Small heterocyclic ligands improve the copper-catalyzed oxidative couplingof 2,6-dimethylphenol to poly(2,6-dimethyl-1,4-phenylene ether)

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 obtain ed by the copper-catalyzed oxidative coupling of 2,6-dimethylphenol. The ox idative polymerizations have been carried out in acetonitrile with copper-i midazole complexes as the catalyst precursor compounds, which appeared to b e extremely active. Different substituents on the imidazole ring showed tha t both the ligand basicity and the steric hindrance close to the coordinate d nitrogen atom are important factors to increase the catalytic activity. H igher activities are always found with an excess of ligand and when using m onodentate ligands instead of didentate ones. Most likely, the imidazole mo ieties may also act as base. Another nitrogen donor ligand, viz. 2-methyl-o xazoline, has been successfully tested, showing a very good activity in thi s oxidative coupling reaction. (C) 2001 Elsevier Science B.V. All rights re served.