CURE OF UNSATURATED POLYESTER RESINS .2. INFLUENCE OF LOW-PROFILE ADDITIVES AND FILLERS ON THE POLYMERIZATION REACTION, MECHANICAL-PROPERTIES AND SURFACE RUGOSITIES

The effects of poly(vinyl acetate) (PVAc) and CaCO3 on the cure kineti cs, mechanical properties and surface rugosities of unsaturated polyes ter (UP) resins were studied. When the ratio of styrene to UP unsatura tion was kept constant, PVAc did not have any effect on cure kinetics, maximum conversion or glass transition temperature of the crosslinked UP resin. The addition of CaCO3 led to a decrease in the induction pe riod of the copolymerization, without any significant action on the su bsequent cure rate. The addition of PVAc was only effective in promoti ng an excellent copy of the mould surface at concentrations higher tha n the critical one leading to co-continuous structures (8 wt% for the formulation used in the present study). The use of PVAc at concentrati ons beyond the critical value did not produce further improvements in the surface quality. The simultaneous use of both PVAc and CaCO3 in UP formulations led to materials with very low strength and impact resis tance, and with only a moderate ability to reproduce the mould surface .