Pulse radiolysis of poly(vinyl methyl ether) in aqueous solution. Formation and structure of primary radicals

Abstract

The reactivity of a temperature-sensitive polymer poly(vinyl methyl ether) (PVME) towards • OH , e − aq, and H • atoms in aqueous solution has been investigated by pulse radiolysis. The rate constant for reaction of • OH with PVME (1.2 × 10 5 Da) has been determined as 2.2 × 10 8 dm 3 mol −1 s −1 by competition kinetics at 296 K. Hydrogen atoms are less reactive. The rate constant of the reaction of hydrated electrons with PVME is lower than 1.9 × 10 7 dm 3 mol −1 s −1. Radicals of PVME formed in the reaction with • OH have a featureless absorption spectrum with increasing absorption towards shorter wavelengths. Upon • OH attack three kinds of radicals are generated: two at different α-positions and one at a β-position with respect to the oxygen atom. The α-radicals rapidly reduce tetranitromethane yielding the stable nitroform anion. From the yield of the latter species it is calculated that ca. 54% of the PVME radicals are formed at α-positions. Results are compared with earlier data on low-molecular-weight ethers and simple water-soluble polymers.