摘要:

AbstractThe unique properties of polymers derive chiefly from their long‐chain nature, their high molecular weights, and their molecular weight distribution. The characterization of these properties has developed in steps, each followed by a period of consolidation and application. The most recent of these steps of advancement were the introduction of gel‐permeation or liquid‐exclusion chromatography (GPC), solving the problem of determining molecular weight distributions, and the calculation of the unperturbed dimensions of polymer chains. In the current period of consolidation following these advances, disturbing trends are evident. More use is being made of empirical but rapid techniques such as GPC, but less regard is being paid to the need for the calibration samples required to give them meaning. Absolute methods for molecular weight measurement, providing such samples, are practiced far less than a decade ago, and much special apparatus developed for these techniques is no longer commercially available. These methods are vital, and their continuing development and practice must be encou

ISSN:0360-8905    

DOI:10.1002/polc.5070550103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractSome of the factors which affect the accuracy of number‐average molecular weight determinations by vapor‐pressure osmometry are discussed. It is shown that care is required in the selection of compounds for calibration purposes to ensure that solute volatility effects do not lead to erroneous results. It is also demonstrated that, in certain systems at least, the calibration factor has a small but important dependence on the solute molecular weight over the molecular weight range examined (128

ISSN:0360-8905    

DOI:10.1002/polc.5070550104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThiokol HC 434 carboxyl‐terminated polybutadiene on hot storage in air increases in viscosity and molecular weight until, finally, gelation occurs. It was found that rate of aging can vary greatly from lot to lot. The difference in aging between lots is thought to be caused by a decrease in the catalytic activity of metal ion impurities due to chelation by varying amounts of glutaric acid remaining in HC 434 after manufacture. Stability of poorer‐aging HC 434 is improved by adding glutaric acid or other chelating age

ISSN:0360-8905    

DOI:10.1002/polc.5070550105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThis paper presents results which indicate that nonuniformities in the mixing and extrusion behavior of nominally standard grades of emulsion‐ and solution‐polymerized oil‐extended SBR are associated with variations in molecular weight distribution, which are not reflected by Mooney viscosity values.Generally, copolymers with broader molecular weight distribution have higher compound die swell, and lower rates of carbon black dispersion during mixing. Delta Mooney values and torque rheometer t' point tests were found to be of utility in predicting extrusion die swell and carbon black dispersion characteristics of oil‐exten

ISSN:0360-8905    

DOI:10.1002/polc.5070550106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractWe have measured the self‐diffusion coefficient, D, of serum albumin (by the open‐ended capillary method) and the mutual diffusion coefficient, Dm, for serum albumin solutions (by the capillary method, and in the ultracentrifuge) at concentrations up to 0.2 g°Cm−3. Our self‐diffusion data follow those of Keller et al. [J. Phys. Chem., 75, 379 (1971)], but we can find no experimental support for their contention that Dm= D at high concentrations. Indeed, our results closely follow the theoretical relation Dm= D (1 – cv)(1 + 2A2Me +…).Where c, v, A2, and M are, respectively, the concentration, partial specific volume, second virial coefficient, and molar mass of serum albumin.We have also studied the concentration dependence of the frictional coefficients in diffusion and sedimentation. The two frictional coefficients are equal only in very dilute solutions of s

ISSN:0360-8905    

DOI:10.1002/polc.5070550107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractComputer simulations of polymer chains in restricted environments were carried out by the Monte Carlo technique. The model investigated was that of a random‐flight chain that commenced at an impenetrable barrier. The effect of close packing of contiguous polymer chains and the likely effects of the self‐excluded volume of the segments on the thickness of the adsorbed layer were studied.The results obtained suggest that the extension normal to the interface of a random‐flight chain with no volume exclusion was seemingly hardly affected by the presence of lateral compressive boundaries, at least at the usual surface coverages studied experimentally. When the effects of volume exclusion were simulated, the extension normal to an impenetrable barrier increased. This implies that the effects of excluded volume are likely to be responsible for the experimentally observed expansion of polymers normal to the inte

