Atom transfer radical polymerization of (meth)acrylamides

The polymerization of several (meth)acrylamides [N,N-dimethylacrylamide, N-tert-butylacrylamide, and N-(2-hydroxypropyl)methacrylamide] by atom transfer radical polymerization (ATRP) was attempted. When initiating systems containing Ligands commonly used in ATRP, such as linear amines or bipyridines, were employed, very low conversions were noticed in either bulk or solution, after more than 20 h at 90 degrees C. However, the use of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me(4)Cyclam) as a ligand provided polymers in high yields in a short time, but the polymerization was not controlled. This was attributed to the slow deactivation rate of the catalytic system. Experiments using model compounds for the active chain ends indicated that the low conversion obtained in the polymerization of (meth)acrylamides when linear amines or bipyridines are used as ligands may be explained by a slow activation in conjunction with a fast deactivation. The loss of bromine end groups during the polymerization through a cyclization reaction could have a contribution to the poor control in the ATRP of (meth)acrylamides. Additionally, poly(meth)acrylamides may competitively complex copper and form species with lower catalytic activity. Even though the ATRP of (meth)acrylamides was not a controlled process, by using the Me(4)Cyclam-based catalyst system and macroinitiators prepared by ATRP, poly(methyl acrylate-b-N,N-dimethylacrylamide) (M-n = 48 600, M-w/M-n = 1.33) and poly[butyl acrylate-b-N-(2-hydroxypropyl)methacrylamide] (M-n = 34 000, M-w/M-n = 1.69) block copolymers were synthesized.