摘要:

AbstractCharge‐mosaic membranes (CMMs) were prepared by modification of polyethylene (PE) with poly(styrene‐co‐divinylbenzene) or poly(vinylpyridine‐co‐divinylbenzene) and by selective insertion of cation and anion exchange groups in these copolymers. Changes of divinylbenzene content in the monomer mixture gave rise to differences in transport properties mainly through the change in water content. The CMMs were characterized by physico‐chemical properties of control membranes, i.e., they contained only one type of modified PE. Values were similar to those obtained from measurements carried out for CMMs. Diffusion coefficients determined in 0.1/0.02NNaCl solutions were in the range (1.5‐–5.7) × 10−7cm2s−1. These values indicate that transport of salt through these CMM's occurs by a typical mechanis

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191101

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe copolymerization of methyl methacrylate with small amounts (0.25‐1 mol %) of bis (4‐methacryloxybenzilidene)‐1,2‐diaminoethane in the pregelation stage was investigated. The mole fractions in the copolymers of the divinyl monomer, of the reacted vinyl groups of divinyl monomer, and of the totally reacted divinyl monomer units forming intermolecular crosslinks were determined experimentally and some other parameters were calculated from these quantities. The amount of intramolecular crosslinks, forming closed rings, has been shown to predominate over the amount of intermolecular crosslinks. The comparison of the experimental data with values calculated from Wesslau's theory, based on the classical concepts of copolymerization, reveals differences increasing up to an order of magnitude with rising content of the divinyl monomer. A major reason for this divergence appears to be the intramolecular cross

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191102

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe morphology of the ionomer resin from which Nafion perfluorinated membrane products are made was studied with wide‐angle and small‐angle x‐ray diffraction. A reflection observed in the small‐angle x‐ray scan from hydrolyzed polymer is attributed to ionic clustering. The effects of equiv wt, cation form, temperature, water content, and tensile drawing on this reflection were studied and are

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191103

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe relationship between drawing rate and drawing stress was studied for amorphous poly(ethylene terephthalate) (PET) under various experimental conditions. Three types of expriments were performed: simple drawing with necking at constant rate, drawing through a conical die, and drawing at constant stress. Under constant stress conditions a transition between two stable regimes of drawing can be observed. The transition occurs at a critical stress σcat which the rate of neck propagation changes by some orders of magnitude. Such a transition was found both below and above the glass transition of PET. With constant drawing rates instabilities of neck propagation were observed under certain experimental conditions. Such self‐oscillations, described by other authors, are not due to heat effects as has been proposed, but are related to the existence of the critical stres σc.Stress‐induced transitions in deformation behavior as in PET were observed for polypropylene and nylon 6 but not for polycarbonate. The results obtained by various methods including morphological studies do not support the assumption that the instabilities are caused by thermal effects due to the dissipation of deformation energy. Rather, a model is proposed which is based on the existence of a “spinodal transition” from the isotropic into the highly orien

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191104

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractOne can reproduce the observed accordion‐type laser‐Raman (ALR) scattering of highly drawn linear polyethylene if one assums that anygauchedefect in the crystal lattice which interrupts the all‐transconformation sequence of the molecular chain completely decouples the accordion‐type longitudinal oscillations of the two sections on both sides of the defect. Each oscillates independently of the rest. The length of the section, smaller than the full length of the straight chain between the crystal surfaces, determines the frequency of the ALR absorption. One such defect per five chain stems of the ideal crystal yields a straight‐length distribution which agrees sufficiently well with that derived from the ALR spectrum. Small‐angle x‐ray scattering very generally registers the resulting decrease of the electron density of the crystalline component without yielding more detailed information about the location and frequency of such

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191105

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractMean‐square dipole moments 〈μ2〉0for the (atactic) poly(4‐methyl‐1,3‐dioxolane) chain [CH2OCH(CH3)CH2O] were determined from dielectric‐constant measurements carried out on two fractions dissolved in benzene. Simple examination of the chain structure leads to the predictions that this polymer should have a significantly larger value of 〈μ2〉0than poly(1,3‐dioxolane) itself, but that 〈μ2〉0should be nearly independent of stereochemical structure. The first expectation is confirmed by the experimental results obtained, and the second by calculated results based on rota

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191106

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractStress relaxation in uniaxial extension and dynamic shear moduli G′ and G″ have been studied in networks of vinyl‐terminated poly(dimethyl siloxane) (PDMS) of five different molecular weights (Mnfrom 1800 to 29,200) crosslinked withcis‐dichlorobis (diethyl sulfide) platinum (II) and containing 10 and 15 wt % of two samples of high‐molecular‐weight unattached linear hydroxyl‐terminated PDMS (Mw700,000 and 950,000). TheMw/Mnratio of both the network prepolymers and the unattached linear species was approximately 2. In stress relaxation the stretch ratio was 1.25 or less and the shear relaxation modulus was calculated from the neo‐Hookean stress‐strain relation. In the dynamic measurements, the strain amplitude was 15% or less; after conversion to the timedependent shear relaxation modulusG(t) the two sets of measurements were combined and the contribution of the unattached speciesG1(t) was calculated by difference. After multiplication by (1 −v 22)−1G 0N/Ge, wherev2is the volume fraction of network,G 0Nis the plateau modulus of the uncrosslinked polymer, andGeis the equilibrium modulus of the network containing unattached molecules,G1(t) was compared withG11(t), the relaxation modulus was essentially the same in both environments. The relaxation was slower in the networks than in the uncrosslinked polymer by 1 to 2 orders of magnitude, and it increased gradually with increasingGe, which is a measure of total to pological obstacles represented by crosslinks plus trapped entanglements. A similar but less striking difference between relaxation in a network and in the homologous environment of a linear polymer was previously observed in end‐linked polybutadiene networks and the butadiene phase of a styrene‐butadiene‐styrene block copolymer. It appears that, in these systems where the topology of the obstacles is fixed, the reptation is severely restricted or else alternative modes of configurational rearrangement which contribute to relaxation in the unc

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191107

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe finite‐element method is applied to a craze model in order to estimate surface displacements and stresses of an isolated craze in a thin rectangular plate. The limitation of assuming linear‐elastic behavior of the craze fibrils is demonstrated by comparing computed profiles with published experimental ones. Accurate finite‐element estimates of craze surface stresses are obtained from the experimental displacement profile. The analysis is extended to the three‐dimensional case but the difference between the craze displacements at the surface of the plate and those at midthickness is too small to justify the considerable increase in computer time in comparison with that required for two‐dimensional

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191108

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractReplica and thin‐section electron microscopy was performed on a linear polyethylene fraction (Mw= 1.89 × 105,Mn= 1.79 × 105) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographic faults are also discus

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191109

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractBrillouin scattering is used to study hypersonic relaxation in 1,2‐polybutadiene andcis‐polyisoprene. The temperature of maximum loss was determined to be 125°C for a frequency of 5.0 GHz for polybutadiene and 100°C at a frequency of 5.9 GHz for polyisoprene. Hypersonic loss maxima are examined for many polymers and general conclusions are reached concerning the factors that can be used to predict the temperature of maximum

ISSN:0098-1273    

DOI:10.1002/pol.1981.180191110

出版商:John Wiley&Sons, Inc.    

年代:1981

数据来源: WILEY