Structure–reactivity studies on the crosslinking of poly(vinyl methyl ether) in aqueous solutions: a pulse radiolysis study

Abstract

Pulse radiolysis techniques have been utilized to generate, characterize and study the kinetics of crosslinking reactions of the radicals of a temperature-sensitive polymer poly(vinyl methyl ether)(PVME) in aqueous solutions. The transient species formed on reaction with ˙OH has an absorption maximum at 310 nm with molar absorptivity (ε)= 1060 ± 330 dm³ mol^–1 cm^–1. The rate constant for the reaction of ˙OH with PVME has been determined as 3.2 × 10⁸ dm³ mol^–1 s^–1 by competition kinetics at 296 K. The decay profile of the transient species has been found to vary with the polymer concentration and/or dose rate indicating different modes of recombination under various conditions of irradiation. These results have been interpreted in terms of intra- and inter-molecular crosslinking reactions of polymer radicals and it has been shown that when the intramolecular crosslinking reaction predominates, the decay kinetics deviates from the classical second order and shows a time-dependent behaviour. Since the polymer undergoes a coil–globule transition above 307 K, the bimolecular rate constant for the reaction of ˙OH with the polymer and the decay kinetics of radicals formed have also been investigated at 318 K.