STRUCTURAL STUDY ON SYNDIOTACTIC POLYSTYRENE .3. CRYSTAL-STRUCTURE OFPLANAR FORM-I

The crystal structure of a planar zigzag form of syndiotactic polystyr ene (planar form I) obtained by annealing as-cast samples from solutio ns (molecular compounds with the solvents) was studied by X-rays. Crys tal data are as follows: orthorhombic system, space group P2(1)2(1)2(1 ) (no. 19), but finally Pbnm (no. 62), a = 8.81 angstrom, b = 28.82 an gstrom, c(chain axis) = 5.06 angstrom, eight monomer units (four chain s) per unit cell. Planar form I is different in alignment of the plana r zigzag chains from planar form II obtained by melt-crystallization, which belongs to the hexagonal system. Moreover, the crystal structure of planar form I is characterized by a 'stacking fault' in the molecu lar packing.