Abstract: PB-g-SAN copolymer prepared via seeded emulsion polymerization were meltblended with SAN resin forming an ABS resin. The shell thickness of PBgSAN copolymer was found to be the most important factor for the toughness of ABS resin. When the shell thickness was greater than a critical value of 117 nm, the modulus of these coreshell particles was too high to be flexible, and thus not efficient as rubbery modifiers. On the other hand, when the shell thickness was less than another critical value of 32 nm, the particles was not fully covered by the shell, the particles could not toughen SAN resin efficiency. When the shell thickness of particles was between 32 nm and 117 nm, the toughening of SAN was observed.

Key words: acrylonitrilestyrene copolymer grafted polybutadiene copolymer, acrylonitrilestyrene copolymers, shell thickness, toughening.