Optical Anisotropy of the Polycarbonate of Diphenylolpropane

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The mean-squared optical anisotropy 〈γ2〉 = (3/2)〈tr (α̑α̑)〉 and the dipolar contribution 〈μTα̑μ〉 to the electric birefringence are calculated for the random-coiled polycarbonate (PC) chain from its molecular geometry, the dipole moment μC for the carbonate group, and the anisotropic polarizability tensors α̑C and α̑ph for the carbonate and phenylene groups, respectively, as determined from experiments on model analogues reported in the preceding paper. Averaging over conformations is performed on the basis of calculated torsional potentials affecting rotations about Cph-O and Cph-C bonds linking phenylene with carbonate and with isopropylidene groups. The averaged invariant 〈tr(α̑χ̑)〉 that determines the magnetic birefringence is similarly evaluated from α̑ and the anisotropy tensors χ̑ for the diamagnetic susceptibilities of constituent groups. Our depolarized Rayleigh scattering and electric birefringence measurements on PC yield results in good agreement with calculations. The calculated Cotton-Mouton constant is about 30% lower than the value deduced from the magnetic birefringence measurements of Champion et al. Apart from this unexplained discrepancy, experiments support the postulated additivity of group polarizabilities and, consequently, recommend optical anisotropy as an index of conformation and structure. © 1982, American Chemical Society. All rights reserved.