Cure Kinetics of a Diglycidyl Ether of Bisphenol A Epoxy Network (n 5 0) with Isophorone Diamine Francisco Fraga, 1 Marcos Penas, 1 Carlos Castro, 1 Eugenio Rodrı ´guez-Nu ´n ˜ ez, 1 Jose ´ Manuel Martı ´nez-Ageitos 2 1 Departamento de Fı ´sica Aplicada, Facultade de Ciencias, Universidade de Santiago de Compostela, Campus Universitario, 27002 Lugo, Spain 2 Departamento de Enxen ˜erı ´a Quı ´mica, Facultade de Ciencias, Universidade de Santiago de Compostela, Campus Universitario, 27002 Lugo, Spain Received 15 January 2007; accepted 24 May 2007 DOI 10.1002/app.26989 Published online 7 September 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The study of the cure reaction of a digly- cidyl ether of bisphenol A epoxy network with isophor- one diamine is interesting for evaluating the industrial behavior of this material. The total enthalpy of reaction, the glass-transition temperature, and the partial enthal- pies at different curing temperatures have been deter- mined with differential scanning calorimetry in dynamic and isothermal modes. With these experimental data, the degree of conversion and the reaction rate have been obtained. A kinetic model introduces the mechanisms occurring during an epoxy chemical cure reaction. A modification of the kinetic model accounting for the influ- ence of the diffusion of the reactive groups at high con- versions is used. A thermodynamic study has allowed the calculation of the enthalpy, entropy, and Gibbs free energy. Ó 2007 Wiley Periodicals, Inc. J Appl Polym Sci 106: 4169–4173, 2007 Key words: differential scanning calorimetry (DSC); glass transition; kinetics (polym.); resins INTRODUCTION The physicochemical properties of polymeric com- pounds based on structural resin hardeners are mainly determined by the curing conditions. A widely used technique in the study of these systems is differential scanning calorimetry (DSC), which allows the evaluation of the thermal behavior of a material. An epoxy system based on diglycidyl ether of bisphenol A (number of monomers of the epoxy resin (n) 5 0) and isophorone diamine is used in revet- ments and paints. A good knowledge of its cure kinetics allows us to determine suitable conditions for the structural formation of the material. The pur- pose of this work is to study the cure kinetics of that epoxy network. In the first experimental step, the total enthalpy of reaction (DH t ) and the glass-transition temperature (T g ) have been determined with DSC in a dynamic mode. In the second experimental step, the partial enthalpy (DH T ) values at different curing tempera- tures have been determined with DSC in an isother- mal mode. From these experimental data, the con- versions and reaction rates for each curing tempera- ture have been calculated. These data have allowed us to determine the ki- netic coefficients and the global order of the cure reaction with the Sourour and Kamal model, 1 which incorporates simultaneously the n-order and autoca- talytic mechanisms. With this model, the constant rates of the two mechanisms and their activation energies have been determined. Because of the onset of gelation, a gradual decrease in the reaction rate and an increase in the viscosity can be observed, especially at high con- versions. Therefore, a modification of the kinetic model proposed by Chern and Polheim 2–4 has been used to study the diffusion reaction rate. This model is based on free-volume considerations, introducing a diffusion factor into the reaction rate of the system that tends to unity at low conversions at which the reaction is controlled by the chemical kinetics and that tends to zero at high conversions at which the reaction decreases. This seems reason- able because the molecular weight drastically increases the hindrance of the mobility of the reac- tive groups. This global kinetic model has been used successfully to study the cure kinetics of other epoxy systems. 3–8 Finally, a thermodynamic study based on the theory of Eyring 9 and Evans and Polyani 10 has allowed the calculation of the changes in the en- thalpy (DH # ), entropy (DS # ), and Gibbs free energy (DG # ) at different curing temperatures during the formation of the activation complex. Correspondence to: F. Fraga (franfrag@lugo.usc.es). Journal of Applied Polymer Science, Vol. 106, 4169–4173 (2007) V V C 2007 Wiley Periodicals, Inc.