The Effect of Ligand Molecular Weight on Copper Salt Catalyzed Oxidative Coupling Polymerization of 2,6-Dimethylphenol

Polyphenylene oxide (PPO) was prepared via oxidative coupling polymerization of 2,6-dimethylphenol (DMP) catalyzed by copper salt. The ligand was a novel series of random copolymers (PSVP) of styrene and 4-vinylpyridine prepared by reversible addition-fragmentation chain transfer (RAFT) copolymerization. The copolymers with well-controlled molecular weight (MW) were used to study the effects of ligand molecular weight on the catalytic activity and selectivity. It was found that the catalytic activity increased with the molecular weight but there existed an upper MW limit above which no further increase in activity could be achieved. With PSVP of F-vPy= 0.39, the critical MW was about 5000 g/mol. The mechanism involved in the successive complexation of copper ions and PSVP was elucidated and the equilibrium constants were estimated by pH titration. It was found that the macromolecular ligand was in favor of bridging Cu-II ions that formed catalytically active dinuclear copper-amine complexes. However, the catalytic selectivity was almost independent of the ligand MW. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3473-3481, 2010