Copolymerization kinetics of styrene/vinyl-ester systems: Low temperature reactions

Vinyl-ester (VE), synthesized by the addition reaction of methacrylic acid and diglycidyl ether of his-phenol A (DGEBA) epoxy, and styrene react via bulk free radical chain growth copolymerization to form a crosslinked network polymer. Vital clues regarding the development and the structure of the network were obtained from the study of copolymerization kinetics of styrene/VE systems. Fourier transform infrared (FTIR) spectroscopy was used to obtain the individual fractional conversion rates of both the monomers. The conversion versus time data for both styrene and VE was fit to an autocatalytic kinetic model. The autocatalytic model was found to adequately replicate the kinetic data over the entire Life of cure. In this investigation, the effects of styrene concentration, temperature, catalyst concentration, and initiator concentration on cure kinetics of styrene/VE systems were studied. The conversion profiles of both styrene and VE were used to obtain the reactivity ratios of the two monomers. The reactivity ratios were evaluated to be close to zero, suggesting that initially alternating copolymerization is favored over homopolymerization. The cure behavior of vinyl-ester resins is affected not only by the chemical reactivity of the monomers toward the free radicals, but also by diffusion effects, phase separation, and microgel formation. The interplay of these factors controls the kinetics of cure, thereby affecting the physical and chemical properties of the resulting polymer.