摘要:

AbstractIn order to gain insight into the viscosity behavior of linear block copolymers, formulas have been developed for the calculation of radii of gyration of block copolymers whose blocks deviate from the theta condition by any given degree. In the course of this study the radii of gyration of sets of centrosymmetric arrays have been studied and the mean separation between the center of mass and the end of a random chain has been calculated. The results show that for AB block copolymers of fixed degree of polymerization (DP), the intrinsic viscosity varies in a monotonic, sigmoidal fashion when the composition is varied from homopolymer A to homopolymer B. The magnitude of the effect depends upon the relative stiffness of the A and B segments and upon the total DP. In ABA copolymers, on the other hand, at constant DP, varying the composition from all A to all B usually leads to a composition‐intrinsic viscosity relationship containing maxima and minima. As A becomes increasingly stiff compared to B, this relationship tends towards a monotonic one. This behavior is surprising and should be checked experimentall

ISSN:0360-8905    

DOI:10.1002/polc.5070630105

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

年代:1978

数据来源: WILEY

摘要:

AbstractPhase transformations associated with spinoidal decompositions are reviewed. Such phenomena associated with inorganic glasses are considered for the case of amorphous binary systems of organic high polymers. The thermodynamic and experimental considerations are projected and sample systems selected and tested. Results are presented for poly 1, 4(2, 6 dimethylphenylene oxide) plus a copolymer of styrene and orthochlorostyrene and also for this plasticized binary system.

ISSN:0360-8905    

DOI:10.1002/polc.5070630106

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

年代:1978

数据来源: WILEY

摘要:

AbstractDiffusional processes in polymer blends, although important in determining the characteristics of the blend, are poorly understood. Virtually no data are available in the open literature. A novel experimental technique useful in the study of diffusion in compatible polymer/polymer systems is presented. It uses a scanning electron microscope and dispersive energy analysis of the x‐ray fluorescence profile in the interdiffusion of two polymer components. The technique is used to determine the diffusivity in a poly(vinyl chloride)‐poly(±‐caprolactone) at 70°C. The diffusion coefficient [D= (1.59 ± .13) × 10−12cm2/sec] is of the same order as the only reported polymer/ polymer diffusion m

ISSN:0360-8905    

DOI:10.1002/polc.5070630107

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe morphology of blends of poly(ϵ‐caprolactone) (PCL) with poly(vinyl chloride) (PVC) was investigated. The observations made with the optical microscope and electron microscopes indicate that for the blends rich in PCL, the samples are almost completely filled with spherulites composed of lamellas radiating from the spherulite center and twisting regularly. As the concentration of PVC increases, the texture of the spherulites becomes increasingly coarse and open. The results of the elementary analysis, made with an x‐ray spectrometer, indicate a uniform distribution of chlorine atoms in the blends regardless of the composition. X‐Ray diffraction studies reveal that the unit cell dimensions of PCL are not changed by the presence of PVC. It is believed that the PVC molecules were trapped within the spherulites and rejected preferentially into interlamellar regions. The results of differential scanning calorimetry measurement show that the crystallinity of PCL decreases with increasing PVC content. PCL in the blend containing more than 70% PVC exhibits no tendency to crystallize. The blends show a depression of the melting point of PCL. Over a wide range of composition, the blends display a single glass transition intermediate between the transition of the respective components. The glass transition shows a systematic increase with PVC concent

ISSN:0360-8905    

DOI:10.1002/polc.5070630108

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

年代:1978

数据来源: WILEY

摘要:

AbstractCrystallization kinetics of poly(e‐caprolactone) from the blends of poly(e‐caprolactone (PCL) and poly(vinyl chloride) (PVC) were investigated. The isothermal spherulitic growth rates were measured with an optical microscope. Linear growth rates were obtained for all samples at temperatures between 20° and 35°C. The introduction of PVC into PCL resulted in a reduction in spherulitic growth rate. The overall crystallization rates were measured with a density gradient column. The Avrami equation was employed to analyze the isothermal crystallization kinetics. It was found that the value of Avrami constantkdecreases markedly with increasing PVC concentration. However, the Avrami constantnhas a value in the neighborhood of 3, almost independent of the composition. In light of these results, it is suggested that, for these blends, the crystallization proceeds by heterogeneous nucleation, followed by a three‐dimensional

