Abstract
The effects of molecular weights and molecular structure of styrene(st)-based and vinyl acetate(VAc)-based low-profile additive(LPA) on the miscibility, reaction kinetics of UP/LPA system and on the linear shrinkage, water absorption rate, surface roughness, surface gloss and pigmentability and mechanical properties of bulk molding compound (BMC) were investigated . Results showed that the plasticizing effect of LPA on the unsaturated polyester (UP) decreased with the increasing of the molecular weight of LPA . The curing rate of UP/LPA system also decreases with increasing of the molecular weight of LPA due to the chain entanglement effect .Water absorption of BMC increases as the molecular weight of LPA increases implies that more microvoids were formed inside the BMC, results in a lower linear shrinkage rate, and worse pigmentability . However, good shrinkage control LPA does not necessarily lead to a smooth surface and better suface gloss.The mechanical properties of BMC also decreases as the molecular weight of LPA increases due to the poor adhesion between LPA and UP phase. Modified LPAs posses better compatibility with UP, the final curing conversion of UP is elevated, both good shrinkage control and surface properties are also observed.The inhenced adhesion between UP/LPA is responsible for significant improvement of tensile strength, tensile modulus, and flexural modulus .