INFLUENCE OF PROCESSING CONDITIONS ON SHRINKAGE BEHAVIOR OF LOW PROFILE UNSATURATED POLYESTER RESINS .1. SYSTEMS WITHOUT FILLERS

Blends of unsaturated polyester resin and polyvinylacetate (PVAc) were molded with a new instrument called the Plastoreactomat (PRM). The sh rinkage and exothermic peak of polymerization were recorded during mod ing, and the influence of the processing conditions (pressure and temp erature) on these phenomena and on the morphology was investigated for various PVAc contents. Within the limits of this study, it was found that shrinkage increases as the temperature and pressure increase. The se results are discussed in terms of a competition between the phase s eparation and the reaction rates. In addition, it was verified that a co-continuous two-phase system consisting of the PVAc and the polyeste r network enhances the low-profile behavior.