Reversible Addition Fragmentation Chain Transfer Polymerization Using Novel Benzoimidazole Dithiocarbamates As RAFT Agent

Three novel RAFT agents, 2-nonyl-benzoimidazole-1-carbodithioic acid benzyl ester (1a) , 2-methyl-benzoimidazole-1-carbodithioic acid benzyl ester (1b), and 2-phenyl-benzoimidazole-1-carbodithioic acid benzyl ester (1c) were synthesized and successfully used in the RAFT polymerization of styrene in bulk with thermal initiation.It was found that the polymerization of styrene could be well controlled in the presence of 1a or 1b or 1c. The linear relationships between ln([M]₀/[M]) and polymerization time indicated that the polymerizations were first-order reactions with respect to monomer concentration. The molecular weights increased linearly with monomer conversion and were close to the theoretical values. The molecular weight distributions (M_w/M_n) were very narrow from 5.3% conversion up to 94% conversion ( M_w/M_n < 1.3; 1b or 1c as RAFT agent). Compared with 1b and 1c, the control of 1a over the polymerization was more effective (M_w/M_n < 1.1). The molecular weights (Mn) obtained from gel permeation chromatographic (GPC) were close to the theoretical values (Mn,th) and the M_w/M_ns were relatively narrow up to high conversion in all cases. It was confirmed by chain extension reaction that thermal initiated polymerization of styrene using 1a or 1b or 1c as RAFT agent was well controlled in the RAFT mechanism. The effects of polymerization temperatures and the molar ratio of styrene to RAFT agent on the polymerization were investigated. It was found that the rate of polymerization in case of 1a or 1b or 1c was almost same at the same polymerization temperature, and increased with increasing the polymerization temperature. At high ratio of [styrene]₀ : [RAFT agent]₀ , the polymerizations were not well controlled and the molecular weight distribution (M_w/M_n) became broad.In summary, following conclusions were made: the reversible addition fragmentation chain transfer polymerizations of styrene using benzoimidazole dithiocarbamates as RAFT agents showed controlled free radical characters with well controlled molecular weight, narrow polydispersity and linear relationship between...