Quasielastic light scattering in poly(methylmethacrylate)

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Abstract
Quasielastic light scattering (QLS) in the glassy polymer poly(methylmethacrylate) is investigated in the temperature range 12-470 K. Raman spectra were measured in the frequency interval 3-600 cm-1. The detailed temperature dependence of the Raman intensity at some fixed frequencies, omega =5, 8, 20 cm-1 is obtained. The influence of the quenching on the QLS is investigated. It is shown that there are two characteristic temperature regions with different dependences of the QLS intensity on temperature. The first one is for T80-100 K. Here the relaxation time is nearly constant while the reduced Raman intensity increases with an activation energy of the order of 700 K up to the glass transition temperature Tg. The spectral dependence 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 depends 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 Lorentzian. The data obtained are considered within the frames of the existing models of QLS.