Living radical polymerization. 1. The case of atom transfer radical polymerization of acrylamide in aqueous-based medium

Atom transfer radical polymerization (ATRP) of acrylamide has been carried out in water or in glycerol-water (1:1 v/v) medium at 130 degreesC using water-soluble initiators, viz. 2-chloropropionamide (2-Cl-PA) or 2-bromopropionamide (2-Br-PA) and CuX (X = Cl, Br) bipyridine complex as catalyst. Extraneous addition Of CuX2 (20 mol % of CuX) and/or excess X- ions (1 M alkali halide) in the reaction mixture helps to reduce molecular weight polydispersity (PDI). However, even under the best conditions (using both CuX2 and X- ion additives), the PDI is high, ca. 1.6-1.7. Also, the GPC traces show shoulders. The chain extension experiment, however, confirms the living nature of the polymers. Replacement of glycerol-water with water as the medium results in sluggish polymerization. The In M-0/M vs t plots are curved to start with but become linear after polymerization proceeds to variable extents depending on the additives used. The molecular weights tend to agree with the theoretical values as conversion increases. A method of selecting the appropriate ligand for ATRP has been proposed on the basis of the premise that a high rate of deactivation is one of the primary requirements for ATRP to succeed. A relative measure of the deactivation rate for various ligands has been obtained from the molecular weights (GPC) of polymers formed in a CuX2Lx deactivated polymerization initiated by an azo initiator at 90 degreesC. A ligand that leads to the highest deactivation rate has been proposed to be chosen.