Relaxations and phase transitions phenomena in structurally related tyrosine-derived polyarylates

A series of four tyrosine-derived polyarylates with different number of methylene groups in the backbone (y = 2, 4, 6 and 8) were studied by measuring thermally stimulated depolarization currents (TSDC). The low temperature TSDC spectra (80-240 K) were analyzed at two different degrees of hydration to assess the effects of small amounts of water in the observed broad and complex β band. Higher temperature TSDC spectra (250 to 350K) provided the a relaxation peaks associated with the glass transition temperature. The direct signal analysis (DSA) method allowed the decomposition of the complex peaks into elementary processes. The β_i components result from localized motions of molecular segments of variable length molecules whose identities were established in a prior study of polycarbonates. The changes observed in the low and high temperature polarization with the number of backbone methylene groups were interpreted as a combination of flexibility and entanglement phenomena.