摘要:

AbstractThe original Flory corresponding‐states theory of polymer solutions requires an entropic correction parameterQ12, the sign and value of which seem to be arbitrary, and the physical meaning of which is obscure. Moreover, calculated excess volumes of mixing for many polymer solutions are often in significant disagreement with experimental data. In order to eliminate these problems, we have modified the kinetic part of the partition function, introduced an effective mass for the mixture segment, and adopted the nonlinearity of the number of degrees of freedom with respect to the composition for the mixture segment. In addition, the effect of nonrandom configurations of the segments in the mixture has been included. In the improved equations, derived in this work, the Flory interaction parameter χ can be considered to comprise three parts: (a) a kinetic part due to the contribution of the average number of degrees of freedom and the effective mass of the mixture; (b) a free volume part; and (c) an interaction part including the contributions due to the contact interaction and the nonrandom configuration of the segments in the mixture, caused by the interaction. The improved theory is in good agreement with literature data on polystyrene solutions and poly (dimethyl siloxane) solutio

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290102

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractSorption and permeation of CO2in various annealed polyimide (PI) films were investigated. Dual‐mode sorption and partial immobilization models were used to analyze the data. Sorption of CO2in PI film quenched from above the glass transition temperature (Tg) is greater than in film as received. In fact, sorption is decreased over the entire pressure range by cooling the film slowly. These changes in sorption of CO2can be attributed to a change in the Langmuir sorption capacityC′Hby annealing, since the other dual‐mode sorption parameters,kDandb, are almost independent of annealing. The value ofC′His increased by quenching, and decreased by slow cooling from aboveTg. The two diffusion coefficientsDDandDHaccording to the Henry and Langmuir modes, respectively, for CO2also depend markedly on annealing. Diffusion coefficients of quenched PI films are increased and those of film cooled slowly are decreased compared with values for PI film as received. The change inDHis larger than that inDD. The permeability coefficient of quenched PI films at 100 cmHgis about 1.7 times that of PI film as received. The film structure formed by quenching can enhance permsele

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290103

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe evolution of the viscoelastic behavior of an epoxy resin at various stages of curing has been followed with the changes in the retardation spectrum. The creepJ(t)and recoverable creep complianceJr(t)curves of the neat epoxy resin Epon l00lF (Shell) were determined at temperatures between 30 and 77°C. The viscosity decreased over 8 orders of magnitude as the temperature was increased. Specimens with eight stages of network development were prepared by reacting all of the epoxy resin's oxirane rings with amine hydrogens from varying ratios of a monofunctional amine (methyl aniline) and a tetrafunctional amine 4,4′‐diamino diphenyl sulfone (DDS). Preparations in which 25, 35, and 40% DDS were used did not result in a molecular network, so they were viscoelastic liquids. With 45% DDS, the product had a nascent network and was judged to be just beyond the point of incipient gelation. The remaining preparations from 0.50, 0.60, 0.70, and 1.0 DDS yielded tighter less compliant molecular networks. The creep and recoverable compliance curves were measured over a range of temperatures above the glass transition temperature,Tg. They were reduced toTg, and retardation spectraL(ln τ) were calcu

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290104

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA new method for recording multiple dark‐field transmission electron micrographs using a scanning transmission electron microscope fitted with a quadrant detector is described. Simultaneous multiple recording is particularly advantageous when studying electron beamsensitive polymers and images of crystals of poly(butylene terephthalate) are presented by way of example. Resolution levels of ca. 10 nm are demonstrate

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290105

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractResults for four different volume‐dependent rate processes of an epoxy resin, Epon 1001F, fully cured with a stoichiometric amount of 4,4′‐diamino diphenyl sulfone are presented: (1) specific volume measurements at constant rates of cooling; (2) time‐dependent volume measurements after rapid temperature changes; (3) elongational creep compliance measurements; and (4) shear creep compliance measurements. Voluminal and shear retardation spectra are compared as are the temperature time scale shift factors,aTobtained from the four processes. Volume–temperature cooling curves show the decreasing glass temperature with decreasing rate of cooling, but appear to reach the glass line at a constant temperature regardless of the rate of cooling. This narrowing of the “transition range” is not predicted by the Kovacs, Aklonis, Hutchinson, and Ramos (KAHR) multiparameter model, which assumes thermorheologic

