Small heterocyclic ligands improve the copper-catalyzed oxidative coupling of 2,6-dimethylphenol to poly(2,6-dimethyl-1,4-phenylene ether) Original Research Article

Poly(2,6-dimethyl-1,4-phenylene ether) (PPE) [J. Polym. Sci. A 36 (1998) 505], which is widely used in high-performance engineering plastics, is obtained by the copper-catalyzed oxidative coupling of 2,6-dimethylphenol. The oxidative polymerizations have been carried out in acetonitrile with copper-imidazole complexes as the catalyst precursor compounds, which appeared to be extremely active. Different substituents on the imidazole ring showed that both the ligand basicity and the steric hindrance close to the coordinated nitrogen atom are important factors to increase the catalytic activity. Higher activities are always found with an excess of ligand and when using monodentate ligands instead of didentate ones. Most likely, the imidazole moieties may also act as base. Another nitrogen donor ligand, viz. 2-methyl-oxazoline, has been successfully tested, showing a very good activity in this oxidative coupling reaction.