MOLECULAR RELAXATION MECHANISMS OF TYROSINE-DERIVED POLYCARBONATES BYTHERMALLY STIMULATED DEPOLARIZATION CURRENTS

A series of tyrosine-derived polycarbonates with different lengths (2 less than or equal to n less than or equal to 8) for the alkyl ester p endent chain were studied by measuring thermally stimulated depolariza tion currents (TSDC). The observed spectra could be separated into thr ee regions: the low-temperature zone with a broad, complex beta band ( 80-240 K), the intermediate zone (250-300 K), and the high-temperature zone (300-400 K) with a sharp a peak. The application of direct signa l analysis (DSA) to decompose the complex peaks into elementary proces ses led to the determination of the relaxation time distribution and t emperature dependence of each process. The variation of the relaxation parameters as a function of the pendent chain length facilitated the tentative identification of the relaxation mechanisms responsible for the observed current peaks. It is proposed that as the temperature inc reases one observes, first, the individual motion of each polar group, then the concerted motion of the entire pendent chain, and, last, the movement of the polymer backbone. (C) 1997 John Wiley & Sons, Inc.