The kinetics of the oxidative polymerization of 2.6-xylenol with a copper-amine complex

It was found that the oxidative polymerization of 2.6-xylenol with a copper-amine complex proceeds via a mechanism similar to that of a MICHAELIS-MENTEN-type reaction, the steady state being maintained during the polymerization; the kinetics were studied. The LINEWEAVER-BURK plots showed linear relationships, supporting this mechanism. From the comparison of the kinetic constants it was concluded that oxygen not only takes part in the recycling step of the catalyst, but also promotes the catalytic action of the cuprous complex by being coordinated to the intermediate complex. K₁ values (the reciprocal of the MICHAELIS constant, K_m) vary with the amine-ligand species, but the reaction-rate constants (k₂) do not change, regardless of the ligands used. According to the kinetic formula, K₁ is proportional to the product of the formation constant of the complex between the copper-amine catalyst and the monomer (K′₁) by the rate constant of electron transfer (k_e). It is because of the K′₁ values that the apparent polymerization rate varies with the amine ligands in the region of relatively low monomer concentrations. It was found that, as the ligand ratio ([pyridine]/[Cu]) increases, i.e., as the selectivity for C? O coupling increases, the K₁ values become larger. The mechanism for the coupling selectivity is discussed in relation to the K₁ values.