PURPOSE: To obtain the subject polymer comprising a specific constitution, useful as a contraction-reducing agent for unsaturated polyester resins and giving unsaturated polyester resin molded products excellent in moldability, transparency and surface luster.
CONSTITUTION: The objective polymer comprises (A) 50-90wt.% of a core layer formed of the crosslinked polymer obtained from monomers containing ≥50wt.% of an aromatic vinyl (preferably styrene) and (B) 50-10wt.% of a shell layer formed of the polymer obtained from monomers containing ≥50wt.% of methyl methacrylate, and has a refractive index of 1.52-1.58. This polymer is produced by emulsion-polymerizing 80-99.5wt.% of an aromatic vinyl, 0-20wt.% of a copolymerizable vinylic monomer, 0.1-1wt.% of divinyl benzene as a crosslinkable monomer and 0-1wt.% of a graft polymer for the formation of the layer A, and subsequently emulsion-polymerizing 80-95wt.% of methyl methacrylate, 0-2wt.% of a crosslinkable monomer and 0-2wt.% of a graft monomer for the formation of the shell layer B.
OKAYA SUSUMU
AKIYAMA KOICHI
SAKURAI MASAHITO
