CURE KINETICS OF ELEMENTARY REACTIONS OF A DGEBA DDS EPOXY-RESIN .1. GLASS-TRANSITION TEMPERATURE VERSUS CONVERSION

The influence of elementary reactions (linear polymerization and cross linking) on the development of the glass transition temperature (T(g)) of diglycidyl ether of bisphenol A/diaminodiphenylsulfone (DGEBA/DDS) epoxy resin system has been analysed quantitatively according to a pr oposed model. The model was derived on the basis of the reaction mecha nisms observed in the curing system and the assumption that the T(g) h as individual linear relationships with the degree of conversion of th e two reactions. The conversions of elementary reactions during the cu re were obtained experimentally by measuring the changes in the concen trations of epoxy, primary and secondary amine groups with time by nea r-infra-red spectroscopy. The T(g) values were measured by differentia l scanning calorimetry (d.s.c.). In addition, and for the purpose of c omparison, the overall conversion of the system was also obtained from d.s.c. in a dynamic scanning mode. The conversion-time data from the two different techniques were consistent. The proposed model successfu lly predicted the separate increases in T(g) due to the linear polymer ization and due to the crosslinking reactions. The Di Benedetto equati on and the viscoelastic model of Gan et al. are also discussed.