ISSN:0360-8905    

DOI:10.1002/polc.5070550108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractGel‐point methods for the determination of the functionality of some of the most widely used types of industrial polyisocyanate and polyisocyanate derivatives have been investigated. No single method was applicable to all types, and the most suitable method for each type was determined.With aliphatic polyisocyanates such as N,N′,N‐tris(6‐isocyanatohexyl)biuret I and II b or c (derived from trimethylolpropane and diisocyanates), the most satisfactory method was gel‐point titration with amino‐terminated polyethers. This method was unsuitable for the more reactive aromatic polyisocyanates IIa (from trimethylolpropane and tolylene diisocyanate) or III (poly(methylene phenylene) polyisocyanate), but these could be gelled by reaction with water. Gel‐point condensations with polyamines could be used for the less reactive phenol‐ and ketoxime‐blocked polyisocyanates.Poly(carbamoyl sulfonate) (VI) could be gelled either by hydrolysis to a polyurea in the presence of excess tertiary amine or by reaction with a diamine in the presence of a slight excess of tertiary amine to neutralize the bisulfite released. In all the gelations studied, the functionalities depended on concentration as a result of intramolecular reactions; this is a possible source of error in functionality determinations, particularly in the

ISSN:0360-8905    

DOI:10.1002/polc.5070550109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe relationship between copolymer composition and comonomer composition for the freeradical copolymerization of vinyl chloride with sulfur dioxide, initiated by γ‐irradiation and by tert‐butyl hydroperoxide/methanol at low temperatures, is compared with the relationships calculated from various possible copolymerization mechanisms using a range of reactivity ratios and equilibrium constants. The copolymerization approaches Lewis‐Mayo behavior at low temperatures (–78°C), but this model is inapplicable at higher temperatures. Copolymerization models involving (i) a 1:1 comonomer complex as a third monomer, or (ii) a penultimate effect of SO2on SO2addition to the propagating chain, are satisfactory at – 78°C, when they are indistinguishable from Lewis‐Mayo behavior, and also at 0°C, but not at other temperatures. A depropagation model involving reversibility of three propagation reactions with different temperature dependences will, however, satisfactorily explain the observed behavior at a

ISSN:0360-8905    

DOI:10.1002/polc.5070550110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractTo overcome the very slow reaction rates of weak electrolyte ion‐exchange resins in neutral salt solutions, the resins must be used as microparticles. Ways of handling microparticles are outlined. The present study is aimed at the preparation of large composite particles containing basic and acidic polymers in domains which are clearly segregated so that minimum interaction between the sites of opposite character occurs. Because the domain size is small, rapid reaction rates are achieved. Resins which show this effect have been prepared from basic and acidic monomers by using blocking procedures involving counterions, which significantly reduce the association of the basic and acidic sites. However, although very rapid reaction rates are obtained, the ion‐exchange capacities of the products remain inferior to those of composites made by binding the active microparticles together with an inert binder, showing that substantial self‐neutralization has still taken place. Similar results are obtained with basic and acidic monomers by using precipitation techniques, which are aimed at grafting one monomer onto a precipitated macroradical prepared from the other mo

ISSN:0360-8905    

DOI:10.1002/polc.5070550111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe preparation of composite ion‐exchange or “no‐matrix” resins by polymerizing a mixture of basic and acidic monomers is a practical proposition only if some means can be found to minimize interaction between the monomers, so that the sites in the final polymer are not rendered inactive by internal salt formation. This paper reports one method of avoiding the strong interaction between the oppositely charged monomers by employing one or both of the monomers as an electrically neutral precursor. After carrying out the polymerization, the groups may be converted to a usable form by hydrolysis. The effect of solvent, the acid to base ratio, the degree of crosslinking, and the effect of the nature of the initiator on the preparation and properties of no‐matrix resins prepared using neutral acid precursors was studied; it was found that no‐matrix resins may be obtained with thermally regenerable capacities comparable to “plum pu

ISSN:0360-8905    

DOI:10.1002/polc.5070550112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY