Radiation-induced, solid-state polymerization of derivatives of methacrylic acid. IX. Electron spin resonance and product analysis study of the gamma radiolysis of methacrylic acid, barium methacrylate and their saturated analogues, isobutyric acid and barium isobutyrate

Abstract

Methacrylic acid and barium methacrylate polymerize in the solid state during and after gamma irradiation. Previous ESR studies have indicated a free radical chain mechanism initiated by radical, particularly H atom, addition to the C=C bond. The radiation chemical yields of small molecular products are now reported and correlated with the ESR spectra and yields of molecular products from the saturated analogues, isobutyric acid and barium isobutyrate, in order to provide a detailed mechanism for the radiolysis. The ESR spectrum of barium isobutyrate at -196°C was similar to that of isobutyric acid and is attributed to (i) isobutyrate radical CH 3-Ċ(CH 3)COO -; (ii) isobutyrate anion radical [CH 3-CH(CH 3)COO -] -; and (iii) isopropyl radical CH 3-Ċ(CH 3)H. Conversion of radicals (ii) and (iii) into (i) occurred on warming and second-order decay of (i) was measured at higher temperatures. For isobutyric acid irradiated at 0°C, G(CO 2)=5.4, which is compatible with values for n-carboxylic acids, but in marked disagreement with G(CO 2)=14.4 for isobutyric acid reported by Johnsen. (11) Water was proven to be a significant radiolysis product. CO 2 was the major product from methacrylic acid and barium methacrylate, but in lower yields than from the isobutyrates; the other products were propyne, hydrogen, water, propylene, carbon monoxide and methane, all in relatively low yield.