RELAXATIONS IN THERMOSETS .26. ULTRASONIC STUDIES OF THE TEMPERATURE-DEPENDENCE OF CURING KINETICS OF DIGLYCIDYL ETHER OF BISPHENOL-A WITH CATALYST

Longitudinal velocity and attenuation of the unreacted diglycidyl ethe r of bisphenol-A and dimethylbenzylamine mixture have been measured fo r 1 MHz ultrasonic frequency. These are combined with our earlier data [Alig et al., Acta Polymerica, Vol. 40, p. 590 (1989)], which were me asured during the curing process of the thermoset, and then analyzed i n terms of a process involving a negative feedback between molecular d iffusion and chemical reaction. The complex plane plots of the real an d imaginary components of the longitudinal modulus are fitted to a str etched exponential relation, and the structural relaxation time is cal culated at different stages of curing at temperatures in the range 333 -403 K. The results are compared against the calorimetric, dielectric, and viscosity measurements and it is shown that, at least for two cas es, gelation time can be observed from the longitudinal modulus data. (C) 1994 John Wiley & Sons, Inc.