Curing kinetics of epoxy-urethane copolymers

The cure of the epoxy resin diglycidyl ether of bisphenol A (Araldyt GY9527 ) with a mixture of cycloaliphatic amines (Distraltec) was studied, and the focus was on the effect of the copolymerization with a commercial polyuret hane (PU) elastomer (Desmocap 12). A simplified phenomenological model was proposed to represent the copolymerization reaction. It considered the effe ct of the temperature and the concentration of the elastomer on the reactio n rate, and it was simple enough to be included in models of processing con ditions. A nonlinear regression analysis of the experimental conversion dat a obtained from differential scanning calorimetry was utilized to End the b est fitting parameters to Kamal's equation for the chemically controlled pa rt: of the reaction (short times) under isothermal and constant heating-rat e conditions. The Rabinowitch approach together with the Addam-Gibbs theory was utilized to introduce the effect of diffusion control at the end of th e reaction on the overall constant for the reaction rate. The Di Benedetto equation was used to predict the conversion at which vitrification fakes pl ace for each run. Experimental results for conversions higher than this cri tical conversion were utilized to obtain information about the diffusion ki netic constant using a nonlinear regression analysis as previously. The ove rall model obtained was used to calculate a calorimetric conversion and rea ction rate as functions of time, which was in excellent agreement with the experimental results. The addition of PU elastomers affected the values of the activation energies of the chemically and diffusion controlled parts of the reaction, as well as the final conversion reached by the epoxy-amine s ystem. The proposed model allowed prediction of all the observed features u sing parameters that were independent of the temperature of the curing reac tion. (C) 2001 John Wiley & Sons, Inc.