Effects of reactive low-profile additives on the volume shrinkage and internal pigmentability for low-temperature cure of unsaturated polyester

The effects of reactive poly(vinyl acetate)block-poly(methyl methacrylate) (PVAc-b-PMMA) and poly,(vinyl acetate)-block-polystyreiie (PVAc-b-PS) as low-profile additives (LPA) on the volume shrinkage characteristics and internal pigmentability for low-shrink unsaturated polyester resins (UP) during the cure at 30 degrees C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerizations, using polymeric peroxides (PPO) as initiators. Depending on the LPA composition and molecular weight, the reactive LPA could lead to a reduction of cyclization reaction for UP resin during the cure, and would be favorable for the decrease of intrinsic polymerization shrinkage after the cure. The experimental results have been explained by an integrated approach of measurements for the static phase characteristics of the styrene (ST)/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), optical microscopy (OM), and image analysis. Based on the Takayanagi mechanical model, factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts have been explored. (c) 2006 Wiley Periodicals, Inc.