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290106

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractLineshape simulation of13C nuclear magnetic resonances was employed to characterize the structural development of poly (ethylene terephthalate) (PET) during fiber formation and subsequent processing. In all spectra the carbonyl (CA) and glycoethylene (GE) resonances can be simulated with two components. The intensity variation of these components has been interpreted quantitatively on the basis of four morphological components in the solid‐state structure, with clearly defined differences in order between them. The four components are, in decreasing structural order, (i) crystalline (C), (ii) noncrystalline with order in both CA and GE environments (NC1), (iii) noncrystalline with order only in the GE environment (NC2), and (iv) amorphous (NCA). The crystalline component has been taken here to correspond to the high‐density component which has been estimated from flotation and optical density measurements. Such an analysis reveals a smooth pattern of evolution of order within a range of conditions in melt spinning and subsequent thermomechanical processing of PET fibers. Cold drawing at room temperature was seen to induce substantial ordering only in the GE environment. In contrast, annealing at a temperature significantly above glass transition temperature (Tg) for 2 h appears to cause the conversion of amorphous component to crystalline from with little accumulation of the intermediate compone

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290107

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractHigh‐resolution13Carbon nuclear magnetic resonance (NMR) spectra of Nylons 4, 6, and 66 in the solid state were measured over a wide range of temperature. From the results, it was found that resonance lines of crystalline and noncrystalline components were separable and their chemical shifts were determined. The13C chemical shift behavior is closely related to their conformation. The origin of the conformational effects on the chemical shifts is discusse

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290108

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractEthylene‐vinyl alcohol copolymers from 0 to 57 mol % of vinyl alcohol were investigated for potential contact lens surface modification. Films of the ethylene‐vinyl alcohol copolymers made by solution casting, showed that the copolymers with a high percentage of vinyl alcohol groups possessed excellent surface properties such as good wettability, low protein (albumin) and lipid adsorption, and no conformational change of the adsorbed protein. Utilizing the Langmuir‐Blodgett dipping technique, an ultrathin layer of ethylene‐vinyl alcohol copolymer was deposited on a silicone rubber substrate. This initial results confirm that wettability was improved and the amount of protein adsorbed was reduced significantly after only one depositi

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290109

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of segmented polyurea urethane and polyurea block copolymers based on a hexane diisocyanate (HDI) modified aminopropyl terminated polydimethylsiloxane soft segment was synthesized. The hard segments consisted of 4,4′‐methylene diphenylene diisocyanate (MDI) which was chain extended with 1,4‐butanediol (BD),N‐methyldiethanolamine (MDEA), or ethylene diamine. Zwitterionomers were prepared by quaternizing the tertiary amine of the MDEA extended material with γ‐propane sultone. The effect of chemical structure on the extent of phase separation and physical properties was studied using a variety of techniques including thermal analysis, dynamic mechanical spectroscopy, tensile testing, and small‐angle x‐ray scattering. It was observed that the compatibility between the nonpolar polydimethylsiloxane soft segments and the polar urethane hard segments was improved by inserting HDI linkages into the polydimethylsiloxane soft segments. The aggregation of hard segments was enhanced by increasing hard‐segment content or by the introduction of ionic functionality. The tensile strength and modulus of these materials was higher than those of polyurethanes containing soft segments based on polydimethylsiloxane and

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290110

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe solubility of water vapor in four different polyimides at 100% relative humidity and 22°C was measured by means of a quartz crystal microbalance system. The results confirm earlier conclusions that diffusion in these polymers is Fickian, and are sufficiently precise that the order of solubilities is unambiguous. The differences between the values are interpreted in terms of morphological variations rather than variations in chemical affinity for water. Diffusion coefficients are also reported

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290111

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY