枯基醇/三氟化硼在含水介质中引发苯乙烯可控正离子聚合的研究

研究了含水介质中,以枯基醇(CumOH)/三氟化硼(BF3)为引发体系的苯乙烯正离子聚合的特征,探讨了CumOH用量、体系中的水含量对苯乙烯正离子聚合转化率、聚合速率以及产物分子量及其分布的影响;并从分子模拟、分子量末端结构等角度探讨含水介质中苯乙烯正离子聚合的反应机理.结果表明,H2O]≤0.11 mol/L条件下,苯乙烯正离子聚合具有可控聚合的特征;水对聚合速率、单体转化率以及分子量影响较小;H2O]>0.11 mol/L,正离子聚合不能顺利进行.根据计算结果,CumOH/BF3引发体系相对于CumOH/H2O引发体系在参与引发所需要的活化能垒更小,说明CumOH/BF3更容易引发苯乙烯正离子聚合,这与实验结果一致.CumOH/BF3引发体系是通过活化C—O键来引发苯乙烯正离子聚合,水作为可逆终止剂有利于进行可控聚合,并得到了末端含有羟基的聚合物.

STUDY ON CONTROLLED CARBOCATIONIC POLYMERIZATION OF STYRENE WITH CumOH/BF_3 INITIATING SYSTEM IN PRESENCE OF WATER

The styrene cationic polymerization with the CumOH/BF3 initiating system in presence of water was studied.The effects of concentrations of CumOH and water on monomer conversion,polymerization rate and molecular weight of polystyrene were also investigated.An exhaustive mechanistic study of the styrene cationic polymerization in presence of water was proposed by molecular simulation and analyzing terminal structure.It is found that cationic polymerization of styrene exhibits controlled characteristic when ≤ 0.11 mol/L;the content of water in solvent has no significant influence on rate of polymerization reaction,the conversion of monomer and molecular weight.However,cationic polymerization cannot be processed under a high excess of water( > 0.11 mol/L).On the basis of calculation results of activation energy,CumOH/BF3 initiating reaction is easier to proceed comparing with CumOH/H2O initiating reaction,which is found to be in line with the experimental results.The initiation reaction of CumOH/BF3 proceeds via activation of C—O bond of ComOH to give active spieces.The water may serve here as a reversible chain transfer agent not only providing control over the polymerization reaction,but also forming hydroxy terminal groups.