Quaternization of poly(4-vinyl pyridine). Kinetic and viscometric measurements

Abstract

Quaternization reactions of poly(4-vinyl pyridine) with n-alkyl bromides in propylene carbonate as solvent have been carried out, with and without added low molecular weight pyridinium salts, to give a comparison under these conditions of reaction kinetics, viscosities of reacting mixtures and cloud-point temperatures, where relevant. There is no primary salt effect on the kinetics; the kinetic behaviour is virtually unaltered by salt, i.e., the neighbouring-group retardation is preserved, except that in some cases the salt induces eventual clouding of the reacting system and extreme retardation of the reaction; the viscosity of a reacting system expressed as a reduced viscosity (viscosity number) passes through a maximum in the absence of salt, but this is suppressed when salt is present. The observations are explained mainly on the basis of a neighbouring-group effect involving steric hindrance, and a global effect where polymer molecules initially expand during reaction, and then contract as the solvent quality diminishes. Addition of salt prevents coil expansion and induces salting out; there could also be binding of the salt to the polymer.