On the reactivity of phosphonyl radicals towards olefinic compounds

Abstract

Abstract Phosphonyl radicals of the structure OṖR 1 (R 2 ) with R 1 and R 2 : C 6 H 5 ( 1 ); C 6 H 5 , OCH(CH 3 ) 2 ( 2 ); CH 3 , OCH 3 ( 4 ) and OC 2 H 5 ( 5 ) were generated by UV‐photolysis of appropriate acylphosphine oxides or acylphosphonates which are effective initiators of the free radical polymerization of olefinic compounds. All five radicals are very reactive towards monomers such as methacrylonitrile, styrene and methyl methacrylate ( k = 5 · 10 7 to 2 · 10 8 1 · mol −1 · s −1 ), as was found by employing laser flash photolysis techniques. In the cases of acrylonitrile, methyl acrylate, butyl vinyl ether, and vinyl acetate k ranged from 10 6 –10 7 1 · mol −1 · s −1 . The high reactivity of the radicals 1 – 5 is due to their tetrahedral structure. The Q‐e scheme of Alfrey and Price proved useful to recognize trends in the dependence of k on the chemical nature of both phosphonyl radicals and monomers.