OXIDATIVE COUPLING POLYMERIZATION OF 2,6-DIMETHYLPHENOL CATALYZED BY COPPER(II) COMPLEXES OF N-METHYLIMIDAZOLE

The oxidative coupling polymerization of 2,6-dimethylphenol (DMP) catalysed by copper(II) complexes of N-methylimidazole in toluene/iso-propanol (13/2 v/v) or 1,2-dichlorobenzene/methanol (ODCB/MeOH) (13/2 v/v) was investigated. EPR spectra of these complexes indicated that the complex had a mononuclear structure in solution for higher ligand/copper ratios. The mononuclear complex was found to be a more active catalyst for the reaction and more favourable for poly(2,6-dimethyl-1,4-phenyleneoxide) (PPO) formation than dinuclear complexes. A main role of hydroxide appears to be to give more reactive phenolate anions from DMP. In toluene/iso-propanol, Michaelis-Menten kinetics were observed for the reaction under standard conditions with k2 = 0.15 sec-1 and Km-1 = 9.1 dm3 · mol-1. Also, a better catalytic specificity for PPO formation and a higher molar mass of PPO (Mn = 78,300) were obtained in toluene/iso-propanol than in ODCB/MeOH. At reaction temperatures of 5-25° in toluene/iso-propanol, a yield of only 0.8-1.0% of the side product DPQ was achieved by adding the DMP solution slowly to the reacting system. © 1990.