Atom transfer radical polymerization of N,N-dimethylacrylamide

The polymerization of N,N-dimethylacrylamide (DMA) under atom transfer radi cal polymerization (ATRP) conditions was studied. The ligand, solvent (wate r, n-butanol, and toluene), initiator, and Cu halide were varied. High mono mer conversions were obtained using the Me(4)Cyclam ligand. Polymerizations in water that were initiated at room temperature were complete within minu tes. However, none of the experimental conditions produced a controlled pol ymerization. This conclusion is based on broad molecular weight distributio ns, poor agreement between theoretical and experimental M-n, incremental mo nomer addition experiments, and end group analysis. We believe that the Cu salts complex to the amide group of the chain ends and stabilize the radica l. This stabilization retards the deactivation step in ATRP and produces an unacceptably high concentration of radicals which leads to spontaneous ter mination reactions. In addition, we have indirect evidence for a cyclizatio n reaction involving nucleophilic Br displacement by the penultimate amide nitrogen; this cyclic onium intermediate undergoes hydrolysis to form a hyd roxy-terminated polymer.