CURING KINETICS OF CYANATED POLY(ETHER SULFONE)S OF DIFFERENT MOLECULAR-WEIGHT

Three cyanated poly(ether sulfone)s (CPESs) with number-average molecular weights of 910, 1550 and 3240 were synthesized and their polycyclotrimerization kinetics studied by dynamic differential scanning calorimetry (DSC). The resulting apparent activation energies (E(a)) are quite close and range from 87.5 to 92.0 kJ/mol. The corresponding curing reactions in relation to conversion (a) can be expressed with an autocatalytic first-order kinetics d alpha/dt = A (1 + B alpha) (1 - alpha) exp (-E(a)/(RT)). This kind of kinetics can be explained by a mechanism consisting of both a hydroxyl-catalyzed and an autocatalytic path. The lower pre-exponential factor (A) and contribution of autocatalytic reaction (B) for high molecular weight CPES are due to the low concentrations of catalytic species in the starting CPES and the resulting sym-triazine rings, respectively.