Crystal structure of form III of syndiotactic poly(p-methylstyrene)

The crystal structure of form III of syndiotactic poly(p-methylstyrene) is presented. Chains in nearly trans-planar conformation are packed in an orthorhombic unit cell with axes a = 13.36 Å, b = 23.21 Å, and c = 5.12 Å. The crystalline density is 0.988 g/cm3 with four chains in the unit cell (8 monomeric units); space group Pnam. Structure factors and packing energy calculations are shown. A refinement of the structure with the Rietveld method is also presented.