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We present Rayleigh‐Brillouin light scattering data of highly syndiotactic poly(n‐butyl methacrylate) [PBMA] whose glass transition temperature as measured by DSC is 55°C. The Brillouin peak shifts, Brillouin peak widths, and Landau‐Placzek ratios from −15 to 130°C are reported. The Brillouin peak widths decrease continuously through the glass transition region. This indicates a continual decrease in the strength of processes whose relaxation times are about 10−10 s with decreasing temperature even as the system becomes glassy. The Landau‐Placzek ratio above the glass transition is about 3, indicating the high optical purity of our sample. This low Landau‐Placzek ratio arises from the sample's homogeneous stereochemistry. Some of the anomalous behavior observed around 40–50°C in previous PBMA studies is explained in terms of syndiotactic regions within a largely atactic sample.

Slow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n‐butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light‐scattering relaxation function broadened as the temperature approached the glass transition (Tg = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well‐defined side‐chain motion with relaxation strength comparable to the primary glass‐rubber relaxation. © 1994 John Wiley & Sons, Inc.

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