Laser and microsecond flash photolysis of 2-substituted anthraquinones and photochemical cross-linking of nylon 6,6 polymer

Abstract

Microsecond and nanosecond laser flash photolysis studies have been carried out on six 2-substituted anthraquinone compounds, namely the acrylamido, acryloxy, acetoylamino, benzoylamino, hydroxy and amino derivatives, and the data related to their photo-cross- linking activity in nylon 6,6 polymer. All the compounds give rise to triplet—triplet absorptions, with the benzoyl and acetoylamino derivatives showing the strongest absorptions followed by the acrylamido and acryloxy derivatives. Transient half-lives are found to be 7.0, 1.7, 0.7 and 0.63 μs for the acrylamido, acryloxy, benzoyl and acetoylamino derivatives respectively, which follow the order of their ability to induce photo-cross-linking of nylon 6,6 polymer, long triplet lifetimes being the more active. In the reductive solvent 2-propanol the triplet state of the 2-arylamido derivative is rapidly quenched owing to hydrogen atom abstraction. For both the acryloxy and acrylamido derivatives the first-order decay rates of the triplet state are found to be independent of the concentration of the ground state, suggesting that some degree of intramolecular interaction is involved between the side chain and the quinone carbonyl groups. In nylon 6,6 polymer, on the other hand, the acrylamido derivative gives a long-lived triplet—triplet absorption which decays to give a long-lived residual absorption with a maximum at 500 nm. The latter is associated with the formation of a radical anion species formed from a triplet exciplex involving the terminal amine end groups. On microsecond flash photolysis in 2-propanol the initiators give both semiquinone and radical anion absorptions formed by hydrogen atom and electron abstraction reactions, with the former being stronger for the acryloxy derivative.