Studies on immobilized polymer-bound imidazole-copper( ii) complexes as catalysts: 1. Oxidative coupling polymerization of 2,6-dimethylphenol catalysed by copper( ii) complexes of poly(styrene- co- N-vinylimidazole)

Abstract

The oxidative coupling polymerization of 2,6-dimethylphenol catalysed by copper( ii) complexes of poly(styrene- co- N-vinylimidazole) (Cu( ii)PS-Im) in toluene/isopropanol ( 13 2 v v ) was investigated. The electron paramagnetic resonance spectra of these complexes indicate that the complex had a mononuclear structure Cu(PSIm) 2+ 4 in solution for higher ligand/copper ratios. This mononuclear complex was found to be a more active catalyst for the reaction and more favourable for poly(2,6-dimethyl-1,4-phenylene oxide) formation than dinuclear complexes. Viscometric experiments on solutions of polymeric ligands with and without copper( ii) ions showed that the decreasing reaction rate for higher ligand/copper ratios may be due to too high concentrations of polymeric ligand, resulting in overlap of polymer coils. The effect of chain loading α with imidazole ligands on the catalytic activity showed an optimum value for α=0.11, which was explained predominantly in terms of strain in polymer chain segments between neighbouring ligand groups in the same copper complex. Michaelis-Menten kinetics were observed for the reaction under standard conditions with k 2=0.15s −1 and K −1 m=0.45dm 3mol −1. The smaller K −1 m for Cu( ii)PS-Im than for low-molar-mass copper( ii) complexes of N-methylimidazole (Cu( ii)NMIm) probably originates from steric hindrance of polymer backbone and difficult substitution of polydentate ligands by substrate. The transition to second order in copper indicates that dimerization of mononuclear Cu( i) complexes is necessary for reoxidation of Cu( i) to Cu( ii). Methanol as cosolvent appears to be more favourable for a higher K −1 m value than isopropanol in the case of Cu( ii)PS-Im as well as Cu( ii)NMIm.