Wiley

The morphology of the ionomer resin from which Nafion perfluorinated membrane products are made was studied with wide‐angle and small‐angle x‐ray diffraction. A reflection observed in the small‐angle x‐ray scan from hydrolyzed polymer is attributed to ionic clustering. The effects of equiv wt, cation form, temperature, water content, and tensile drawing on this reflection were studied and are discussed.

The Raman spectrum of partially crystalline polyethylene can be described as a superposition of three components, which originate from the orthorhombic crystalline phase, a meltlike amorphous phase, and a disordered phase of anisotropic nature, where chains are stretched but have lost their lateral order. The mass fractions involved in the three phases can be derived directly from the integral intensities of characteristic bands without an additional calibration procedure. A comparison of the results obtained for a variety of samples shows agreement with the crystallinities derived from the density, and the small‐angle and wide‐angle x‐ray diagrams. Data indicate that the disordered anisotropic phase is located at a transition zone between crystalline and amorphous layers. Application of the method in a temperature‐dependence experiment permits a detailed examination of partial melting.

Films of chitosan, prepared by different fabrication processes, were examined at several structural levels, from the molecular to the macroscopic. This revealed the presence of polymorphic crystal forms, which varied with film treatment. Similarly, morphological structures varying from spherulites to rods were formed, depending on film processing conditions. The effect of structure on the mechanical properties, as well as the orientability of the films, were also investigated.

A temperature‐dependent small‐angle x‐ray scattering and electron microscopic study on a sample of low‐density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron‐density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the crystallization and melting behavior. The temperature‐dependent changes in this thickness distribution provide a natural explanation for the large reversible changes in long‐spacing.

The α and β relaxations of a variety of polyethylenes have been extensively studied using lowfrequency dynamic mechanical methods. The main focus of this work has been both the control and the quantitative measurement of the key structural factors that describe semicrystalline polymer systems. The structural factors that have been examined in detail include the level of crystallinity, the crystallite thickness, the interfacial content, and the supermolecular structure. Consequently a variety of other types of supplementary measurements were made to accomplish the necessary characterization. The location of the α transition is found to depend primarily on the crystallite thickness. There also is the distinct possibility that the interfacial structure exerts an important influence. The level of crystallinity and the supermolecular structure do not play a significant role in the location of T_α. A strong correlation is found with the carbon‐13 NMR crystalline T₁, which is reported in a separate paper. From analysis of the influence of the different structural factors on the β transition, it is concluded that this transition results from the relaxation of chain units which are located in the interfacial region. The elusiveness of this transition and the contradictory reports that have existed in the literature are given a ready explanation. The enhancement of this transition by branching and copolymerization follows naturally as does its invariance with counit content.

The supramolecular organization of the aromatic polyamide fiber Kevlar 49 has been studied using a combination of electron diffraction and electron microscope dark‐field image techniques. The dark‐field images derived using selected reflections from longitudinal sections exhibit axial banding of two main types having periodicities of 500 and 250 nm. Careful analysis, including tilting experiments, conclusively shows that the supramolecular architecture of these fibers consists of a system of sheets regularly pleated along their long axes and arranged radially.

Infrared spectra in conjunction with calorimetric measurements have been used to follow the crystallization process and microstructural changes of poly(ethylene oxide) (PEO) in poly(ethylene oxide) and poly(methyl methacrylate) (PMMA) blends. We have given particular attention to compositions containing low PEO concentrations. The crystallization behavior and the resultant microstructures of PEO are strongly perturbed by the presence of PMMA. In addition, we found phase separation and trans sequences of PEO to be present, especially at low PEO concentrations.

Hydrostatic pressure usually increases the glass transition temperature T_g of a polymer glass by decreasing its free volume; if the pressurizing environment is soluble in the polymer, however, one might expect an initial decrease in T_g with pressure as the polymer is plasticized by the environment. Just such a minimum in the T_g of polystyrene (PS) is observed as the pressure of CO₂ gas is increased over the range 0.1–105 MPa from both ultrasonic (1 MHz) measurements of Young's modulus E and static measurements of the creep compliance J. A time‐temperature‐pressure superposition law is obeyed by PS which allows a master curve for the compliance to be constructed and shift factors to be determined. A master curve for E is then obtained by using the Boltzmann superposition principle. The compliance J reaches a maximum, and E and T_g reach minima, at a CO₂ pressure of ca. 20 MPa at both 34 and 45°C, which are above the critical temperature (31°C) of CO₂. At the minimum, T_g is 41 at 45°C and 36 at 34°C, the larger depression at 34°C evidently corresponding to the higher solubility of CO₂ at the lower temperature. The plasticization effect due to CO₂ can be isolated by subtracting the effect of hydrostatic pressure alone from the experimental data. The results leave no doubt that at high pressures CO₂ gas is a severe plasticizer for polystyrene.

A model is discussed which explains reported complex effects of feed composition and pressure on component permeabilities in high‐pressure gas separators based on glassy polymer membranes. A special form of Fick's law which accounts for the fact that penetrants in glassy polymers sorb into and diffuse through two different molecular environments provides the basis for the analysis of gas mixture permeation. Potential deviations from the theory are discussed in terms of separable solubility‐and mobility‐related effects.

Doi and Edwards have recently proposed a molecular theory for the dynamics of entangled polymer liquids based on a tube model to represent the mutual constraints on configurational rearrangement of the chains. Expressions for diffusion coefficient, plateau modulus, zero‐shear viscosity, steady‐state recoverable compliance, and terminal relaxation time can be devloped, and relations among these properties that depend only upon observable quantities can be obtained. Several such relations are derived and are compared with experimental observations.