QUASI-ELASTIC LIGHT-SCATTERING IN POLY(METHYLMETHACRYLATE)

Quasielastic light scattering (QLS) in the glassy polymer poly(methylm ethacrylate) is investigated in the temperature range 12-470 K. Raman spectra were measured in the frequency interval 3-600 cm(-1). The deta iled temperature dependence of the Raman intensity at some fixed frequ encies, omega = 5, 8, 20 cm(-1) is obtained. The influence of the quen ching on the QLS is investigated. It is shown that there are two chara cteristic temperature regions with different dependences of the QLS in tensity on temperature. The first one is for T < 50-80 K, where the re duced Raman intensity increases with a characteristic activation energ y of the order of 30 K. The second region is the high-temperature one: T > 80-100 K. Here the relaxation time is nearly constant while the r educed Raman intensity increases with an activation energy of the orde r of 700 K up to the glass transition temperature T-g. The spectral de pendence of the relaxation contribution, found by a subtraction of the lowest-temperature (12 K) spectrum from the current one, I(T,omega)/( n(omega)+1), demonstrates a relaxational beta peak which weakly depend s on temperature. Its characteristic frequency is of the order of its width and is equal to 8-10 cm(-1). The peak can be well fitted by a Lo rentzian. The data obtained are considered within the frames of the ex isting models of QLS.