SIMULTANEOUS DIFFERENTIAL SCANNING CALORIMETRY AND NEAR-INFRA-RED ANALYSIS OF THE CURING OF TETRAGLYCIDYLDIAMINODIPHENYLMETHANE WITH DIAMINODIPHENYLSULPHONE

The crosslinking reaction of tetraglycidyl-4,4'-diaminodiphenylmethane with 27% 4,4'-diaminodiphenylsulphone at 150-degrees-C and 170-degrees-C was studied by near-i.r. spectroscopy while simultaneously recording the heat flow by isothermal differential scanning calorimetry (d.s.c.). From the absolute concentrations of primary, secondary and tertiary amine groups and the epoxy, hydroxyl and ether groups measured throughout the reaction, instantaneous rate curves were obtained and used along with reported reaction enthalpies to calculate heat flow curves for comparison with the d.s.c. data. It was found that previous assumptions of a constant reaction enthalpy were incorrect and values of - 83 +/- 2, - 131 +/- 9 and - 65 +/- 6 kJ mol-1 for epoxide reaction with primary amine, secondary amine and hydroxyl, respectively, gave the best fit between near-i.r. and d.s.c. data. Deviations between fitted and experimental data after gelation were attributed to heat capacity changes on vitrification and allowed a 'true' isothermal baseline to be constructed. From the corrected isothermal d.s.c. data and the absolute concentration of epoxide consumed, an average reaction enthalpy of - 92 +/- 1 kJ mol-1 was obtained. Reasons for discrepancies between these and scanning d.s.c. data are considered.