The thermal, dynamic mechanical, and mechanical properties and morphology of two series of semi-interpenetrating polymer networks (s-IPNs) based on linear poly(vinyl acetate) (PVAc) and a crosslinked n-butyl acrylate/1,6-hexanediol diacrylate copolymer were investigated. The s-IPN composition was varied with different monoacrylate/diacrylate monomer ratios and PVAc concentrations. The crosslinking density deeply affected the thermal behavior. The results showed that a more densely crosslinked acrylate network promoted phase mixing and a more homogeneous structure. The variation in the linear polymer concentration influenced both the morphology and mechanical properties. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2675-2683, 2009