Crystal-Structure of the Alpha-Form of Syndiotactic Polystyrene

Models for chain packing for ordered and disordered modifications of the alpha-form of syndiotactic polystyrene are suggested, through quantitative comparisons between X-ray diffraction intensities and calculated structure factors. According to the reported analysis, zig-zag planar chains are packed in the hexagonal unit cell proposed by Greis et al., but with different orientation and relative height of the phenyl groups. In particular, the phenyl groups in both ordered and disordered modifications are packed according to rhombohedral symmetry. The disorder in the alpha' modifications correspond to the statistical occurrence o two different, nearly isosteric, orientations of triplets of chains at well defined locations of a threedimensional lattice, which generate a rhombohedral symmetry for the whole unit cell.