摘要:

AbstractInitial relaxation times determined by the initial decay rate of the time correlation function of scattered light are calculated for the once‐broken rod model (two rigid rods of equal length connected by a universal joint) following the Fujiwara–Saito theory. The coefficientCdescribing the initial angular dependence of the first cumulant of the correlation function is also calculated. The results are compared with Pecora's results based on the Yu–Stockmayer theory for this model; and it is shown that the Fujiwara–Saito theory gives reasonable

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241101

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe viscometric behavior of maleic acid‐vinylpyrrolidone copolymer systemsp(MA–co–VP) were studied in dilute solution. The weight‐average molecular weights of fractionated copolymers were determined by gel permeation chromatography. Viscometric relations were determined in aqueous salt solutions and in organic solvents. Two theta‐conditions were found forp(MA–co–VP): in 0.968 M Na2SO4, and in a DMSO/acetone mixture, 35.6/56.4 (v/v) at 25°C. The conformational and thermodynamic parametersKΘandBwere evaluated from viscosity data in good solvents using the Stockmayer–Fixman and Berry extrapolations. A linear variation ofBwith the salt concentration was observed. The electrostatic (Be) and nonelectrostatic (Bo) contributions toBwere estimated. It was found thatBe>Bo, and this was attributed to the hydrophylic nature ofp(MA–co–VP) copolymers. The latter would reflect a greater influence of the electrostatic interaction on the hydrodynamic behavior of this polymer. The electrostatic (α η3), and the nonelectrostatic lim  C  s→∞(α3− 1) contributions to the expansion factor α η3were determined. It was found that α ηe3is a function of (

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241102

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe finite element method is applied to contours (measured by interferometry) of craze zones in front of stationary crack tips in polymethylmethacrylate (PMMA) in order to compute the stress distribution. The stress along the craze zone has its maximum at the crack tip, being about twice that predicted by the Dugdale model; and it decreases at first sharply and then more gradually, being almost constant as the craze tip is approached. Stress distributions, in a growing craze at the still stationary crack tip, at various times can be combined in a normalized curve. Craze stresses relax with time as the craze continues to propagate in a stable manner. When the specimen is unloaded, the craze stress is compressive near the crack tip, but is tensile at the craze tip and for most of the craze length. Analysis of measurements made during a loading cycle establishes minimum stress intensity levels at which no fibrils are in compression. The levels are different for increasing and decreasing loads, and it is found the craze stresses are tensile for most of the cycle. Throughout the cycle, there is an excellent correlation between the average craze stress and the theoretical stress predicted by the Dugdale model.

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241103

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractPoly(γ‐benzyl‐L‐glutamate) (PBLG), was utilized as a surface coating agent in order to obtain parallel molecular orientation in thin layers of PBLG liquid‐crystalline solutions confined between coated surfaces. It was found that in a thickness range much larger than the cholesteric pitch value, the texture was predominantly planar cholesteric. At film thickness comparable or smaller than the pitch, isotropic spherulites developed from a homeotropic nematic phase. Because of the coupling between the solution concentration and nematic director, as well as large differences in the elastic moduli of PBLG liquid‐crystalline solutions, the long‐range intermolecular interaction was unfavorable. Competition between parallel orientation induced by the surface coating of PBLG and inherent perpendicular orientation induced by PBLG molecules in the bulk would favor a short‐range helix‐coil transition mechanism, which results into a reentrant

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241104

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractPolycarbonate is known to crystallize thermally, but only slowly and to a limited (25%) extent. The melting points reported exhibit a wide variation. We have found that the melting temperature of polycarbonate may be drastically increased by employing a sequence of vapor‐induced crystallization and annealing treatments. The crystals formed by the treatment with organic vapor act as a nucleation or precursor state for further crystallization into larger, more perfect lamellae. An initial peak melting temperature of 195°C has been annealed up to 239°C, and then to 295°C by a double‐heat treatment. This sample is 60% crystalline, based on heat‐of‐fusion calculations. An equilibrium melting point of 335°C has been obtained for PC from an extrapolation of reciprocal lamella

