PHOTOLYSIS OF COPOLYMERS 4-METHOXYACRYLOPHENONE WITH "2-HYDROXY-4-(2-METHACROYLOXYETHOXY) BENZOPHENONE

The photolysis of copolymers of 4-methoxyacrylophenone with 2-hydroxy-4-(2-methacroyloxyethoxy) benzophenone (4MAP/PBMA) containing 0-8 wt/wt 2% of BPMA was compared with that of poly-4-methoxyacrylophenone (P4MAP) in the presence of 2-hydroxy-4-(2-isobutyroyloxyethoxy) benzophenone (BPIB) in ethyl benzoate at 366 nm. In the photolysis of P4MAP proceeding through the long-lived triplet state, it was possible to separate quenching and screening effects of BPIB. The dependence of the ratio of quantum yields of main chain scission without and with quencher was linear for free quencher; for copolymerized quencher, however, the dependence indicated static quenching. Using the Perrin model for copolymers, the quenching sphere of 1.56 nm was calculated. Study of the emission decay of copolymers 4MAP/BPMA in poly(methyl methacrylate) films at 77 K give 1.86 nm for the quenching sphere. Similar values were found for quenching of 4-methoxyacrylophenone chromophore by built-in acceptors naphthalene and diphenyl (1.60 nm). These results indicate that energy transfer in carbonyl copolymers, both in dilute solution and in film, at 77 K proceeds at a distance a little greater than the sum of donor and acceptor diameters (about 1.2 nm) showing that the extent of triplet energy migration is limited. © 1979.