Studies of the crystallization kinetics of natural rubber networks held in simple extension are reported. In these experiments the length of the specimen was held constant, and the crystallization process was followed by the decay in stress that occurred. A wide range of extension ratios and crystallization temperatures was encompassed by these experiments. From an analysis of the shapes of the crystallization isotherms, it can be concluded that major changes take place in the nucleation and growth processes as the extension ratio is increased. This conclusion is in accord with reports in the literature of changes in the crystallite morphology with extension ratio. Analysis of the temperature coefficient of crystallization, by means of nucleation theory, indicates a substantial increase in apparent interfacial free energies with increased deformation. This latter observation is interpreted to indicate a departure from a correlated crystallization process to one where isolated crystallites are formed.

Detailed studies of the fusion of natural rubber, following isothermal crystallization, has revealed a hitherto undetected low temperature transition which depends on the crystallization temperature. This transition is shown to be a melting phenomenon which is not caused by any polymorphic structural changes. It can be attributed to the formation of less stable crystallites which develop as the transition progresses.

For inertial confinement fusion experiments, a copolymer of acrylonitrile and styrene (AS) shell overcoated with a cross-linked polyvinyl alcohol (PVA) has been fabricated in order to obtain good gas-barrier properties and resistance to beta decay of tritium. The fabrication method is based on the emulsion method using the interfacial poly-condensation reaction between water and oil phases. Cross-linked PVA with a thickness of 5 μm has been successfully overcoated on an AS shell. The surface roughness has been estimated using an atomic force microscope to be 0.5 nm (root mean square).

SynopsisSmall-angle x-ray scattering from solid solutions of different molecular weight fractions of partially brominated polystyrene in polystyrene has been studied. The results of this study indicate that polymer chains in bulk have a radius of gyration proportional to the square root of molecular weight, which is consistent with the random coil model. However, these radii are approximately 20% larger than the unperturbed radii deduced by light scattering in dilute solutions.