Photo-fries rearrangements of 1-naphthyl esters in the glassy and melted states of poly(vinyl acetate). Comparisons with reactions in less polar polymers and low-viscosity solvents.
The photo-Fries and associated photoreactions of four 1-naphthyl acylates have been examined in two types of poly(vinyl acetate) (PVAc) films above and below their glass transition temperatures, Tg. Because of the 'templating' effect of the esters on their reaction cavities, especially below Tg, the distributions of photo-Fries products, as mandated by the intermediate acyl/1-naphthyloxyl singlet radical pairs, are determined largely by the initial conformations of the guest molecules. Even above Tg, at 50 degrees C, where segmental chain motions of PVAc are relatively rapid, the influence of the cages in directing product formation is apparent. The radical-pair recombination rates for formation of the keto precursor of 2-(2-phenylpropanoyl)-1-naphthol upon irradiation of 1-naphthyl 2-phenylpropanoate in PVAc are reduced drastically as the temperature is lowered from above to below Tg. Comparison of results in PVAc with those in low-viscosity solvents (ethyl acetate and hexane) and low-polarity polymer films (polyethylene and polypropylene) indicate that interactions between the radicals produced from irradiation of 1 and the acetate pendant groups of PVAc, as well as the nature of its chain motions above and below Tg, influence enormously the course of the photo-Fries rearrangements.
Gu
Weiqiang
W
Department of Chemistry, Georgetown University, Washington, DC 20057-1227, USA.
Bi
Shuguang
S
Weiss
Richard G
RG