Photopolymerization reactions initiated by copper (II)–amino acid chelates: Investigation of the initiating species by flash photolysis. I

Flash photolysis of copper (II)–bis(amino acid) complexes (amino acids: glutamic acid, serine, or valine) in deaerated aqueous solution produces transient species having absorption maxima at around 350 nm. The transient species are identified as copper (II)–alkyl complexes. In the case of Cu(valine)2 at pH > 6.5 formation of Cu(II)‐alkyl complex is not observed; this is interpreted to be due to the presence of two bulky methyl groups of the coordinated valine ligand, which hinders the rearrangement. Pseudo‐first‐order rate constants for the decay of the transients are determined at different pH with varying concentration of amino acid ligand. The free‐radical species of the complexes responsible for the initiation of the vinyl polymerization reactions are identified as Cu(I)‐coordinated amino acid radicals which are formed in the primary photochemical reaction of the complex. A mechanism for the secondary reactions involving the initiating species consistent with the nature of the product formed and the pH dependence of the decay of the transients is proposed.