THE DYNAMICS OF POLY(N-BUTYL ACRYLATE) ABOVE THE GLASS-TRANSITION

Measurements of the dielectric constant of poly(n-butyl acrylate) have been taken in the frequency range 100 Hz-3 GHz, for temperatures betw een 254 and 359 K. Analysis of dielectric data and their comparison wi th results recently obtained on the same system by Brillouin light sca ttering have evidenced a two-step relaxation process. Dielectric spect ra account for the behaviour of the slower process, i.e. the structura l relaxation, while Brillouin spectra are particularly sensitive to th e faster process, i.e. the secondary relaxation. The temperature behav iour of these processes is not in accordance with the predictions of t he mode-coupling theory, while it can be suitably interpreted by a mod el that relates the high-frequency dependence of the dielectric loss c urve to the local chain dynamics and the low-frequency dependence to t he intermolecular correlation.