Chemorheology of thermosetting resins. III. Effect of low-profile additive on the chemorheology and curing kinetics of unsaturated polyester resin

An experimental study was conducted to investigate the effect of low‐profile thermoplastic additives on the rheological behavior during cure and the curing kinetics of unsaturated polyester resin. For the study, a general‐purpose polyester resin was used and two different types of thermoplastic additive, poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA), were used as low‐profile additives. It has been found that, during cure, the resin/PMMA system exhibits shearthinning behavior even before the cure time reaches the critical value tη∞ whereas the resin/PVAc system does not. Also, both PVAc and PMMA help reduce the shrinkage of the resin during cure. However, our study shows that shrinkage control becomes effective only when the shear rate is greater than a certain critical value. The curing behavior determined with the aid of differential scanning calorimetry (DSC) shows that the rate of cure and the final degree of cure are decreased when the amount of low‐profile additive is increased.