Atom transfer radical polymerization of 1,3-butadiene using novel CuBr/pyridine-2-carboxamide catalysts

Atom transfer radical polymerization (ATRP) is one of the most successful methods to polymerize styrenes, (meth)acrylates, and a variety of other monomers in a controlled fashion. Novel ligands, 4-alkyl pyridine-2-carboxamides [R = methyl (4a), t-butyl (4b), H (4c)], have been prepared through the reaction of 4-alkyl-2-cyanopyridine with water in the presence of 0.4 mol% of base in ethanol solution. The living free radical polymerization of 1,3-butadiene was facile in the presence of the CuBr/4a catalytic system. Several effects, such as those of the ligand, solvent, and temperature, and a kinetic study of the ATRP of 1,3-butadiene (BD), were studied systematically. The optimum conditions for the ATRP of BD were [CuBr]_o/[4a]_o/[PEBr] _o/[BD]_o = 1:2:1:100 at 80°C in veratrole solution (w/w= 1:2); these conditions yielded well-defined polybutadiene (PBD) with a narrow molecular weight distribution (1.40).