Reaction kinetics modeling and thermal properties of epoxy-amines as measured by modulated-temperature DSC. I. Linear step-growth polymerization of DGEBA plus aniline

A mechanistic approach including both reactive and nonreactive complexes can successfully simulate both nonreversing (NR) heat flow and heat capacity (C-p) signals from modulated-temperature DSC in isothermal an nonisothermal reaction conditions for different mixtures of diglycidyl ether of bisphenol A + aniline. The reaction of the primary amine with an epoxy-amine complex initiates cure (E-1A1 = 80 kJ mol(-1)), whereas the reactions of the primary amine (E-1OH = 48 kJ mol(-1)) and secondary amine (E-2OH = 48 kJ mol(-1)) with an epoxy-hydroxyl complex are rate determining from about 2% epoxy conversion on. The reliability of the proposed mechanistic model was verified by experimental concentration profiles from Raman spectroscopy. When cure temperatures are chosen inside or below the full cure glass-transition region, vitrification takes place partially or completely, respectively, as can be concluded from the magnitude of the stepwise decrease in C-p. The effect of the epoxy conversion (x) and mixture composition on thermal properties such as the glass-transition temperature (T-g), the change in heat capacity at T-g[DeltaC(p)(T-g)], and the width of the glass transition region (DeltaT(g)) are considered. The Couchman relationship, in which only T-g and DeltaC(p)(T-g) of both the unreacted and the fully reacted systems are needed, was evaluated to predict the T-g - x relation by using simulated concentration profiles. (C) 2004 Wiley Periodicals, Inc.