RAFT聚合合成高分子量嵌段聚合物

以合成高分子量聚合物为目标,以苯基二硫代乙酸-1-苯基乙酯(PEPDTA)作为RAFT试剂,研究引发剂的种类(偶氮二异丁腈(AIBN)、1-1′-偶氮环己腈(ACC))、用量及聚合温度对苯乙烯/丙烯酸丁酯RAFT共聚合过程和聚合物结构的影响.结果发现,由于体系中RAFT浓度很低,相应的引发剂浓度要比传统自由基聚合低得多,只有采用较高的聚合温度和低分解速率常数的引发剂(ACC),才能制得无活性聚合物分率低(<0.1)、分子量高的聚合物,并进一步得到杂质含量少、分子量分布窄的嵌段聚合物.

THE SYNTHESIS OF HIGH MOLECULAR WEIGHT BLOCK COPOLYMERS BY RAFT POLYMERIZATION

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 5×10~4 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.