RAFT polymerization is a type of psudo_living radical polymerization.In order to synthesize high pure block copolymers by RAFT polymerization

it is desirable to suppress the irreversible termination which may result in the formation of dead chains.For polymers less than 5×104 g/mol

the dead chain fraction could remain to be lower than 0.1 by reducing the initiator concentration.In the synthesis of block copolymers

the dead chains formed in the first stage are actually contaminant.Targeting to the synthesis of high pure block copolymers with high molecular weight using RAFT polymerization

we studied the copolymerization of butyl acrylate and styrene mediated by 1_phenylethyl phenyl_dithioacetate (PEPDTA) as a RAFT agent.The influences of the type of initiators (AIBN (2-2′-azobis(isobutyronitrile))

ACC(1-1′-azobis(cyclohexane_carbonitrile))

the concentrations of initiator and polymerization temperature on the copolymerization kinetics and molecular weight and its distribution were investigated.When AIBN was used

the polymerization would stop at middle monomer conversion

which limited the increase of molecular weight of the copolymer if we reduced the initiator concentration.It was found that only with the initiator (ACC) with small decomposition rate constant and high polymerization temperature

the block copolymer with high molecular weight and small fraction of dead chains (0.1) could be synthesized.The reason for these quite strict requirements is that the initiator concentration should remain far below that of the conventional radical polymerization

which is limited by the very low RAFT concentration.