Kinetic discussion on the catalysis of copper‐partially‐quaternized poly‐(vinylpyridine) complexes

Abstract

Abstract2,6‐Xylenol was oxidatively polymerized by Cu‐poly (vinylpyridine) (PVP) complex or Cu‐partially‐quaternized PVP (QPVP) complex in a homogeneous dimethylsulfoxide solution, and the mechanism of the catalysis of the polymeric Cu complexes was discussed. The polymerization rate increased in the following order: Cu‐pyridine <Cu‐PVP<Cu‐QPVP. The catalytic activity of the Cu‐QPVP complex exhibited a maximum in the region where the percentage of quaternization of QPVP was 20‐50% and tended to increase with the degree of polymerization of QPVP. Considering through the kinetic constants of the polymerization, the neutral salt effect, and the influence of the monomer species, it was cleared that the higher activity of the Cu‐QPVP catalyst was attributed to the electrostatic interaction between the QPVP complex and the anionic monomer. That is to say, the intermediate complex, to which xylenol is coordinated, is enthalpically stabilized due to the electrostatic field of the QPVP complex. Activation entropy ΔS† of the polymer catalyst was larger in comparison with the monomeric analog, and the larger ΔS†S was observed in the PVP system and the neutral‐salt‐added QPVP system, of which structures were compact. It is considered that the frequency factor of the dissociation step of the activated monomer increases because of the high density of cupric ion in the polymer complex.