The Effect of Epoxy Excess on the Kinetics of an Epoxy–Anhydride System A. N. MAURI, C. C. RICCARDI Institute of Materials Science and Technology (INTEMA), University of Mar del Plata and National Research Council (CONICET), Av. J. B. Justo 4302, B7608FDQ Mar del Plata, Argentina Received 27 February 2001; accepted 18 September 2001 Published online 18 June 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.10867 ABSTRACT: The uncatalyzed cure of a commercial tetrafunctional epoxy monomer TGDDM (N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane) with hexahydroph- thalic anhydride (HHPA), using variable stoichiometric ratios is reported. The reaction was followed by differential scanning calorimetry (DSC). Two kinds of experiments were performed: (1) fresh samples were run at several heating rates, and (2) samples, precured a certain time in an oil bath at constant temperature (i.e., 80 to 120°C), were run at 10°C/min. Two peaks were observed in the case of the epoxy excess but only one for the stoichiometric formulation: the peak at low temperature was attributed to the epoxy copolymerization with the anhydride while the peak at high temperature was attributed to the epoxy homopolymerization. The catalytic effect of the OH groups present in the epoxy monomer on the copolymerization reaction was demonstrated by the decrease in the activation energy of the propagation step when increasing the epoxy excess. There is a catalytic effect of the copolymerization product on the homopolymer- ization reaction. Our simplest model, proposed previously for a catalyzed epoxy/anhy- dride system [J. Polym. Sci. Part B: Polym. Phys. Ed., 37, 2799 (1999)], can be used to fit both isothermal and dynamical kinetic data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2342–2349, 2002 INTRODUCTION A simple kinetic model was recently proposed to study epoxy/anhydride polymerization initiated by tertiary amines. 1 It enabled us to provide an explanation of the inconsistencies found in previ- ous kinetic studies. These inconsistencies may be summarized as follows: (a) first-order kinetics can fit both dynamic and isothermal differential scan- ning calorimetry tests, but with significantly dif- ferent values of the apparent activation ener- gy, 2–5 and (b) phenomenological autocatalytic ki- netic expressions with different orders can also be used to fit kinetic results under both isothermal and nonisothermal conditions, using a single value of the apparent activation energy. 6–8 The simplest polymerization model consists of two rel- evant steps: a reversible reaction transforming an inactive species (i) into an active one (i*), and the usual propagation step where the monomer, m, reacts with the active specie. In this case m rep- resents a couple of epoxy and anhydride groups because, once formed, the active epoxides at chain ends react almost immediately with anhydride monomers. 9,10 It was also assumed that the chain transfer step regenerated the active species. In a previous study of a tetrafunctional epoxy monomer with hexahydrophthalic anhydride (HHPA), it was pointed out that OH groups, present as impurities in the technical epoxy, cat- alyze the epoxy–anhydride copolymerization, and that the epoxy homopolymerization reaction be- Correspondence to: C. C. Riccardi (criccard@fi.mdp.edu.ar). Journal of Applied Polymer Science, Vol. 85, 2342–2349 (2002) © 2002 Wiley Periodicals, Inc. 2342