Kinetics of the formation and orientation of domain structure in amorphous polymers

Abstract

Abstract The method of small-angle x-ray scattering (SAXS) has been used to investigate the structure of amorphous flexible-chain polymers: poly(vinyl acetate) (PVA), polystyrene (PS), and poly(methyl methacrylate) (PMMA) at temperatures slightly lower (by 10–15°C) than the glass transition temperature (Tg) under conditions close to the equilibrium state. A state of thermodynamic equilibrium was attained by annealing in this temperature range for a long time. After stretching by 5–20%, the samples subjected to prolonged annealing exhibited a supermolecular structure of the domain type which was uniquely determined from the appearance of the small-angle discrete scattering on the equator of the pattern with respect to the stretching axis. The pattern assumes a characteristic crossline appearance: an intense diffuse scattering of rhombic shape along the stretching axis and the discrete scattering normal to it on the background of a narrow diffuse scattering. The domain structure can be observed only in the range below Tg. Conditions of the appearance of discrete scattering and its dependence on the draw ratio and the stretching rate were investigated, and the size of the domains, their amount, and thermodynamic properties were evaluated. The observed structure is interpreted in terms of the appearance of the nematic mesophase.