A batch-semi-batch two-stage reversible addition-fragmentation chain transfer(RAFT) mini-emulsion polymerization of styrene was investigated.It was found that the starting point of the feeding stage (the semi-batch stage) and the solid content of the final latex were critical to reducing the amount of coagulum.The monomer feeding of the second stage should start after monomer conversion 40% of the first stage and the solid content of the final latex should remain below 40%.Under such conditions little coagulum was observed.It was concluded that the two-stage semi-batch RAFT mini-emulsion polymerization was effective to synthesize higher molecular weight polymer (～8×104 g8226;mol-1) with narrow molecular weight distribution (PDI=～1.3) and low residues of the surfactant and co-stabilizer (～1.5%

mass).