Optical anisotropy of polystyrene and its low molecular analogues

Abstract

Depolarized Rayleigh scattering (DRS) of benzene, toluene, cumene, and t-butylbenzene, 2,4-diphenylpentane (DPP) 2,4,6-triphenylheptane (TPH), and atactic polystyrenes (PS) with average degrees of polymerization of 21, 38 and 96 have been measured in carbon tetrachloride at λ= 632.8 nm and T= 25°C. The optical anisotropies γ² deduced from the DRS of benzene and toluene are consistent with results obtained by LeFèvre and co-workers from the electric and magnetic birefringence. The anisotropy attributable to the phenyl group is altered markedly by methyl substitution in passing from benzene to toluene. Further substitution on the methyl group has only a minor effect. Optical anisotropies of PS and its oligomers DPP and TPH are calculated from the polarizability tensor for cumene, chosen as the closest analogue of the repeating unit of PS. Values of 〈γ²〉 computed on this basis by averaging over the conformations of meso and racemic DPP, of the mixture of isomers comprising TPH, and of atactic PS are in good agreement with the results of the DRS measurements. 〈γ²〉 for PS calculated as a function of stereochemical constitution decreases from 97 Å⁶ to 30 Å⁶ in passing from syndiotactic to isotactic chains.