Curing kinetics and thermal property characterization of a bisphenol-S epoxy resin and DDS system

The kinetics of the cure reaction for a system of bisphenol-S epoxy resin ( BPSER), with 4,4'-diaminodiphenyl sulfone (DDS) as a curing agent was inves tigated with a differential scanning calorimeter (DSC). Autocatalytic behav iour was observed in the first stages of the cure which can well be describ ed by the model proposed by Kamal, using two rate constants, k(1) and k(2), and two reaction orders, m and n. The overall reaction order, m+n, is in t he range 2 similar to2.5, and the activation energy for k(1) and k(2) was 8 6.26 and 65.13 kJ mol(-1), respectively. In the later stages, a crosslinked network was formed and diffusion control was incorporated to describe the cure. The glass transition temperature (T-g) of the BPSER/DDS samples parti ally cured isothermally was determined by means of torsional braid analysis (TBA) and the results showed that the reaction rate increased with increas ing T-g, in terms of rate constant, but decreased with increasing conversio n. It was also found that the -SO2-group both in the epoxy resin and in the hardener increases the T-g values of the cured materials compared with tha t of BPAER. The thermal degradation kinetics of this system was investigate d by thermogravimetric analysis (TGA). It illustrated that the thermal degr adation of BPSER/DDS has nth order reaction kinetics. (C) 2000 Society of C hemical Industry.