STUDIES OF THE SOLID-STATE CONFORMATION OF POLYSILAETHYLENE - AN ORGANIC INORGANIC HYBRID POLYMER WITH AN ALTERNATING C/SI BACKBONE/

Polysilaethylene ([SiH2CH2](n)) (PSE) and deuterated polysilaethylene ([SiD2CH2](n)) have been examined by both vibrational spectroscopy and X-ray diffraction methods above and below the crystallization/melting transition at -20 degrees C, The results confirm previous indications that PSE crystallizes in an all-trans conformation analogous to that found for its all-carbon analog, polyethylene. Raman spectroscopy reve als the appearance of a sharp band at 706 cm(-1) attributable to the s ymmetric Si-C stretching vibration when PSE is cooled below 0 degrees C, while wide-angle X-ray diffraction shows the existence of a crystal line form with a monoclinic unit cell (alpha = 5.70 Angstrom, b = 8.75 Angstrom, c = 3.25 Angstrom; gamma = 97.5 degrees) whose dimensions c ompare closely to the calculated repeat distance using the planar zigz ag conformation of PSE. The calculation of the IR spectra by ab initio methods (Hartree-Fock level of theory) using the 3-21G and 6-31G'' b asis sets agrees well with the experimental IR results. Through the us e of the calculated IR spectra, symmetry analysis, and spectroscopic d ata on the deuterated sample, the assignments of the different PSE vib rational bands have been achieved.