Pulse radiolysis of sulphur compounds. Part 3.—Repair by hydrogen transfer of a macromolecule irradiated in aqueous solution

Abstract

Free radical repair by hydrogen transfer from a sulphydryl compound (cysteamine) has been extended to a polymeric system. Repair rate constants vary from 2.6 × 10⁷ M^–1 sec^–1 for ethylene glycol to 5 × 10⁶ M^–1 sec^–1 for polyethylene oxide (PEO) of molecular weight 20,000. The analysis of rate data for polymers of m.w. >200 is complicated by competing radical-radical reactions. A comprehensive reaction scheme is proposed and the kinetic equations solved numerically. The effects of pH and molecular weight on the repair rate have also been studied. Some further data on the pulse radiolysis of cysteamine solutions, including a determination of the extinction coefficient of the radical-ion RSSR^–(ε₄₁₀₀= 9.4 ± 0.5 × 10³ M^–1 cm^–1) are presented.