摘要:

AbstractThe composition heterogeneity has been calculated for some block and graft copolymers. General relationships have been derived for a model of the poly(A‐g‐B) or poly‐(A‐b‐B) type fulfilling the assumption of random grafting. Numerical results have been calculated for special cases of particular interest. These include a copolymer having independent molecular weight contributions from units of species A and B (a special case of which is a block copolymer) and a graft copolymer where the grafting is not accompanied by crosslinking or degradation side reactions and no homopolymer B is formed. Two other model systems represent the effects of the presence or absence of both homopolymers. For the above models, the dependence of the composition heterogeneity on the structure‐determining parameters (average number of grafts in the molecule, polydispersity index of the molecular weight of the backbone and graft) is discussed. The heterogenities thus calculated are in many cases comparatively low. The composition heterogeneity of the system is in most cases increased by the presence of h

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110701

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractShape changes in the electron spin resonance spectrum of spin‐labeled polystyrene have been studied as a function of temperature in the range 77–340°K. Rotational correlation times have been calculated by using recent theories of slow‐motional effects on ESR spectra. Three models were used, namely, Brownian, moderate jump diffusion, and large jump diffusion. The moderate jump model gave correlation times in good accord with those found by other techniques for the δ relaxation in polystyrene. The relaxation was found to be independent of molecular

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110702

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe low‐strain‐rate tensile stress–strain properties ofcis‐ andtrans‐polybutadienes and ‐polyisoprenes, polybutadiene (cis/trans/vinyl), butyl rubber, and two SBR copolymers have been investigated from 77°K to up to 25°K below the glass transition temperatureTg. The energyEpdissipated in a stress–strain test in the region of previously reported secondary glass transitions is found to be a function of both the free volume f̄ T gat theTgand the dampingA 4 T gfrom 4°K toTg−25°K. The complex relationship between the impact strength, the free volume and the damping is briefly discussed. The effect of quenching through theTgwith liquid nitrogen was found to increase the value ofEpfor all materials. In a number of cases this increase was associated with the presence of internal crazes. The surface‐craze initiation stress is increased by the presence of surface residual compressive stresses caused by quenching. The internal tensile stresses balancing the surface compressive stresses together with the applied tensile stress cause internal dilatation and hence preferentia

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110703

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractA theoretical determination of the elastic modulus, the breaking strength, and breaking strain is made for a single infinitely long molecule of polyethylene (CH2)∞. These results are compared with those of a similar calculation on a molecule of polyethylene with a side chain attached. It is found that the presence of a side chain weakens the molecule by approximately 17

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110704

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThere have been several investigations dealing with the influence of the glass transition on the rate of radiation‐induced reactions, especially the crosslinking reaction. On the other hand, no correlation has been reported between secondary transitions and the variation of a reaction rate. In the present work, the degradation of poly(methyl methacrylate) in the temperature range of −196 to 160°C has been studied. Two breaks in the Arrhenius plot were found. The first one is located at −5°C and can be correlated with the γ transition, which has been assigned to the hindered rotation of the ester group whose scission initiates the degradation. It is concluded that the thermal excitation of the bond rotation can either increase the scission rate or decrease the recombination rate of reactive intermediates by expanding the cage of the surrounding molecules. If the second mechanism occurs, the rotation of the α‐methyl group should also be expected to favor the degradation. However, a second break in the Arrhenius plot was found at −130°C, and therefore significantly above the δ transition. The influence of this motion is therefore not clear. Certain radiation‐induced reactions of poly(vinyl chloride), known from literature, seem to be influenced by a secondary transition. It is concluded that secondary transitions may be significant for scission reactions. This suggests, with respect to the known significance of the glass transition, that the various types of molecular motions in polymers may influence radiation

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110705

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractHeat capacity values for melts of polystyrene, poly(methyl methacrylate), polypropylene, and polyethylene are calculated on the assumption that the total constant‐volume heat capacityCvis made up of two parts: one associated with molecular vibrations, and one, with holes. Numerical values of both components are given for a wide range of temperatures and compared with experimental data. For poly‐1‐butene insufficient data for complete evaluation are available, so that only the vibrational contribution could be disc

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110706

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe resistivity and dielectric constant for carbon black (5–12 vol‐%) in a nonconducting matrix have been measured over the range 20–90°C and dc to 2–105Hz. Styrene–butadiene rubber dissolved in tetracosane (22 parts SBR to about 70 parts wax) constituted the matrix. Wide variations in resistivity and dielectric constant with temperature and/or frequency were observed. A theory is presented to explain the experimental observations. It correctly predicts the qualitative features of the experimental results but its predictions are not quantitativel

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110707

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe relation between the fractive indexnand the density ρ of a liquid mixture is formulated as\documentclass{article}\pagestyle{empty}\begin{document}$$ {{\left( {n^{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-\nulldelimiterspace} 3}} - 1} \right)} \mathord{\left/ {\vphantom {{\left( {n^{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-\nulldelimiterspace} 3}} - 1} \right)} {\rho = }}} \right. \kern-\nulldelimiterspace} {\rho = }}\sum\limits_i {w_i R_{Si} } $$\end{document}wherewiandRsiare the weight fraction and the specific refraction, respectively, of componenti. The calculation of the specific refraction of straight‐chain polyethylene and polystyrene from data for pure compounds of low molecular weight is discussed. The result is applied to dilute solutions of polystyrene in toluene. The calculated values of (dp/dw)0and (d2ρ/dw2)0at three different temperatures are compared with measured values. The agreement is satisfact

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110708

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractResearch on liquid tellurium is reviewed and interpreted in an effort to obtain a consistent picture of the effect of pressure and temperature on the structure and properties of tellurium in the liquid state. Electrical resistance experiments on liquid tellurium support the existence of reaction boundaries in thep–Tdiagram. The boundaries are believed to identify stages in the reaction whereby the 2‐coordinate covalent chain structure transforms to a 3‐coordinate covalent network structure which eventually dissociates with pressure and temperature into a metallic system. The increasing liquid density associated with the molecular reaction is given as the cause of the maximum on theP–Tmelting curve. The melting curve maximum in tellurium is shown to be related to maxima in selenium and sulfur. Quenching tellurium from different liquid fields, delineated by reaction boundaries, resulted in materials with different x‐ra

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110709

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractDynamic light‐scattering experiments were performed on an ethylene–methacrylic acid copolymer and its sodium salt. The in‐phase ΔI′ and out‐of‐phase ΔI″ components of the light scattering were measured in a temperature range between 25 and 65°C for both samples. No transition is seen in this temperature interval for the acid, but a clear transition occurs around 40°C for the salt. This transition is associated with the softening point of the ionic domains pres

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110710

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY