New thermosets obtained by cationic copolymerization of DGEBA with γ-caprolactone with improvement in the shrinkage.: II.: Time-temperature-transformation (TTT) cure diagram

Mixtures of diglycidylether of bisphenol A (DGEBA) with different proportions of gamma-caprolactone (gamma-CL) were cured with ytterbium triflate as initiator. The curing was studied with differential scanning calorimetry (DSC) and thermo mechanical analysis (TMA). The results are presented in the form of a time-temperature-transformation diagram. The kinetic analysis was performed by means of the isoconversional integral procedure and the kinetic model was also determined using the Coats-Redfern method. Gelation was determined by means of combined experiences of DSC and TMA. The relationship between the glass transition temperature (T-g) and the degree of conversion alpha was determined by DSC. Using the isoconversional lines and the T-g-alpha relationship, the vitrificacion curve was obtained. The methodology developed makes it possible to obtain the TTT diagram using only no-isothermal experiments with equivalent results to those using classical isothermal procedures. The addition of gamma-CL accelerates the curing and reduces the shrinkage after gelation and consequently the internal stresses in the material. (c) 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3406-3416, 2007