are established. © 1993 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310507

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe freezing point depression of a solvent, imbibed by crosslinked polyisoprene networks, was studied. It is argued that in a swollen vulcanizate, polymer chains subdivide the solvent, creating zones too small for nucleation on cooling to occur at the normal freezing point of the solvent. The freezing point of the solvent is identified with the temperature at which nuclei can form in the swollen network. A linear relationship between freezing point and the volume fraction of rubber in the swollen gel is predicted for a uniformly crosslinked network. Such a relationship is shown to hold for gamma‐irradiated polyisoprene, but not for peroxide‐cured samples, where deviations from linearity are interpreted as indicative of nonuniformity in the network. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310508

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe polarization properties of an optical system, source–interferometer–polarizer–polymer film–detector, have been calculated. Using Mueller matrices, the intensity has been obtained as a function of polarizer angle. It is shown in some detail how polarization of the beam in both interferometer and detector optics distort the spectra. The contributions from the finite extinction ratio of the polarizer are also calculated and intensity variations caused by beam‐wandering are discussed. It is shown that the commonly used procedure for correcting the spectra is wrong. Better methods for correcting the spectra are proposed. The influence of a uniaxial refractive index on the data is discussed, and experimental methods that can deal with refraction effects are presented. © 1993 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310509

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe conditions of stability for weakly charged polyelectrolyte mixtures are analyzed from a scattering theory developed previously. In the thermodynamic limit of zero wave vectorq= 0, it is found that electrostatic interaction induces a compatibility enhancement which is discussed for various cases of charge distributions. The condition of microphase separation transition at the wave vector for which the scattering is a maximum is also discussed. © 1993 John Wiley&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310510

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY