摘要:

AbstractAn adaptation of the fracture toughness test method, theJ‐integral technique, is described within the general framework of polymer fracture behavior. It is shown that there is a strong interaction between different morphological parameters in the way they affect the fracture behavior of isotactic polypropylene (iPP). The fracture toughness decreases with increasing crystallinity at a fixed spherulite size. The fracture toughness also decreases slightly with increasing spherulite size at a constant crystallinity, but this may not be a pure spherulite size effect. The use of a nucleating agent results in a very fine spherulitic structure but facilitates crack growth and reduces the material toughness beyond the crack initiation stage. This suggests that the material behavior is dictated by the increase in crystallization temperature caused by the presence of the nucleating agent and not by the change in spherulite size. © 1995 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330901

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of aliphatic polyesters of sebacoyl chloride and poly(ethylene glycol) containing a different number of ethylene oxide groups was synthesized and characterized. These polyesters were complexed with lithium perchlorate to obtain a new class of polymer electrolyte. The relationships between the structure and properties of these polymer electrolytes were investigated. The main factor that affects the ionic conductivity in these systems was found to be the solvating capacity of the polyester for the lithium salt. These polymer electrolytes showed ionic conductivities up to 10−5˜ 10−4S/cm at 25°C. The mechanical strength was improved by cross‐linking, and the cross‐linked polyester complexed with a LiCIO4salt showed an ionic conductivity of 2 × 10−5S/cm at room temperature.7Li NMR spin‐spin relaxation and dielectric relaxation studies were also carried out to investigate the local environments and dynamics of ions in the polymer electrolytes. © 1995 John

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330902

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThermally stimulated current (TSC) and relaxation map analysis (RMA) were used to study the glass transitions and relaxation phenomena of the anisotropic and isotropic glasses for the semiflexible polyesters with various polymethylene spacers (n= 7 ˜ 10). TSC analysis indicated that the glass transition temperatures (Tg) of polymers at around 40 ˜ 50°C exhibited an apparent even‐odd behavior not only for the anisotropic glasses but also for the isotropic glasses. TheTgof the isotropic glass for the polymer with evennvalue was observed to be higher than those for the two neighboring polymers with oddnvalues. The anisotropic glass for the polymer with evennvalue had a lowerTgthan those for the two neighboring polymers with oddnvalues. The lower value was attributed to the configuration and orientation effects on the behavior of polarization. RMA revealed that the relaxation modes of the investigated polymers were also influenced by the configuration and orientation effects. The dipolar relaxation of the anisotropic glass for the polymer with oddnvalue occurred at a higher temperature and had a lower entropy (enthalpy) of activation than that of the isotropic glass for the same polymer due to the orientation effect. However, an inverse relation was found to occur for the polymer with evennvalue, which came from thetransconfiguration of the even polymethylene spacers. Finally, the thermokinetic properties evaluated by RMA (e.g., the final state after depolarization) correlated quite well with the results obtained by TSC. © 1995 John Wiley&Sons

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330903

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractWe reexamine the influence of statistical segment length asymmetry on the surface segregation of homopolymer blends in a mean field thread model of polymer melts. By developing numerical self‐consistent field solutions of the Edwards‐Helfand equations, we demonstrate that the component with the smaller value of the parameter β2=a2/(6ν) (ais the statistical segment length and ν is the segment volume) is enriched at a neutral, impenetrable surface. Qualitatively, this finding is in agreement with our earlier analytical work and with experiment. However, in contrast to our earlier work, we find that the absolute magnitude of the segregation is a sensitive function of the chain lengths of the two species and of the compressibility of the system. © 1995 John Wiley&So

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330904

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe gas transport properties of a series of polyarylates based on isophthalic acid have been examined. The polyarylates were synthesized from the following bisphenol monomers with and without tetrabromo substitution: bisphenol A, hexafluorobisphenol A, phenolphthalein, and fluorene bisphenol, to study the effects of tetrabromination in combination with varying the bisphenol connector group size and shape. Substitution of a tertiary butyl group at position five on the isophthalate ring was used to increase polymer permeability. Tetrabromination of the bisphenol maintains or increases gas permeability and significantly increases permselectivity particularly for the O2/N2gas pair as compared with the non‐brominated analog. The substitution oft‐butyl groups increases gas permeability by two‐to fourfold but lowers permselectivity. Most of the increase in permeability can be related to an increase in the diffusion coefficient for each gas. All the brominated polyarylates have gas transport properties superior to most known glassy materials for O2/N2separation with several materials close to a proposed empirical “upper bound” between permeability and selectivity. © 1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330905

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractWater transport in a polyketone terpolymer was analyzed performing both sorption and permeation experiments. Water vapor sorption tests were conducted at four temperatures (35, 45, 55, and 65°C) and at several activities. The analysis of sorption isotherms revealed the occurrence of water clustering. A reduction of the endothermicity of mixing as the amount of sorbed water increased was observed which is consistent with significant association of penetrant molecules in the polymer. Permeation experiments performed at 35°C at upstream pressures ranging from 4 to 25 Torr showed evidence of a reduction in water diffusivity as function of sorbed water concentration which is a typical indication of penetrant aggregation. © 1995 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330906

