Photo-Fries reactions polycarbonates

For polycarbonate the main photolytic reaction is the photo-Fries reaction (see Scheme 2). For this polymer the main questions are How important is the photo-Fries reaction and if it plays a role does it form free radicals that initiate the oxidation of the polymer ... 

Scheme 2. Photo-Fries reaction of Bisphenol A Polycarbonate.

The chemical processes involved in polycarbonate photodegradation are not well defined. Much early work concentrated on the photo-Fries reaction, which involves rearrangement to... 

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. ... 

Fukuda and Osawa [104] studied the photodegradation of polycarbonate films in air using the IR absorbance band at 1687 cm to monitor the photo-Fries reaction products. Only the short wavelengths of X = 260 and 280 nm showed any product formation longer wavelengths yielded no measurable... 

Photolytic decomposition of polycarbonate films was shown to produce products that are also consistent with the photo-Fries reaction. These are salicylic acid and bisphenol type species [580]. This is in agreement with earlier studies that showed that a variety of processes, including rearrangements (photo-Fries) and photo-oxidation, can occur when bisphenol A-based polycarbonate is photolyzed [581, 582]. 

Pickett JE. Influence of photo-Fries reaction products on the photodegradation of bisphenol-A polycarbonate. Polym Degrad Stab 2011 96 (12) 2253-2265. 

The photodegradation of unstabilized bisphenol A polycarbonate films is described as an autoaccelerating process initiated by formation of products arising from a formal photo-Fries reaction. Oxidation also contributes as an additional photodegradation pathway. Photosensitive polymers... 

If a polymer contains structures that can absorb terrestrial sunUght wavelengths (>290-300 nm), which leads to chemistry causing changes in molecular structure, photolysis can be an important degradation mechanism. Norrish I and II of carbonyl, ester, or amide containing polymers (e.g., oxidized PE, PES, and PAs) and the photo-Fries reaction in bi-sphenol A polycarbonate (BPA-PC) are well-known photolytic reactions [52]. These reactions are shown in Schemes 18.4-18.6. 

This reaction is important in polymer photochemistry, because it can occur with significant efficiency even in glassy, solid polymers. It is believed to contribute significantly to photo-induced yellowing in aromatic polymers, particularly polycarbonates (Kobsa, 1964 Li and Guillet, 1977). The photo-Fries rearrangement has also been identified as a source of photo-yellowing in aromatic polyamides (Wiles and Carlsson, 1980). 

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