Study of fast relaxation in a glassy polymer by far-IR spectroscopy

The temperature dependence of the far-IR spectra of glassy polymethylmethacrylate is studied in the range of $\nu$ = 10–130 cm$^{-1}$ at temperatures from 90 to 420 K. The analysis of the spectra revealed absorption corresponding to two rapid relaxation processes: (1) 180$^\circ$-rotation of the OCO plane of the side groups and (2) reorientation of the links of the main chain. The activation energies of these processes are determined.