Poly , photo-Fries

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). 

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. 

A thorough study of the photo-Fries rearrangement of poly(p-acetamido styrene) was made difficult by the lack of solubility of the polymer in solvents other than DMSO or DMF. Nevertheless, photoexposure of thin films of V cast from DMF solution confirmed the lack of reactivity of the polymer as only minimal conversions could be achieved even after long periods of exposure. 

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. 

The hydroxylated copolymers, poly(acenaphthylene-co-vinyl alcohol), were reacted with the following acyl chlorides 1-naphthoyl, 2-naphthoyl, benzoyl and cinnamoyl. The latter polymers contain an ester group as a spacer between the main chain and one of the fluorophores. The choice of an ester group as a connecting unit between the polymer chain and fluorophore is probably a poor one since it is known that carbonyl groups easily form triplets and photo-Fries rearrangements can occur (2). 

Quantum yield values measured in solution may not necessarily apply to polymer films, the usual environment for practical application of this photochemistry. McKean et al. have adapted the indicator dye method to the measurement of quantum yields for Bronsted acid photogeneration in poly-(4-tert-butoxycarbonyloxystyrene) [20], As with the solution photochemistry of diphenyliodonium salts [71], an inverse dependence of quantum yield on exposure intensity was observed absolute quantum yields from 0.26 to 0.40 were measured at 254 nm, which extrapolate to approximately 0.45 at zero intensity, comparable to the value estimated by Dektar and Hacker [82b] in solution. McKean et al. [20b] note that similar quantum yields in solution and polymer films below Tg have also been reported for photo-Fries rearrangements [84] and photodissociation of diacyl peroxides [85]. 

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. ... 

Miscellaneous Polymers - Soluble fluorescent extraction products from poly(acetylene) have been compared with those present in PVC. Photo-Fries rearran ments in the photodegradation of a Bis-Phenol-A poly(carbonate) are responsible for their stability. PTFE has been irradiated using high energy UV and found to give volatile fluorocarbons while photooxidation of poly(phenyl-ene) gives crosslinked and quinone methide products. A polyradical has been made based on poly(3,5-di-tert-butyl-4-[(2,4,6-tri-tert-butylphenyl)oxalato]phe-... 

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.

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... 

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] ... 

The photoyellowing of poly(4,4 -diphenylolpropane isophthalate) (4.58) has been attributed to a photo-Fries rearrangement in a polymer containing o-hydroxybenzophenone as part of the chain structure (4.59) [1391] ... 

Fluorenone based polyesters such as poly(9,9-bis(4-hydroxyphenyl) lluorene isophthalate) (4.61), poly(9,9-biscresol fluorene isophthalate) and poly(9,9-bis(3,5-dimethyl-4-hydroxyphenyl)fluorene isophthalate) undergo, under UV irradiation, typical photo-Fries rearrangement, during which linear o-hydroxybenzophenone moieties can be formed [1346] ... 

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. 

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. 

The mechanism is believed to be that of a photo-induced Fries rearrangement. It may be similar to one catalyzed by Lewis acids. Another example is a spontaneous rearrangement in the solid state of poly(cx-phenylethylisonitrile) [128] ... 

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