摘要:

AbstractSorption of water vapor by oligomeric homopolymers and triblock copolymers of ethylene oxide and propylene oxide, and by polyurethanes and polyurethane ‐ ureas derived from them is discussed. While the sorption isotherms (plots of ψ1vsa1, where ψ is he volume fraction of sorbed water anda1is activity) for most polymers investigated here are smooth and convex towards the abscissa, those found with polyurethane‐ureas containing long hard blocks have a “toe” at low activities. The plots ofa1/ψ1vsa1are shown to facilitate the analysis of data and the interpretation in terms of the D'Arcy‐Watt theory.Smooth isotherms are fitted by a simple equation with two parameters. The first is related to the limiting value, χ0, (at ψ1→ 0) of the χ parameter characterizing the polymer‐water interaction. The dependences of χ0on the polymer composition (content of hard segments or oxyethylene units) can provide information on the interaction between hard and soft segments.The second parameter is used in the computation of parameters characterizing the clustering tendency of water molecules. This tendency depends mainly on the content of oxypropylene units but is also raised by urethane or urea groups, though not so much as by

ISSN:0258-0322    

DOI:10.1002/masy.19920580103

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe study of associating polymers is complicated by the fact that at a finite concentration only an apparent molar mass is directly measured. This apparent molar mass deviates from the true one because of thermodynamic interaction. In a good solvent the repulsive interaction can be fully described in terms of the second virial coefficient, which can be measured at very low concentrations, and a correction can be made for the true molar mass. The technique has been successively applied to β‐galactosidase in a phosphate buffer and to cellulose 2,5‐acetate in acetone.The gel point could be determined, and critical behavior was found in very good agreement with percolation prediction. Two other methods were employed and tested. One is based on the condition that the longest relaxation time must diverge at the gel point, and correspondingly the translational diffusion coefficient should go to zero. The second criterion consists of the prediction that power law behavior should be observed for the time correlation function of dynamic light scattering as well as for the frequency dependent storage and loss moduli.These predictions were indeed found to hold for two polysaccharides which form thermoreversible gels in water at a fairly low salt concentration. The two polysaccharides are the Tamarind seeds polysaccharide in 1M Na2SO4and an exopolysaccharide from Rhizobium leguminosarum, strain 8002 in 0.1M NaCl solutions respecti

ISSN:0258-0322    

DOI:10.1002/masy.19920580104

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA theoretical interpretation of the dissociation behavior of weak polyacids is given. Incorporation of conformational variability in the free energy of a polyelectrolyte system extends the validity of the counterion condensation theory to cases in which cooperative transitions and/or aggregation phenomena take place. Comparison of the theoretical predictions with experimental data on ionic polysaccharides, either natural or derivatives, is presented.

ISSN:0258-0322    

DOI:10.1002/masy.19920580105

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractMany binary polymer mixtures, where at least one of the components is a copolymer, are capable of forming miscible blends within certain restricted ranges of compositions of the copolymers. The segmental interaction parameters χij can be determined from many of these systems when the phase boundaries are established, and can be used to predict miscibility in other blends. Determination of χij parameters is illustrated for a number of different copolymer mixtures and the ability to predict and map the miscibility regions in other blends is demonstrated. The technique has been extended to ternary copolymer systems with satisfactory result

ISSN:0258-0322    

DOI:10.1002/masy.19920580106

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe scattered light is very sensitive to the presence of supermolecular structures in polymer solutions, offering the possibility to study structure formation in situ by classical light scattering and to characterize the generated particles. An improved analysis of light scattering data yields information on the structure type, polydispersity of the systems, particle mass and size as well as the degree of swelling. The flocculation process of ampholytic modified poly(acrylonitrile) was investigated in dependence on the pH‐value and the content of different salts in the solvent. Results obtained give a deeper insight into the flocculation mechanis

ISSN:0258-0322    

DOI:10.1002/masy.19920580107

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractAs an extension of our previous work, attempts were made to establish fundamental relations giving the spinodal curve (SC), the critical solution point (CSP), the cloud point curve (CPC) and the shadow curve for quasi‐binary systems of multicomponent polymers 1 and 2 (P1/P2) and quasi‐ternary systems consisting of multicomponent polymers 1 and 2 in a single solvent (P1/P2/S). The procedure of computer experiment based on the above fundamental equations derived was also attempted to be established. The systematic computer experiments were carried out to examine the effects of the molecular characteristics of polymers and the mutual interaction parameter on the phase diag

ISSN:0258-0322    

DOI:10.1002/masy.19920580108

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractDevelopment of phase‐separated morphologies has been studied in polymer blend solutions and forced mixtures of highly immiscible polymers by optical microscopy, DSC and light scattering. Unmixing was induced by different courses of solvent evaporation and by thermal agitation, respectively. Blends comprising different kinds of flexible and rigid chain molecules display various phase patterns in the late stage of phase decomposition which can be characterized roughly as being either regularly bicontinuous or irregularly shaped. Effects of polymer‐polymer interaction and the blending ratio are discussed. Generally, evolution of morphologies depends on both internal parameters of the system and externally imposed unmixing conditions. Limits of percolating morphologies in the course of phase separation can be established qualitativ

ISSN:0258-0322    

DOI:10.1002/masy.19920580109

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe solution structure of flexible chain polymers is described in terms of an equivalent entanglement network characterized by its apparent chain element A'. Such networks can exhibit free penetration of polymer segments, hindered penetration or no penetration at all. The segment interaction effects a hindrance to penetration. It can be characterized by the concentration dependence of the mass of network strand Meresp. the entanglement density ν. Another parameter is the entanglement fraction ß, which describes the ratio of the entanglements actually formed to that possible in case of free penetration. Experimental results with different polymers illustrate these idea

ISSN:0258-0322    

DOI:10.1002/masy.19920580110

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractFor a series of poly(thiocarbonates) derived from bisphenol A several conformational and thermodynamic solution properties (partial specific volume, refractive index increment, effective dipole moment and characteristic ratio) were summarized. The effect of the structure, size and polarity of the different poly(thiocarbonates) side chains on these properties were analyzed. The high rotational freedom of the poly(thiocarbonate) chains, obtained from theoretical calculations, justifies the variation of the different properties experimentally obtained in the studied polymers.

ISSN:0258-0322    

DOI:10.1002/masy.19920580111

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractUsing a renormalized form of the Random Phase Approximation (or Tree Graph Approximation) we analysed data on the zero angle scattering intensity and the apparent radius of gyration for the system polystyrene‐poly(methyl methacrylate)‐bromobenzene. Since the microscopic parameters of this system are known from the analysis of the zero‐angle scattering data, the theory yields a parameterfree prediction of the apparent radius of gyration which fits the data very well. To show the influence of renormalization we also analyse the data by an unrenormalized version o

ISSN:0258-0322    

DOI:10.1002/masy.19920580112

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY