Photo-Fries reactions polyesters

Equation 6 indicates that the solvent strength, 6, is pressure-dependent, providing a potential route to improved selectivity and rate by "pressure-tuning the solvent. A number of attempts to demonstrate reactivity control in su rcritical CO2 for Diels-Alder (75-77) and organic photoreactions (78,79) have exhibited very small effects. Andrew and coworkers have recently demonstrated dramatic solvent cage effects on selectivity of a photo-Fries reaction close to the critical density.(80) More polar SCF s have shown more promising results control of esterification rates and polyester molecular weight distribution via enzymatic catalysis in fluoroform has been demonstrated. (81,82)... 

It has been shown (122) that aromatic polyesters degrade by a combination of Norrish I and Norrish II photolyses, with photo-oxidation playing an important part. Aromatic esters may also undergo an important photochemical reaction, known as the photo-Fries rearrangement (123). 

Another field of application is the design of polymeric imaging systems. The lithographic potential of a photochemical reaction is based on the possibility of dissolving selectively either the exposed or the unexposed areas of a polymer film. Because aU the photo-Fries products are phenols, the irradiated polyester should be easily dissolved in aqueous base, while the unchanged starting material should remain undissolved. The key photochemical step of this sequence is shown above for the conversion of poly(p-acetoxystyrene) (34) into (35) (Scheme 9). ... 

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