Synthesis of nano-scale/polymer core-shell particles, as LPA for unsaturated polyester and vinyl ester resins by the Z supported RAFT were investigated. CTA, BSPA was covalently attached to the surface of silica gel to make Si-BSPA and the RAFT polymerization subsequently occurred on the silica surface to form silica/polymer core-shell particles. BSPA was prepared from the potassium salt of 3-mercaptopropionic acid with excess of carbon disulfide, followed by the addition of benzyl bromide. The product was isolated by acidification of solution with hydrochloric acid. Before grafting of CTA on the silica gel, it was needed to activate the silica surface by boiling with hydrochloric acid. The nano-scale silica particle was synthesized by a two-stage hydrolysis of silicon powder in aqueous medium. The structure and morphology of the silica particles were characterized via TEM, DLS, and FT-IR. Si-BSPA was synthesized by reaction of the functionality of the surface by reacting the activated silica particles with 4-(chloromethyl) phenyltrimethoxysilane. RAFT polymerization of MA mediated by Si-BSPA was investigated, where of the initial concentration of monomer.