Photo-Fries rearrangement polymers

The radiation induced side-chain modification of polymers containing pendant phenyl ester groups has been the object of several studies as some undergo a photo-Fries rearrangement (JJ while others such as... 

The present work deals with the photo-Fries rearrangement (PFR) and covers the literature appearing since the first report of Anderson and Reese to the beginning of 2002. It includes both the mechanistic aspects and the synthetic applications of this reaction. The topic of the PFR in polymers is also treated. In addition, a section has been devoted to the photo-Fries rearrangement in organized media, a field of recent interest. 

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). 

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. 

Blends of iso- and terephthalates give amorphous, transparent resins, mosdy yellow in color. Heat-deflection temperatures are higher than those of 100% PC resins and depend on the iso- to terephthalate ratio. For example, a resin with a 1 1 ratio has a value of 160°C. These resins are flame retardant mechanical and electrical properties are similar to those of PC resins. The notched Izod impacts are lower at 150—300 J/m (4.7—5.6 fflbf/in.), even in thick sections. Long-term uv radiation stabilities are excellent, but yellowness increases during initial exposure owing to photo-Fries rearrangements (80), wherein 0-hydroxy-benzophenone units are produced along the polymer chains. 

Irradiation (313 nm) of films of polymers such as 1 leads to UV-Vis, IR, and solid-state 13C nmr changes attributed to a combination of 2 + 2 photocycloaddition and photo-Fries rearrangement [21], the latter presumably leading to cinna-moylphenol moieties, 2, in the irradiated polymer. Films irradiated at 313 nm in... 

The photo-Fries rearrangement of polymers such as 1 leads to yellowing, an undesirable behavior for many potential applications. The photochemistry of analogous MCLC polymers has been reported [30] in which the alkoxyphenyl ester groups of 1 have been replaced by 4,4 -franj-disubstituted cyclohexyl... 

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). 

The photo-Fries rearrangement of polymers containing phenyl formate units (e.g. the polymer derived from para-formyloxystyrene) has been examined. 

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]. 

The effects that initiator derived residues and functional groups have on polymer properties is an area that needs further study. For example, as discussed above, benzoyl peroxide leads to the formation of benzoyloxyphenyl groups in PS. It is known that the polymerization of p-benzoyloxystyrene [155] and its copolymerization with styrene [156] leads to the formation of photo-reactive polymers. Upon irradiation these polymers undergo a facile photo-Fries Rearrangement resulting in the conversion of the benzoyloxyphenyl groups to hydroxybenzophenone moieties [157]. Other side reactions also lead to the formation of phenolic groups and free benzoyloxy radicals [155]. 

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