RAFT (Co)Polymerization Of Methyl Methylacryalte In Miniemulsion

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the newest developed living/controlled free radical polymerization techniques. Compared with other living/controlled free radical polymerization methods, major advantages of the RAFT polymerization are i) easy transplant based on prescription and processes of traditional free radical polymerization ii) suitability with a very wide variety of monomers iii) higher polymerization rate. The objective of this work mainly focused on RAFT polymerization in miniemulsion.First, two RAFT agents with great different transfer coefficients, 1-phenylethyl phenyldithioacetate (PEPDTA) and 2-cyranoprop-2-yl dithiobenzoate (CPDB), were synthesized and their structures were confirmed by 1H NMR and 13C NMR. In order to select proper polymerization system for study, the selectivity to the monomers of the two RAFT agents was investigated. MMA homopolymerization with CPDB in miniemulsion and MMA/St copolymerization with PEPDTA in miniemulsion were further studied in this work.Then MMA polymerization with CPDB in miniemulsion and in bulk were both investigated. Polymerization rate in minemulsion is much faster than that in bulk for the compartmentalization effect in miniemulsion. In both systems, the development of number average molecular weight(Mn) and its distribution(PDI) is the same. As the conversion increases, Mn linearly increases and PDI first decreases to a minimum then sharply increases in the late stage. Because the reaction of the polymeric RAFT agent was controlled by diffusion in the late stage of polymerization, PDI became rather broad.The polymerization was then extended to copolymerization of MMA/St in miniemulsion with PEPDTA. St polymerization with PEPDTA can be well controlled, and MMA polymerization with PEPDTA cannot be controlled. However, in the MMA/St copolymerization system, Mn linearly increases with the increase of conversion, which indicates that the copolymerization can be well controlled. In the copolymerization process, the development of PDI with the conversion is dependent on the ratio of MMA to St. When the amount of MMA is dominant, PDI decreases first and then increases with the increase of the conversion. But when the amount of St is dominant, PDI increases first and then decreases. And in the case of MMA:St=9:1 (molar ratio), in the late stage of polymerization, the difference of PDI is very large between the results calculated by RI signal and calculated by UV signal. The reason is that in the late stage, St is nearly consumed, the residual MMApolymerization is not under control to form a high molecular weight shoulder and make the PDI very high. Also coupled termination events contributed some to the shoulder peak. After the conversion of the copolymerization reach 100%, pure St was continuously added by semibatch and well-defined A-C block copolymer was obtained.