Room-Temperature RAFT Polymerization via Redox Initiation
From both academic and industrial standpoint, the ability to conduct living free radical polymerizations at room temperature is clearly a desirable feature. It is especially important for the monomers highly susceptible to temperature. Reversible addition fragmentation chain transfer (RAFT) polymerization shows particular promise because it possesses more advantages such as using a variety of monomers, performing under various conditions, and preparing polymers with various architectures including block, graft, and star copolymers. Recently, we have found that RAFT polymerizations of vinyl monomers proceed very well at room temperature in bulk, organic or aqueous media using the traditional redox systems, benzoyl peroxide(BPO)- N,N-dimethylaniline(DMA) and potassium persulfate(PPS)-sodium thiosulfate(STS), as initiators respectively. In Figure 1(a) and Figure 2(a), it can be seen that molecular weight of the polymer increases linearly with monomer conversion and that molecular weight distribution remains very narrow in the polymerization except in the range of low conversion and becomes narrower with monomer conversion increasing. A linear relationship between ln([M]0/[M]) and polymerization time can be observed in Figure 1(b) and Figure 2(b), which indicates that the polymerization is a first order reaction with respect to monomer concentration and that the number of active radicals remains constant during the polymerization.All the evidence demonstrates that the cheap conventional redox initiators are very efficient for the room temperature RAFT polymerization and the processes reveal good features of living radical polymerization.