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractOver the past years, the equilibrium sorption of gases in polymers has been intensively studied. Mostly, glassy polymers were investigated because of their excellent selective mass transport properties. This work does not focus on the equilibrium sorption but on the kinetics to reach the equilibrium. We developed a new experimental method measuring the sorption‐induced dilation kinetics of a polymer film. Carbon dioxide and glassy, aromatic polyimides were chosen as model systems. Low‐pressure experiments demonstrate that the measured dilation kinetics represent the sorption kinetics. A significant delay between the sorption and dilation kinetics is based on the fact that dilation kinetics occurs simultaneously with the concentration increase in the center of the polymer film. High‐pressure experiments reveal significant differences in dilation kinetics compared to low‐pressure experiments. Generally, three regimes can be distinguished in the dilation kinetics: a first, fast volume increase followed by two much slower regimes of volume increase. The magnitude of fast and slow dilation kinetics strongly depends on the swelling history of the polymer sample. The results of the experiments are analyzed in the light of a model relating the fast dilation kinetics to a reversible “Fickian” dilation and the slower dilation kinetics to an irreversible, relaxational dilation. © 1995 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330907

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractCombination of differential scanning calorimetry, x‐ray diffraction, Fourier transform infrared, and C‐13 nuclear magnetic resonance observations made on the crystalline inclusion compound (IC) formed between polytetrahydrofuran (PTHF) and urea (U), together with their comparison to identical observations performed on bulk semicrystalline samples of PTHF, have permitted an analysis of the conformations, motions, and environments available to PTHF chains in both solid‐state phases. The isolated PTHF chains occupying the narrow channels of the PTHF‐U‐IC are highly extended, though small rotational deviations averaging 24° from the nearly all trans, planar zig zag conformation of bulk crystalline PTHF chains produce some significant differences in their behaviors. PTHF chains in PTHF‐U‐IC possess much greater mobility than bulk crystalline PTHF chains as evidenced by C‐13 spin lattice relaxation times,T1, 50 times shorter (1.5 s) than observed for bulk crystalline PTHF chains (75 s). FTIR observations are consistent with very little specific interaction between guest PTHF chains and host urea matrix molecules and result in similar spectra for bulk and IC PTHF, except for the presence of the CH2rocking vibration band at 745 cm−1observed for bulk PTHF. The absence of this band in the IC PTHF can be understood by considering the symmetry of the all trans, planar zig zag conformation of bulk crystalline PTHF chains, which prevents the CH2rocking mode from coupling with skeletal stretching and bending modes as occurs in the nonplanar, helical PTHF chains in PTHF‐U‐IC. © 19

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330908

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractInterdiffusion of polymer chains across particle‐particle interfaces in latex films is one of the key issues, because this further coalescence process usually controls the cohesive strength of the films. Here we examined local dynamics of polymer chains within latex films and showed that it is related to the occurrence of particle coalescence. For this purpose, structural and dynamic micromechanical properties of partly cross‐linked polymer films from styrenebutadiene (SB) copolymer latexes were investigated. The gel fraction of the emulsion copolymers was varied within a large range (15–90%) by adding different chain transfer agents during the polymerization process. The structure of the films was determined using small‐angle neutron scattering (SANS) and transmission electron microscopy (TEM). A qualitative description of the mechanism that likely triggers further coalescence in latex films is given, based on critical disjoining pressure exerted by particle cores on interfacial membranes. In addition, from dynamic micromechanical analysis (DMA) spectra, a key molecular parameter reflecting local segmental mobility was derived. Average diffusion coefficients of polymer segments were calculated and shown to be consistently related to the occurrence of particle coalescence as evidenced from SANS and TEM structural investigations. Finally, the noncovalent physical intermolecular interaction loci, which act as cross‐link knots, were shown to play a significant part in the restriction of the coalescence process, increasing the state of constraints encountered by free chain segments embedded in the covalent network. © 1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330909

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe complex Young's modulus,E*(ω), and the complex strain‐optical coefficient,O*(ω), were measured for polyisobutylene (PIB) over a wide temperature range near and above its glass transition temperature. The master curves could be constructed well for each function with the method of reduced variables. The shift factor,aT, forE*(ω) is the same as that forO*(ω). The ratio of the imaginary parts ofO*(ω) andE*(ω),O″(ω)/E″(ω), takes an extremum, which has never been observed for other polymers. The relation betweenO*(ω) andE*(ω) cannot be described by a modified stress‐optical rule (MSOR) which has been found valid for various polymers. The basic concept of the MSOR. i.e., the chain orientation and the orientation of flat monomer units in the stretch direction, is not sufficient to describe the behavior of PIB and another origin of stress, presumably due to the fluctuation of local stress, should be included. This term does not contribute to the birefringence. The main maximum of tan δ is ascribed to the relaxation of the chain orientation in contrast with many other polymers, such as polyisoprene and polycarbonate, for which the maximum of tan δ is ascribed to the rotational relaxation of monomer units. © 1995

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330910

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY