Poly photo-Fries reaction

Fries rearrangement of aromatic formate esters suggests that phenols are the major products (.24) obtained in the reaction. As poly(p-hydroxystyrene) is remarkably clear in the deep UV, it is likely that poly(p-formyloxystyrene) will not suffer from the same problem of photostabilization upon exposure as was the case with poly (p-acetoxystyrene). This expectation was confirmed by our study of the photo-Fries reaction of p-cresyl formate no ortho rearranged product was isolated after reaction while p-cresol and a small amount of starting material were obtained. 

TABLE VI. Extinction coefficient of some products of the photo Fries reaction of poly 4-vinyl phenyl benzoate). Poly VB Poly (4-vinyl benzaldehyde) obtained by treating the copolymer with its dimethyl acetal by acidic solution. 

In the photoageing of polycarbonates, photo-oxidation has been shown to be a more important process than the photo-Fries reaction. The photo-oxidation of epoxy-resins has been found to depend on the type of hardener and its concentration. A correlation has been observed between the changes in chemical structure and thermally stimulated current of poly(vinyl alcohol) during photo-oxidation. Other studies of interest include the weathering of polymers outdoors,effect of ozonation on polymers, effect of drawing, effect of biodegradation, and changes in mechanical properties of thermoplastics. ... 

The photo-Fries reaction occurs readily in solid polymers and is observable in phenyl esters, particularly in poly(phenyl acrylate) and poly (phenyl methacrylate) and their derivatives. The course of the reaction can be followed very easily by ultraviolet spectroscopy, since the product hydroxy ketones have strong absorbance at 260 and 320 nm (Fig. 10). Reaction occurs with equal efficiency in small model compounds in solution and in the polymers in the solid phase (44). An Arrhenius plot of the quantum yield for the para product (Fig. 11) shows a linear increase up to 294 K, above which no further change in quantum efficiency is observed, either above or below the glass transition temperature. 

Figure 10. Absorption spectra of a PPA film after different periods of irradiation at room temperature, using light of wavelengths between 220 and 340 tun from an AEI medium-pressure mercury lamp. Reprinted with permission fiom S. K. L. Li and J. E. Guillet, Studies of the photo-Fries reaction in solid poly(phenylacrylate), Macromolecules, 10, 840 (1977). Ccpyright 1977, American Chemical Society.

Wang, Z., Holden, D. A., and McCourt, F. R W, Generation of nonrandom chromophore distributions by the photo-Fries reaction of 2-naphthyl acetate in poly(methyl methacrylate). Macromolecules, 23, 3773,1990. 

For the initial phase of the photo-Fries rearrangement, IA can be determined approximately by subtracting the absorption due to the strongest absorbing product of the reaction mixture, provided its concentration and molar extinction coefficient are known. By means of this initial rate approach Humphrey8 determined the quantum yields of the photorearrangement of 13 (913-14 = 0.14), of 14 (914-.18 = 0.056), and of poly-2,2-propanebis(4-phenyl carbonate) ([Pg.138]

A considerable amount of attention has also been paid to the photo-Fries rearrangement of polymer pendant groups. For example, the rearrangement of poly (phenyl acrylate) (10,11) in solution or in the solid-state, is usually incomplete and results in the formation of both the ortho and the para-hydroxyphenone rearranged products in amounts which vary with the conditions of the photolysis. A concurrent side-reaction, which we term the Fries degradation, also results in the liberation of small amounts of phenol (Scheme 2). Similar results have been obtained with poly (phenyl methacrylate) and other substituted aryl acrylates (4,9,12). 

No photo-Fries product was detected after UV irradiation in air. The cross-linking reaction occurs only in the absence of oxygen. The photo-oxidation reaction of poly(l,3-phenylene isophthalamide) is accompanied by a rapid chain scission [369] ... 

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). ... 

Gu, W. Q., Bi, S. G., and Weiss, R. G., 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, Photochem. PhotobioL Sci., 1, 52, 2002. 

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