ISSN:0360-8905    

DOI:10.1002/polc.5070630109

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe effect of shear on polymer crystallization kinetics has been studied for three materials at several shear rates and degrees of supercooling. Two poly(ethylene oxide) samples, with molecular weights of 72, 200 and 12, 600, and a poly(e‐caprolactone) material, with a molecular weight of 9, 400, were investigated. The apparatus used was a concentric cylinder viscometer, which also functions as a dilatometer, capable of detecting very small volume changes on crystallization. The shear‐rate range of the experiments was 0 to 60 sec−1. Avrami kinetics were used to describe the transformation process and the exponent was found to increase from the quiescent value of 3 to a value greater than 5 with increasing shear rate for all materials studied. The acceleration in the transformation process was associated with a reduction in induction time. The value of induction time at high shear rates did not significantly decrease with increasing shear rate, indicating a saturation effect with shear. This was most pronounced in the low molecular weight samples. The value of induction time for the high molecular weight poly(ethylene oxide) sample, under identical experimental conditions, was substantially less than that of the low molecular weight material in all cases. Nuclei formation measurements were made for the crystallizing melt in a separate instrument. Nuclei formation under shear was very different from quiescent behavior and increased substantially with increasing shear rate. These experimental observations lead to the conclusion that accelerated crystallization is due to increased molecular chain extension and orientation under shear. This orientation greatly enhances the nucleation process, which is thought to be the rate controlling step in the crystalline transformation. This enhancement results in shorter induction times and more rapid crystalliz

ISSN:0360-8905    

DOI:10.1002/polc.5070630110

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe performance of a differential scanning dilatometer is described in terms of the volume changes recorded near the isotropic to cholesteric transition for cholesteryl laurate. The instrument is also applied to a study of crystallization kinetics. The isotropic–nematic phase transition inp‐azoxyanisole was also examined by optical microscopy. An instability in the phase boundary is observed at increasing transformation rates. Size effects on this transition are investigated by absorbing the sample in porous silica. The transition is depressed 0.3°K in a 300 Å diameter

ISSN:0360-8905    

DOI:10.1002/polc.5070630111

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe entropy correlation theory predicts that any structural change whichdecreasesthe configurational entropyScof a complex molecular system will lead to an approximately equalincreasein the activation entropy ΔS*for structurally controlled rate processes such as diffusion. In symbols, Δ(ΔS*) =‐ΔScor ΔS*(A) = ΔS*(1)‐ΔSc, where, in the present case, the ordering parameter A is the elongation ratioL/L0. Although the theory is believed to be of wider scope, this paper deals with its confirmation for the case of gas diffusion in permanently stretched polymeric membranes. The systems investigated included representative poly(alkyl methacrylates) (viz. methyl, ethyl, isobutyl, and normal butyl methacrylate and a copolymer), and a selection of nonpolar and polar gases (Ar, O2, N2, CO). Diffusion and permeation measurements on the oriented films were made by the Daynes‐Barrer time lag method using a mass spectrometer for the detection instrument. The degree of orientation and its stability during an experiment were characterized by measurements of optical birefringence. For a comparison of the general theory with the specific data, it was found useful to prepare the samples in such a way that ΔSc≈a(A2+ (2/A)–3, corresponding to a quenched elastomer; then the data could be represented such that logDOis a linear function of ΔSc, whereDOis the preexponental factor in the diffusion equati

ISSN:0360-8905    

DOI:10.1002/polc.5070630112

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

年代:1978

数据来源: WILEY

摘要:

AbstractThe current expressions for the molecular size distributions in certain polycondensing systems of linear or branched‐chain polymers were derived by Flory and by Stockmayer in the limit of infinitely large systems. These expressions are experimentally verified in the sol. But the expressions for the distributions of nonlinear polymers, although manifesting the observed gel point, do not describe a gel phase. With a view towards ultimately deriving expressions that do describe the gel, a probabilistic theory of condensation polymerization in finite systems is introduced here. The theory is based on Stockmayer's statistical weight factor, ω, and, as presented, applies to the elementary system composed of chemically identical structural units, each bearing two or more chemically identical functional groups. The probability density function for molecular size distributions is constructed from ω, and expressions for the mean number ofk‐mers and the variance about this mean are derived from it. A generating function formalism for evaluating these expressions exactly is exhibited in the elementary case of linear polymers. Asymptotic expansions of the exact expressions for the means and variances are then obtained in the large system limit. The expansion for the means shows that the Flory‐Stockmayer expression represents the distribution of linear polymers accurately—in finite systems—only at low molecular weights. The expansion for the variances justifies—at low molecular weights—the expectation that observed distributions differ negligibly from the mean distribution, but shows that populations of higher molecular weight polymers deviate markedly f

ISSN:0360-8905    

DOI:10.1002/polc.5070630113

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

年代:1978

数据来源: WILEY

摘要:

AbstractIt has been found that the AB block polymers of polystyrene and poly(dimethylsiloxane) form micelles in normal alkanes. The micelles are swollen by methylene chloride or cyclohexane which gives to an increased turbidity and an increased mobility of the polystyrene. Small–angle x–ray scattering data indicate that the polystyrene decreases in size as methylene chloride or cyclohexane are added. A model is proposed to explain these resu

ISSN:0360-8905    

DOI:10.1002/polc.5070630114

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

年代:1978

数据来源: WILEY