A light-scattering study of 1-4 cis-trans polybutadiene

Light-scattering measurements on 1-4 polybutadiene of two molecular weights have been carried out using two different tandem Fabry-Perot interferometers in the back-scattering and 90 degrees scattering geometries. The Raylejgh-Brillouin spectrum has been measured at different temperatures through the glass transition. Relaxation times and sound velocities have been fined to a hydrodynamic formula, with as few independent parameters as possible. Comparison with previous measurements shows that the Brillouin relaxation times do not follow the structural or alpha relaxation. Forcing the fit either with the times of the alpha process or with a high-frequency relaxation channel does not yield satisfactory results. The only processes arising on a similar timescale and with comparable activation energies are intra-chain conformational changes rates as computed by molecular dynamics. A possible mechanism linking these conformational changes to the damping of the Brillouin lines is suggested.