MOSSBAUER STUDIES OF POLYMERS IN THE GLASSY STATE AND NEAR THEIR GLASS-TRANSITION

Mossbauer absorption spectra of glassy block and copolymers with low T(G) containing ferrocene have been recorded in a wide temperature range (4-330 K) to investigate the dynamical processes of the system, in the glassy state and around the glass transition. An inhomogeneous broadening due to conformational substates with different hyperfine parameters found at lower temperatures becomes motionally narrowed above 40 K. Whereas in the glassy state both the block and the copolymers reveal the same vibrational behaviour, we found differences in the vicinity of their respective glass transitions. For the block polymer an anomalous decrease of the recoilfree fraction f(A) was found above the static glass transition. In agreement with neutron data on other polymers we attribute this behaviour to an onset of motions of the ferrocene units of higher than 10(10) Hz. For the copolymers, however, a departure of 1n f(A) from linearity was detected already far below the static T(G). We propose that this is caused by residual solvents which allow an easier cooperative rearrangement of the segments even below T(G). First attempts to interpret the Mossbauer data by means of the predictions of the mode coupling theory are reported.