Provided is a polymer particle comprising (a) a core polymer comprising (i) polymerized units of one or more Si-containing monomers; (ii) polymerized units of one or more monovinyl acrylic monomers (ii); and (iii) polymerized units of one or more graftlinkers that have no silicon atoms; (b) a shell polymer comprising polymerized units of one or more acrylic monomers. Also provided is a composition comprising polyvinyl chloride and a plurality of the polyer particles.