Cure schedule of epoxides and their sulfur-containing derivatives. Kineticstudy

A series of model epoxides and their sulfur-containing derivatives have bee n cured by hexahydrophthalic anhydride. The curing process was kinetically analysed using differential scanning calorimetry data. It has been found by means of Friedman and Ozawa-Flynn-Wall methods that the apparent activatio n energy (E) values of the cure process are higher for (1,3-oxothiolane-2-t hione)s than for model epoxides and lay in the range of 100.1-119.6 kJ mol( -1). Some instability regions of E vs. degree of cure, which were observed for all samples under investigation, confirm the complex kinetic scheme and comes probably from intermediate steps between different rate-controlling mechanisms. This supposition was supported by further kinetic analysis by m eans of advanced non-linear regression based approach which made it possibl e to determine reaction models of the cure, changing from 'reaction 1st ord er' to 'one-dimensional diffusion' models. Other aspects, such as the possi bility of existence of non-elastically contributing species-the products of inter-or intramolecular cyclization-which are not incorporated directly in to the growing network, but may changes the mechanism on molecular, 'transi tion-state' level, are also discussed. Finally, kinetic predictions of the system behavior in extrapolated range of degree of cure, time and temperatu re are presented on the basis of obtained kinetic parameters.