Conformation of poly(dimethyl siloxane) and polystyrene in solution measured by polarized Raman scattering

Depolarization ratios ρ have been measured over ranges of temperature T and molecular weight M for polystyrene (PS) dissolved in cyclohexane (1002 cm−1 Raman band) and for poly(dimethyl siloxane) (PDMS) dissolved in benzene (2907 cm−1 Raman band). The ranges in the case of PS are 15 < T < 65°C and 2 × 103 < M < 4 × 105 and in the case of PDMS are −3 < T < 60°C and M = 104. Measurements were also made of PDMS radii of gyration using conventional light scattering. The results are interpreted in terms of a theory connecting rotational isomeric populations with polymer extension. In the case of PDMS, an experimental value of the proportionality constant for trans isomers (D2 = −3.9 ± 0.9) is deduced. This is closer to the theoretical value than previous estimates but there is still some discrepancy. In the case of PS the isomeric changes resulting from extension are independent of M for M > 104. Deviations are observed for lower M.