Phenyl‐2,4,6‐trimethylbenzoylphosphinates as water‐soluble photoinitiators. Generation and reactivity of OṖ(C6H5)(O−) radical anions

Abstract

Lithium‐ and magnesium phenyl‐2,4,6‐trimethylbenzoylphosphinates (TMPPL and TMPPM) are effective water‐soluble photoinitiators for the free‐radical polymerization of appropriate monomers such as acrylamide (AA) and methacrylamide (MAA) in aqueous solution. They are also capable of initiating the polymerization of other olefinic compounds such as styrene (St), methyl methacrylate (MMA) or acrylonitrile (AN) in water‐containing solvent mixtures such as 1:1 water‐acetonitrile mixtures. This is due to the fact that TMPPL and TMPPM undergo α‐scission with a rather high quantum yield (ϕ(α) ≈ 0,35) resulting in the formation of 2,4,6‐trimethylbenzoyl radicals and OṖ (C 6 H 5)(O−) radical anions. The latter are very reactive toward olefinic monomers. Bimolecular rate constants kR+M/(L/(mol · s)) were determined by flash photolysis at room temperature, e. g. in neat water: 3,8 · 10 8 (MAA), 2,2 · 10 8 (AA), and in H 2 O/CH 3 CN (1:1, v/v): 1,8 · 10 7 (St), 1,2 · 10 8 (MMA), 8,4 · 10 7 (AN).