The effects of three series of self-synthesized poly(methyl methacrylate) (PMMA)-based low-profile additives (LPAs), including PMMA, poly(methyl methacrylate-co-butyl acrylate), and poly(methyl methacrylate-co-butyl acrylate-co-maleic anhydride) with different chemical structures and MWs on the volume shrinkage characteristics and internal pigmentability for low-shrink unsaturated polyester (UP) resins during curing were investigated by an integrated approach of static phase characteristics of the ternary styrene (ST)/UP/LPA system, reaction kinetics, cured-sample morphology, microvoid formation, and property measurements. The relative volume fraction of microvoids generated during the cure was controlled by the stiffness of the UP resin used, the compatibility of the uncured ST/UP/LPA systems, and the glass-transition temperature of the LPAs used. On the basis of the Takayanag! mechanical model, the LPA mechanism on volume shrinkage control, which accounted for phase separation and microvoid formation, and factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts are discussed. (C) 2004 Wiley Periodicals, Inc.