Curing Kinetics of Epoxy-Urethane Copolymers

P.M. STEFANI; S.M. MOSCHIAR; M.I. ARANGUREN

JOURNAL OF APPLIED POLYMER SCIENCE

wiley

Año: 2001 vol. 79 p. 1771 - 1779

0021-8995

The cure of the epoxy resin diglycidyl ether of bisphenol A (AraldytGY9527) with a mixture of cycloaliphatic amines (Distraltec) was studied, and the focuswas on the effect of the copolymerization with a commercial polyurethane (PU) elastomer(Desmocap 12). A simplified phenomenological model was proposed to representthe copolymerization reaction. It considered the effect of the temperature and theconcentration of the elastomer on the reaction rate, and it was simple enough to beincluded in models of processing conditions. A nonlinear regression analysis of theexperimental conversion data obtained from differential scanning calorimetry wasutilized to find the best fitting parameters to Kamal’s equation for the chemicallycontrolled part of the reaction (short times) under isothermal and constant heating-rateconditions. The Rabinowitch approach together with the Addam–Gibbs theory wasutilized to introduce the effect of diffusion control at the end of the reaction on theoverall constant for the reaction rate. The Di Benedetto equation was used to predictthe conversion at which vitrification takes place for each run. Experimental results forconversions higher than this critical conversion were utilized to obtain informationabout the diffusion kinetic constant using a nonlinear regression analysis as previously.The overall model obtained was used to calculate a calorimetric conversion and reactionrate as functions of time, which was in excellent agreement with the experimentalresults. The addition of PU elastomers affected the values of the activation energies ofthe chemically and diffusion controlled parts of the reaction, as well as the finalconversion reached by the epoxy–amine system. The proposed model allowed predictionof all the observed features using parameters that were independent of the temperatureof the curing reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1771–1779, 2001Key words: epoxy–amine; modified epoxy resins; polyurethane modifiers; curingkinetics; diffusion control