QUANTIFICATION OF STACKING FAULTS IN SYNDIOTACTIC POLYSTYRENE SINGLE CRYSTALS. Masatoshi Tosaka, Noritaka Hamada, Masaki Tsuji, Masahiro Fujita, Shinzo Kohjiya, Institute for Chemical Research, Kyoto University
Syndiotactic polystyrene (sPS) crystals have a unique character; i.e., they have inherent stacking faults in beta-form single crystals (orthorhombic P21P21P21, a=2.87nm, b=0.88nm, c(chain axis)= 0.51nm)[1]. In this study, we tried to determine the proportion of these faults from electron diffraction (ED) patterns and to investigate the dependence of the proportion on crystallization and annealing temperatures. The reliability of estimated values was examined by comparison with the directly counted number of these faults recorded in high-resolution TEM images. Existence of stacking faults is readily deduced from ED patterns of sPS single crystals. They are characterized by certain hk0 (h+k=odd) reflections streaked in the a*-direction; while the other reflections (h+k=even) are spot-like. From the analysis of these patterns, we have already proposed a model for the faults; the faults are defined as successive (irregular) sequence in the regularly alternating sequence of two motifs, each of which is made up of two molecular layers spread along the b-direction [1]. Based on the model, the proportion of the fault can be determined by converting the half-breadth of streaked hk0 reflections. Before the conversion, a component due to instrumental broadening was subtracted from the breadth, assuming that their profiles are Gaussian and instrumental broadening is reproduced on spot-like reflections.
The estimated proportion showed a maximum at 165deg.C. Then, single crystals grown at this temperature, which are to have a maximum proportion of the faults, were annealed for one hour at various temperatures. The proportion of the faults decreased with annealing temperature, but annealed crystals still had more faults than those crystallized at the same temperatures. In the assumed model, these faults can be cancelled only when they move in the a-direction until they reach to a crystal edge or when two faults collide with each other. Thus the small decrease of the proportion by annealing suggests rather small mobility of these faults.
[1] Tsuji et al., MSA Bulletin, 23, 57(1993).