摘要:

AbstractPhase heterogeneity of vulcanizates based oncis‐polybutadiene (cis‐Europrene) and SBR (Europrene 1500) blends obtained by radiation, thermal, two‐stage radiation‐thermal, and two‐stage thermal‐radiation processes was investigated by the radiothermoluminescence method. Unvulcanized blends of these polymers are found to be heterogeneous, exhibiting two glass transition temperaturesTg, which coincide with the values for the initial components. Following vulcanization, the difference between the twoTgvalues for a polyblend decreases. The decrease is more distinct for polyblends crosslinked at high temperatures. When the vulcanization temperature exceeds 140°C and the crosslink density (or 1/Mc) exceeds 5 × 10−5–1 × 10−4mole/cm3, the glass temperature ranges of the crosslinked blend are practically superimposed. Such crosslinked mixtures should be considered pseudo

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120701

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractMolecular relaxation processes in the 77–260°K interval and the structure of polyethylene melt‐crystallized under normal and high pressures have been studied. The positions of relaxation transitions and activation energy for molecular relaxation were determined by radiothermoluminescence. The most intense maximum in the glow curve of the sample crystallized under normal pressure is observed in the 200–240°K interval, i.e., in the range of the β transition. In this temperature interval the β relaxation activation energy changes from 15 to 25 kcal/mole. An increase of the pressure under which crystallization takes place results in a substantial decrease of the intensity of the β maximum. This indicates that the β transition of polyethylene is most probably due to the mobility of segments on the chain‐folded lamellar surface. For samples melt‐crystallized under pressure between 5000 and 7000 atm, relaxation transitions were found at 150 and 190°K. Various processes of molecular relaxation appear to be associated with the maxima observed on the polyeth

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120702

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe electrical dipole relaxation in PMMA has been studied by measuring thermostimulated depolarizing currents. A master curve for the segmental component of the dielectric constant has been constructed. The increment of the dielectric permittivity due to the α‐relaxation has been determined. The distribution function of the relaxation times and the average relaxation times in the region from 70°C up toTg= 105°C have been obtained. A way of describing the electret properties of the polymer is discu

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120703

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractIn order to elucidate the relationship between the dielectric main‐chain relaxation and molecular structure in rubbery polymers, we studied polyisobutylene, which is free from complicating factors such as stereoregularity, branching, isomerism, and crystallinity. On the basis of the known conformation in the crystal and conformations deduced in solution and in the glassy state, we assumed several probable conformations in the rubbery state, and estimated the motional units in terms of the modified Adam—Gibbs theory. A computer simulation based on the above results leads to the conclusion that the local conformation in the rubbery state retains a regularity similar to that in the crys

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120704

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractCopolymers of tetrafluoroethylene and propylene were prepared that contained 30–65 mole‐% of the former. Reactivity ratios of tetrafluoroethylene‐ and propylene‐ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures,Tg, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot ofTgversus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30–56 mole‐% of the former. Reactivity ratios of tetrafluoroethylene‐ and isobutylene‐ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained whenTgis plotted versus composition. Isobutylene‐containing copolymers having 45–54 mole‐% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120705

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe birefringence of an object is usually obtained from its retardation. For an object of variable refractive index and optic axis orientation, a matrix procedure should be used for relating the retardation to the birefringence. There are many cases in the literature where this correct procedure has not been used. The correct procedure is illustrated for the case of a polymer spherulite.

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120706

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe bivariate distribution function and the ring closure probability for a continuous wormlike chain derived by Gobush et al. and by Yamakawa and Stockmayer are translated into the two‐dimensional case. The results may be written in terms of Fourier series instead of spherical harmonics. Evaluation is carried out to terms of ordert−3, wheretis the ratio of the total contour length to the persistence len

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120707

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractTo establish optimum operating conditions for high‐speed gel‐permeation chromatography (GPC), the effects of column packing particle size, solvent flow rate, and column length on the separation efficiency have been investigated by using monodisperse polystyrene samples and polystyrene gel columns (TSK‐GEL column, Type‐H). Decreasing the particle size of the column packing reduces the time required to obtain a given resolution. Monodisperse polystyrene standards were measured under the optimum operating conditions established (gel particle size 5 μ, column length 2 ft, flow rate 2.5 ml/min). The molecular weight distribution of a polymer mixture was determined in less than 10 min with the same accuracy as by the conventional GPC. Such short analysis time enables one to use GPC for in‐plant quali

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120708

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe molecular weight distribution in various celluloses degraded by methanolysis has been studied by gel‐permeation chromatography. It is shown that the accessible portion of the sample apparently degrades preferentially into molecular fragments with a size distribution centered on species with a degree of approximately 8. This result is interpreted as indicating the presence of weak links in the cellulose chain

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120709

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY

摘要:

Abstractp‐Divinylbenzene has been polymerized by heating at pressures ranging from atmospheric to 2.5 GN/m2, and the moduli (Young's, shear, and bulk), density, and residual unsaturation of the products have been determined. The results show a marked effect of polymerization pressure upon density and upon the degree of conversion of the second double bond. Linear relations are indicated between modulus and either density or an intermolecular force function based on a 6–12 potential field. These results and others on the densification of polystyrene are discussed and it is concluded that the moduli of the poly‐p‐divinylbenzene samples prepared under these conditions are still at a level largely determined by intermolecular

ISSN:0098-1273    

DOI:10.1002/pol.1974.180120710

出版商:John Wiley&Sons, Inc.    

年代:1974

数据来源: WILEY