CHAIN FRAGMENTATION UNDER LIQUID-STATE AND SOLID-STATE CONDITIONS

Thermally activated fragmentation of copolycarbonates PC (T(x)A1-x) of bisphenol A (unit CA) and the heat-sensitive diol 1,1,2,2-tetraethyl-1,2-di-(p-hydroxy)phenylethane (unit CT) was studied in the bulk, i.e., in the pure copolymers and in their blends with the polycarbonates of bisphenol A (PCA) or tetramethyl bisphenol A (TMPC). Fragmentation proceeds via dissociation followed by disproportionation at the central C-C bond of the unit CT. The reaction has rates that are convenient to study near the glass transition temperature. The "chemical" time constants-tau for the entire reaction and tau-2 for the disproportionation step compete with the "physical" time constants-delta(alpha) for segmental motion and delta(q) for fragment diffusion. A cage effect is observed below tau-2 = delta(alpha), and effects of delayed matrix response below tau = delta(alpha) and tau = delta(q). Owing to the two latter effects, parameters such as the glass transition temperature and the structure factor of concentration fluctuations do not respond primarily to the fragmentation, but rather to subsequent relaxation and diffusion processes in the polymer matrix.