Suspension-emulsion combined polymerization(SECP) process

in which methyl methacrylate (MMA) emulsion polymerization constituents(EPC) were drop-wisely added to styrene(St) suspension polymerization(SP) system at different stages of St suspension polymerization

was applied to prepare polystyrene/poly (methyl methaerylate) (PS/PMMA) composite particles．The particle features of the resuhing polymer particles and the particle formation mechanism of SECP were studied．It was found that PMMA latex particles gradually coagulated with PS particles after the addition of EPC at the mid stage of St suspension polymerization

and core-sheU structure PS/PMMA composite particles with greater size were finally formed．St/MMA copolymer particles composed of primary particles and imperfect core-shell structure PS/PMMA composite particles were obtained by adding EPC at the initial and late stages of St SP

respectively．According to the particle formation mechanism of St suspension polymerization and the vafiations of particle features of PS/PMMA composite particles

a particle formation mechanism of St-MMA SECP was proposed．