Hydroxyl-radical-induced reactions of the poly(vinyl methyl ether) model 2,4-dimethoxypentane in the absence and presence of dioxygen: a pulse radiolysis and product study

Abstract

Hydroxyl radicals were generated radiolytically and reacted with 2,4-dimethoxypentane, a low-molecular-weight model of poly(vinyl methyl ether). Using the pulse radiolysis technique and specific radical scavengers, it has been shown that OH radicals react by H-abstraction (k = 3.7 × 10⁹ dm³ mol⁻¹ s⁻¹), generating primary (4, ≈45%) and tertiary (2, ≈35%) α-alkoxyalkyl radicals as well as secondary and primary β-alkoxyalkyl radicals (3 and 1). In the absence of dioxygen, radicals 1–4 decay (2k = 1 × 10⁹ dm³ mol⁻¹ s⁻¹) by recombination and disproportionation yielding dimers and vinyl ethers in nearly equal amounts. In the presence of dioxygen, four different peroxyl radicals (5–8) are formed. They decay bimolecularly by non-uniform kinetics (initially, 2k ≈ 7 × 10⁷ dm³ mol⁻¹ s⁻¹). Especially at low dose rate, they also undergo (mainly) intramolecular H-abstraction. This leads to an increased autoxidation, e.g. dioxygen uptake reaches values more than three-times the initial radical yield. Based on these data, the major reaction pathways as well as some side- and consecutive reactions are discussed.