摘要:

AbstractA study has been made of the mechanical, thermal, and morpholigical characteristics of melt‐crystallized isotactic polypropylene containing high levels of the β or pseudohexagonal crystalline form. Different levels of β‐form crystallinity were produced in the polymer by blending in low levels of quinacridone dye nucleating agent. Microscopical studies of the crystallization process revealed that both α‐form (monoclinic), and β‐form spherulites nucleated on the dye particles, with α‐spherulite growth commencing at a higher temperature. These observations were able to qualitatively explain the dependence of β‐form level on both the nucleant concentration and its state of dispersion in the polymer. Improving the dispersion of the nucleant was found to reduce the level of β‐form crystallinity if the nucleant concentration exceeded an optimum level. A new procedure for quantifying the volume fraction of β spherulites in a sample was developed which utilized the technique of selective solvent extraction. From volume‐fraction, x‐ray, and density data, the pure α and β crystal densities were obtained. Dynamic mechanical measurements‐obtained on unoriented specimens containing varying levels of β‐form crystallinity showed an increase in the magnitude of the damping in the post‐Tgregion with increasing β content. High levels of the β form lead to lower values of the modulus and yield stress, and higher values of the elo

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240301

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe self‐diffusion coefficient of chloroform in poly(isopropyl acrylate)—chloroform solutions has been studied as a function of concentration and temperature by using the pulsed‐field‐gradient spin‐echo NMR method. It is found that the self‐diffusion coefficient of the solvent can be adequately fitted by using a simple free‐volume approach with either a concentration or temperature superposition. It was noted that the free‐volume parameters derived from the self‐diffusion data are the same as those derived from deuterium NMR transverse relaxation‐time measurements of the polymer in the same system. The equality of these two sets of experiments suggests a fundamental relationship between the two different processes. The simplest explanation is that the free volume necessary for the local segmental motion of the polymer and the translation of the

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240302

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractDiffusion coefficients of Cu2+in the form of its carboxylate have been measured in isotactic polypropylene as a function of temperature (90–128°C) and extent of preoxidation. Diffusion take place from the metal catalyst/polymer interface into the bulk polymer. The diffusion is dependent on the extent of preoxidation and temperature but not on the type of catalyst (Cu, CuO, CuO0.67). Analysis of polymer sections for Cu2+ions was carried out with a selective Cu2+electrode. Diffusion in isotactic polypropylene is about 1000 times faster than in lowdensity polyethylene. The carboxylate anion appears to have about 7 C‐atoms for diffusion in isotactic polypropylene compared with 29 C‐atoms for low‐density poly

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240303

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractWe synthesize a quantitative theory for the radius of gyration, second virial coefficient, intrinsic viscosity, and friction coefficient for polyelectroytes in dilute solution from existing treatments of electrostatic and hydrodynamic interactions within and among wormlike chains. Comparison with data for K‐PSS demonstrates the importance of accounting for nonlinearities in the electrostatics and the finite diameter of the polymer backbon

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240304

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractHigh‐pressure sorption (up to 50 atm) for CO2, N2, and Ar in poly(vinyl benzoate) (PVB) was studied at temperatures from 25 to 70°C by a gravimetric method utilizing an electromicrobalance. The results are described by Henry's law above the glass transition temperatureTgfor all gases. The dual‐mode sorption model, Henry's law plus a Langmuir isotherm, applies to the sorption isotherms of N2and Ar in the glassy state, and the dual‐mode parameters are given. For CO2, a new type of sorption isotherm is observed belowTg. The isotherm is concave to the pressure axis in the low‐pressure region and turns into a straight line with increasing CO2pressure which can be extrapolated back to the coordinate origin. The linear part of the isotherm is characteristic of the rubbery state, while the nonlinear part stems from glassystate behavior. The “glass transition solubility” of CO2, at which PVB film changes from the glassy to the rubbery state, decrease as the temperature increases. The disappearance of microvoids, that is, the decrease of the Langmuir capacity, may be due to a large plasticizing effect of sorbed CO2. The difference between the N2and Ar isotherms and the CO2isotherm is discussed from thi

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240305

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractAnalysis of the increase in the width of the seven meridional (OkO) reflections of the γ form of nylon 6 suggests microstrain rather than paracrystallinity as the source of lattice disorder along the chain axis. It is shown that the intensity of the (020) reflection depends not only on the amount of γ phase present in the fiber, but is also influenced by orientation, Lorentz factor, and crystallite size. Calculations confirm the presence of a weak, diffuse meridional band at 2θ=6° (Cu Kα) when the coherence length along the chain axis corresponds to less than two unit c

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240306

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe sorption of gases in polymers below their glass‐transition temperatureTgis known in many cases to be described by the “dual sorption” theory, according to which the gas is held in accordance with both the Langmuir and Henry's laws. Based on this theory, expressions for the “effective diffusion coefficient” in the glassy polymers have been obtained by investigators in the past, notably by Paul and Koros.2The present analysis regards the glassy polymers as inhomogeneous with regions on which the gas sorption follows the Langmuir law. Assuming that the linear dimensions of these regions, which are often referred to as “microvoids” (although they are not space filled by vacuum), are small compared to the macroscopic length of interest but large compared to the mean free path of the penetrant gas molecules, we derive a rigorous relation between the average flux and the concentration gradient in the polymer and show that this relation can be expressed in terms of an “effective diffusion coefficient”Deffwhich depends on the details of the microstructure, i.e., the size, shape and spatial distribution of the “microvoids.” This expression forDeffis shown to reduce to that of Paul and Koros2in two situations: (1) when the “voids” consist of slabs running parallel to the concentration gradient, and (2) when the “voids” are spherical and the temperature of the polymer is not too different fromTg. The results of the present study lead to an alternative procedure for interpreting the experimental data on sorption and permeation which may have some advantages over the procedure currently employed. Finally, the analysis presented here is also applicable to polymers

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240307

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThermal analysis is used to elucidate the fusion of fractions of poly(ethylene oxide) of from 3500 to 5000000 molecular weight. In addition, the equilibrium and nonequilibrium phase diagrams of binary mixtures of these fractions have been studied. Complete segregation from high‐molecular‐weight polymer is possible up to at leat 20000 molecular weight. This segregation is not governed by the melting/crystallization equilibrium, but rather by molecular nucleation. Over a broader crystallization temperature range three regions can be identified. At low crystallization temperature, solid solutions result, at higher temperature one finds an intermediate type of crystallization, and ultimately one reaches complete, eutectic segregation. This work will be followed by analysis of the kinetics of crystallizat

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240308

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA kinetic study of crystallization of fractions of poly(ethylene oxide)s between 3500 and 5,000,000 MW and their mixtures from the melt by differential scanning calorimetry and optical microscopy is reported. For the fractions the crystal growth rate is inversely dependent on the logarithmic molecular weight. Binary mixtures of widely different molecular weights show mixed‐crystal formation at low crystallization temperature described by a single Avrami equation with exponent 3. At higher temperature, increasing segregation takes place despite higher deposition probabilities of the low molecular weight. Two consecutive Avrami equations describe the crystallization. Before the equilibrium melting temperature of the low molecular weight component is reached, complete segregation occurs. This segregation is possible up to at least 20,000 MW. Classical crystallization theory is unable to describe the process. Molecular nucleation seems a viable alternative for the description of crystallization of both fractions and mixtures. Reversibility of crystallization is on a one‐molecule scale and reaches thermodynamic reversibility as the molecular length approaches monomer s

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240309

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA coupling model of relaxation that can account for viscoelastic properties in both the softening and terminal dispersions is found to explain quantitatively also their different temperature dependences.

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240310

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY