Cure Schedule of Epoxides and Their Sulfur-Containing Derivatives. Kinetic Study

Abstract

A series of model epoxides and their sulfur-containing derivatives have been 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 activation energy (E) values of the cure process are higher for (1,3-oxothiolane-2-thione)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 means of advanced non-linear regression based approach which made it possible to determine reaction models of the cure, changing from ‘reaction 1st order’ to ‘one-dimensional diffusion’ models. Other aspects, such as the possibility of existence of non-elastically contributing species–the products of inter-or intramolecular cyclization–which are not incorporated directly into the growing network, but may changes the mechanism on molecular, ‘transition-state’ level, are also discussed. Finally, kinetic predictions of the system behavior in extrapolated range of degree of cure, time and temperature are presented on the basis of obtained kinetic parameters.