STUDIES ON IMMOBILIZED POLYMER-BOUND IMIDAZOLE COPPER(II) COMPLEXES AS CATALYSTS .2. IMMOBILIZATION OF COPPER(II) COMPLEXES OF POLY(STYRENE-CO-N-VINYLIMIDAZOLE) BY QUATERNIZATION OR ADSORPTION ON SILICA AND THEIR CATALYZES OF OXIDATIVE COUPLING OF 2,6-DISUBSTITUTED PHENOLS

Copper(II) complexes of poly(styrene-co-N-vinylimidazole) (Cu(II)-PS-im) were immobilized on modified silica by quaternization or on unmodified silica by adsorption and these immobilized polymer-bound complexes were applied as catalysts for oxidative coupling polymerization of 2,6-dimethylphenol (DMP) in toluene/methanol (13/2 v/v). Higher average chain loading (α) of PS-im with imidazole groups, e.g. α ≥ 17%, was essential for successful adsorption. A main role of hydroxide appears to be production of more reactive phenolate anions from DMP. A rise in reaction rate was not observed for high ligand/Cu, which probably resulted from too high viscosity of the silica suspension at high ligand/Cu. In a batch process under comparable conditions both types of immobilized polymer catalysts were found to have the same preference for poly-2,6-dimethyl-1,4-phenyleneoxide formation as non-immobilized Cu(II)-PS-im and their low molar mass analogue. However, they were five times less active than non-immobilized ones, which was explained primarily in terms of a reduced effective ligand/Cu ratio after the immobilization of polymeric ligands.