Switchable Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization in Aqueous Solution, N,N-Dimethylacrylamide

Reversible addition-fragmentation chain transfer (RAFT) polymerization of a "more activated monomer" (MAM), N,N-dimethylacrylamide (DMAm), has been successfully achieved in aqueous solution using an acid/base switchable pyridyl-substituted dithiocarbamate RAFT agent. The effect of strength (pK(a)) and stoichiometry of the acid used to switch the RAFT agent on the molecular weight and dispersity of poly(N,N-dimethylacrylamide) (PDMAm) were examined, making use of high-throughput protocol. Best control was achieved with a stoichiometric amount of the strongest acid investigated, p-toluenesulfonic acid monohydrate. Use of weaker acids (higher pK(a)) or less than stoichiometric amounts of acid with respect to RAFT agent resulted in broader molecular weight distributions. These results can be rationalized in terms of the extent of protonation of the pyridine nitrogen of the RAFT agent (pK(a) similar to 3.13). The preparation of unimodal low dispersity block copolymers of PDMAm with the "less-activated" monomers (LAMs) N-vinylcarbazole (NVC), vinyl acetate (VAc), and N-vinylpyrrolidone (NVP) demonstrated the fidelity of the RAFT end group in these experiments and provides a further example of the utility of switchable RAFT polymerization.