Effect of diluents on the decomposition behavior of vinyl ester resin

An acidic vinyl ester resin (∼6 mg KOH per gram of solid) was prepared by reacting a bisphenol-A-based epoxy resin with acrylic acid in the presence of tributylamine. The acrylated epoxy resin thus obtained was characterized by Fourier transform infrared spectroscopy. Five samples of vinyl ester resin containing styrene and methyl methacrylate (MMA) in the weight ratios 40:0, 30:10, 20:20, 10:30, and 0:40 were prepared at 30°C. These samples were cured, using 2 phr benzoyl peroxide, at 90 ± 2 °C for 1 h. The decomposition behavior of all the samples was studied by thermogravimetric analysis (TGA) at 10°C min⁻¹. The TG and dynamic thermogravimetry (DTG) thermograms showed single-step degradation in the individual cases of styrene and MMA, whereas a two-step degradation process was observed when styrene was mixed with MMA in any proportion. For all the samples, the order of the reaction was one for the first step. This value was calculated with the Coats and Redfern equation in accordance with the best-fit analysis and further confirmed by linear regression analysis. From this value of reaction order (n), the activation energy (E) and pre-exponential factor (Z) were calculated, and the validity of the data was checked by statistical analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1952–1956, 2003