OPTICAL ANISOTROPY AS AN INDEX OF POLYMER MICROSTRUCTURE IN POLY(PHENYLMETHYLSILOXANE) CHAINS

Absolute depolarized intensity RVH for newly synthesized poly(phenylmethylsiloxane) (PPMS) chains with different stereochemical structure has been obtained from the low-frequency depolarized Ray-leigh spectra of dilute PPMS solutions in CC14 at 25 °C. The effective optical anisotropy (γ2)/x of PPMS with degree of polymerization x ≈ 160 was found to be insensitive to refractive index variation with different solvents. The measured optical anisotropy of the monomer (γ2) and polymer were compared with computed values based on the rotational isomeric state theory. In the latter, geometry of the chain, conformational energies, and group anisotropies were obtained from the analysis of the experimental molar Kerr constantmK and optical configuration parameter Δα for atactic PPMS. The theoretical calculation of (γ2)/X yields a good qualitative account of its main feature, i.e., insensitivity to x (for x > 60) and variation with chain tacticity. The theoretical value, however, exceeds the experimental (γ2)/x while agreement is achieved with the experimentalmK and Δα. Better approximation of γ2 and (γ2)/x requires modification of the conformational energies and a lower value for the group anisotropy Δαsiph, whose magnitude is quite uncertain. Possible explanations for this discrepancy are discussed herein. © 1990, American Chemical Society. All rights reserved.