Depolarized Rayleigh spectra of siloxane polymers

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Abstract
We report measurements of depolarized Rayleigh spectra IVH(ω) of polyphenylmethyl siloxane (polymer A) in bulk and in carbon tetrachloride, of polydimethylphenylmethyl siloxane (copolymer B) in bulk, and of depolarized Rayleigh intensity IVH of polydiphenyl siloxane in carbon tetrachloride. From the temperature dependence and the concentration dependence of IVH, we were able to determine positive intermolecular and intramolecular static pair correlations of polymer A and of copolymer B, and negative intermolecular and intramolecular static pair correlation of polydiphenyl siloxane solutions. The results are explained in terms of the most preferred orientation of phenyl groups attached to the polymer backbone. The linewidths of depolarized Rayleigh spectra of polymer A and of copolymer B can be attributed as due to the crankshaft type of motion of the polymer backbone which orients the polarizability anisotropy of the phenyl groups. The local reorientation time is virtually independent of the macroscopic viscosity. The apparent activation energy (∼2.3 kcal/mol) is much lower than that determined by the dielectric relaxation technique but is of the same order as that calculated from Brillouin spectra.