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241105

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe Flory–Huggins lattice‐theory expression for solvent activity in a polymer‐solution is commonly used to calculate the thermodynamic interaction parameter χ with the aid of experimental data from vapor pressure osmometry. This expression assumes that χ is independent of composition. However, experimental data for a variety of polymer‐solvent mixtures indicate that χ exhibits an appreciable concentration dependence. A group contribution method, UNIFAC (UNIQUAC Functional‐Group Activity Coefficients) incorporating the free‐volume correction of Oishi and Prausnitz is used to predict the dependence of χ on solvent concentration. Agreement with previously reported experimental data is within 15%. Calculated values of χ obtained from the Flory–Huggins expression for solvent activity and from the corresponding Gibbs free energy of mixing (which does not assume that χ is independent of composition) are compared. Calculations based on the Gibbs free energy of mixing predict a somewhat larger value of χ relative to those based on solvent activity. The specific Gibbs free energy of mixing for polystyrene‐solvent mixtures is calculated using the UNIFAC model, and is found to represent qualitatively the phase equilibrium behavior. Quantitative discrepancies are observed, however, for the polystyrene‐acetone system in light of the actual experimental solubility reported by Suh and Clark (20). Most of the thermodynamic predictions for polymer‐solvent systems investigated herein are correlated qualitatively with the relative mismatch between solubility par

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241106

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe influence of morphological transitions on the hydrogen‐bonding behavior of polyurethanes is investigated by simultaneous measurements of Fourier‐transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The materials examined are a noncrystalline polyurethane hard segment, a crystallizable polyurethane hard segment, and a segmented polyurethane block copolymer containing crystallizable hard segments. Integrated absorbance data show that the hydrogen‐bonding behavior is insensitive to crystalline transitions within the hard segment microdomains, but that it does reflect morphological transitions in the block copolymer that are associated with intersegmental mixing. In addition, the spectral data show conclusive evidence for reversal of the urethane reaction at high tempera

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241107

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractNew results for isotactic polystyrene/cis‐decalin gels are presented that suggest that a simple fringed micellar model of the gel may not be appropriate. In measuring the room temperature compressive modulus of gels formed at −20°C, it was found that, not only do the gels exhibit significant stress relaxation but also that the isochronal modulus‐concentration diagrams exhibit abrupt changes in modulus (reduced stress) over narrow ranges in concentration rather than the smooth curves (straight lines) typical of swollen rubber and fringed micella

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241108

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractInfrared absorption by polymeric solids is generally anisotropic due to orientational effects induced by industrial processing and fabrication. The isotropic‐equivalent or structure‐factor spectrum of a sample can be computed from the absorbances along the three principal axes of the absorption ellipsoid. Experimentally, this is accomplished by a tilting procedure which has been computer interfaced for precise angular control. The technique is applied to poly(vinyl acetate) (PVAc) and poly(ethylene terephthalate) (PET). The effects of refractive index dispersion, fringe distortion, reflection, and birefringence are evaluated in terms of the thickness direction calculation. Error spectra based on sample symmetry are generated, and the limits of accuracy of the tilting technique are establis

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241109

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe techniques of polarized infrared spectroscopy and sample tilting are applied to one‐way drawn poly(ethylene terephthalate) (PET) films to calculate the trichroic absorption as a function of frequency. Of specific interest in this study is the distribution of vibrational modes in the plane transverse to the draw direction. The rotational isomeric content of the films is found by the method of least squares and compared with a density‐method prediction of crystallinity. A two‐phase model to describe PET morphology in the oriented state is examined and found to be inadequate. The segmental orientation as a function of strain is followed with five conformationally sensitive infrared modes. High segmental orientation is found in thetransconformers of both amorphous and crystalline phases. Little net segmental orientation in thegaucheconformers of the amorphous phase o

ISSN:0887-6266    

DOI:10.1002/polb.1986.090241110

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY