Reaction Kinetics of Polymer Substituents Neighbouring-substituent Effects in Pairing Reactions

Abstract

Kinetic equations are derived for a model in which the probability of reaction involving a particular pair of polymer substituents depends on whether none, one or two of the adjacent pairs have already reacted. The extent f and rate f of reaction, and the number Nx of sequences containing x unreacted substituents, are given as functions of time for polymer molecules containing a finite number m of substituents, and for the asymptotic limit of infinite chains (m->oo). The reaction scheme is capable of showing autocatalytic (cooperative) or autoretardative behaviour depending on whether the reaction of a pair enhances or reduces the reactivity of neighbouring substituents. As far as we know there are no experimental data with which to test the general model, but the case where the neighbouring group effect is absent is model (I) analyzed previously. Experimental results for systems where there is evidence that model (I) may be obeyed are discussed, including the dehydration of poly(acrylic acid) and poly(methacrylic acid), the cyclization of rubber, the formalization of poly(vinyl alcohol), and reactions of poly(vinylidene chloride) and derivative polymers. Methods for analysing experimental data are also discussed.