Poly phenyl acrylate

Under UV irradiation of poly(phenyl acrylate) (3.44), the photo-Fries rearrangement to polymeric ortho- 3.45) and para-(3.46) hydroxybenzophenones occurs [874, 1333]  

These course of the reaction can be followed very easily by UV/VIS spectroscopy since the hydroxy ketone products have strong absorbance at 260 and 320 nm (Fig. 3.27). Reaction occurs with equal efficiency in small model compounds in solution and in the polymers in the solid phase [1333]. 

This reaction is probably less important in producing CH3 radicals. 

All these processes have been proved by ESR spectroscopy which shows existence of the radicals formed from [340, 665, 980,1471,1472, 2114, 2116, 2292]  

Main chain scission producing the scission type radicals, which give a well-known nine-line ESR spectrum. 

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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). 

Bisjak, C.R et al. Novel monolithic poly(phenyl acrylate-co-l,4-phenylene diacrylate) capillary columns for biopolymer chromatography. J. Chromatogr. A. 2007, 1147,... 

Poly(phenyl acrylate) Poly(methyl methacrylate) (atactic) 57 105 — Poly(/>-xylene) 375... 

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. 

Salicylate-type additives are largely imsuitable for use in aromatic polyesters, but some UV-stabilising ability has been shown by polyesters which contain moieties capable of transformation in the same way as the salicylates the so-called Photo-Fries rearrangement [20-22]. More recently, re-arrangeable polymers such as poly(phenyl acrylate) and poly(p-methylphenyl acrylate) have been proposed... 

Second virial coefficient of poly(phenyl acrylate)... 

Fig. 3.27. Ultraviolet absorption spectra of a poly(phenyl acrylate) film after different times of UV irradiation at room temperature [874]. (Reprinted with permission from [874]. Copyright (1984) American Chemical Society.)...

The mechanisms illustrated above are dependent on the physical state of the material, in contrast to the behaviour of poly(phenyl acrylate) when irradiated around 310 nm. A systematic study of the phot-Fries rearrangement in both solid and solution yielded the result that the quantum yield for the reaction was independent of the state of the substrate. This observation was accounted for by the proposal that the rearrangement requires almost zero free-volume and proceeds as a caged radical mechanism (Scheme 15). 

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