STRUCTURAL STUDY ON SYNDIOTACTIC POLYSTYRENE .4. FORMATION AND CRYSTAL-STRUCTURE OF MOLECULAR-COMPOUND WITH IODINE

Syndiotactic polystyrene was found to form a molecular compound with iodine as well as with a variety of organic compounds. The iodine molecular compound with uniaxial orientation was obtained by immersing amorphous polystyrene (obtained by quenching the melt into ice-water followed by stretching) into molten iodine at 120-130-degrees-C. The crystal structure of the iodine molecular compound is isomorphous to that of the molecular compound with toluene. The crystal data are as follows: monoclinic, space group P2(1)/a, a = 17.29, b = 12.85, c (chain axis) = 7.79 angstrom, gamma = 120.3-degrees (c-unique), and there are eight monomer units (two chains) in the unit cell. The polymer chains take a (-TTGG-)2 twofold helical structure and it is expected, from the viewpoint of the crystal symmetry and the size of the hole, that two iodine molecules occupy one isolated hole formed between the polymer chains. However, in spite of several attempts to prepare the molecular compound, not all the holes contained iodine. The sample used for X-ray structure analysis was estimated to contain about 70% of the expected iodine content. On annealing in the range 130-150-degrees-C, the X-ray reflection intensities changed, indicating escape of iodine to some extent. However, the pure helical form free from the guest molecule was not obtained, in contrast to the case of molecular compounds with organic compounds; on annealing at temperatures higher than 160-degrees-C the iodine molecular compound was directly transformed to the planar form I.