单体组成对甲基丙烯酸甲酯/丙烯酸丁酯RAFT共聚合转移常数的影响

采用Z基团为—CH2C6H5的RAFT试剂为链转移剂,AIBN为引发剂,60℃下进行甲基丙烯酸甲酯/丙烯酸丁酯(MMA/BA)的本体RAFT共聚合,并用GPC法测算不同单体组成下低聚物RAFT的链转移常数(Ctr).实验表明,对BA的均聚合,Ctr高达116,但对MMA的均聚合,Ctr约为0.1.在共聚体系中,Ctr与fMMA之间为非线性关系,随着fMMA的增加呈下降趋势.Ctr随单体组成的变化规律可以很好地解释不同单体组成下RAFT共聚合中分子量及其分布随转化率变化的规律.

INFLUENCE OF MONOMER COMPOSITION ON THE CHAIN TRANSFER COEFFICIENT IN METHYL METHACRYLATE/BUTYL ACRYLATE RAFT COPOLYMERIZATION

The bulk copolymerization of butyl acrylate (BA) and methyl methacrylate (MMA) in the presence of the RAFT agent with Z=—CH_2C_6H_5 and 2,2′-Azobis(isobutyronitrile)(AIBN) as an initiator was carried out at 60℃.The chain transfer coefficients (C_ tr ) at different monomer compositions were determined by the GPC peak resolution method.In the BA homopolymerization,C_ tr was up to 116 while it was about 0.1 in the MMA homopolymerization.Since C_ tr was too low,the homopolymerization of MMA mediated by the RAFT agent was out of control.In the copolymerization systems,C_ tr showed a nonlinear decrease with the increasing of MMA compositions.When a small fraction of BA was added to an MMA polymerization system,the polymerization became well controlled with PDI around 1.2 at the end of the polymerization.The changing trend of C_ tr with monomer compositions well explained the profiles of the molecular weight and its distribution against conversion with different monomer compositions.