The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)-block-poly(methyl methacrylate) (PVAc-b-PMMA) as low-profile additives (LPAs) on the glass-transition temperature and mechanical properties of low-shrink unsaturated polyester resin (UP) were investigated by an integrated approach of determining static phase characteristics, reaction kinetics, cured sample morphology, and property measurements. The factors that, according to Takayanagi mechanical models, control the glass-transition temperature in each phase region of the cured samples, as identified by both the thermally stimulated currents method and dynamic mechanical analysis, and the mechanical properties are discussed. (c) 2006 Wiley Periodicals, Inc.