PHOTON-CORRELATION SPECTROSCOPY OF SYNDIOTACTIC POLY(N-BUTYL METHACRYLATE) NEAR THE GLASS-TRANSITION

Slow relaxing longitudinal density fluctuations in bulk syndiotactic p oly(n-butyl methacrylate) [PBMA] were studied by photon correlation sp ectroscopy as a function of temperature from 70 to 90-degrees-C. The s hape of the light-scattering relaxation function broadened as the temp erature approached the glass transition (T(g) = 55-degrees-C). The ave rage relaxation time shifted with temperature, consistent with previou s studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was cl early bimodal and the shape altered with temperature. The higher frequ ency peak in the distribution corresponds well with previous mechanica l and dielectric relaxation studies of the intramolecular relaxation o f the acrylate ester side chain. The resolution of the distribution in to two modes is due to a well-defined side-chain motion with relaxatio n strength comparable to the primary glass-rubber relaxation. (C) 1994 John Wiley & Sons, Inc.