Degradation photosensitized

Ranby and Rabek have reviewed in depth the mechanisms by which various species sensitize the photodegradation of polymers. 

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Unimolecular and Bimolecular Rate Constants for the Different Elementary Steps Involved in the MB Photosensitized Degradation of Bixin in Acetonitrile Methanol (1 1) Solutions at 25°C... 

Literature references on the ozonation of A07 indicate that the molecule in such an oxidative degradation is cleaved at the point where the azo bond is attached to the naphthalene moiety giving rise to the intermediate, 1,2 naphthoquinone (NQ) [260,261]. This intermediate is oxidized subsequently to a phthalic acid derivative. The spectrum of the photolyzed A07 was found to be similar, especially in the area of 1400 to 1800 cm-1, to the spectra of the photolyzed naphthoquinone samples. It is reasonable to conclude therefore that naphthoquinone is an intermediate from the photosensitized degradation of A07 on Ti02. The naphthoquinone then undergoes further degradation to form a phthalic acid derivative. The end product of oxidation of A07 is an aromatic carboxylic acid as characterized from the peak at 1700 cm-1. 

Tada, M., Kobayashi, N., Kobayashi, S. 1971. Studies on the photosensitized degradation of food constituents. II. Photosensitized degradation of methionine by riboflavin. J. Agric. Chem. Soc. Japan 45, 471—476. 

Cimningham JA-SG, Sedlak P, Caffrey J. Aerobic and anaerobic TiO -photocatalysed purifications of waters containing organic pollutants. Catal Today 1999 53 145-158. Penuela GAB, Damia. Photosensitized degradation of organic pollutants in water processes and analytical applications. Trends Anal Chem 1998 17 605-612. 

This Report follows the format of the previous one except that, commencing this year, the patents section will be omitted. Academic and industrial research in this field continues to be prolific, particularly in areas of photopolymerization such as electron beam curing and photoresists. Other areas, such as the photosensitized degradation of polymers for producing photodegradable plastics, have diminished to only a few articles, and consequently these will now be included in the section dealing with photo-oxidation and photodegradation. 

In photosensitized degradation of polymers it is most important to know whether the transferred energy is suffioient to effeot the scission of bonds in aoceptor macromolecules. 

The photosensitizing degradation may considerable contribute to the solution of the plastic-litter problem. In order to improye the standards of our enyironment the amounts of plastic litter should be reduced and this aim may easily be aohiyed by the use of plastics mhich would readily degradable by sunlight. This practioal problem has been fully reviewed by the following publioations (3,127). 

Stannett and coworkers (17, 18) have shown that anthraquinone-sensitized photopolymerizations on celluloses and nylon involve the triplet state of the dye and semiquinone intermediates in photoinitiation. In addition, anthraquinones (17, 18) were also known to photosensitize degradation of polymers. 

Photosensitized degradations of substrates (PC or PMMA) by colourants in optical disc have to be considered, as some dyes and pigments having an absorption band in the visible region have a destabilizing effect on the light stability of polymer (39). However, no systematic investigations of that problem has been published yet, as far as we know. 

Photosensitized degradation of poly(olefin sulfones) similar to the Hg(3P) photosensitized reactions of olefin sulfones make them subject to photodegradation in easily accessible wavelength regions. Almost all poly(olefin sulfones) have been reported only as positive tone electron beam resists (4). As the only exception, poly(5-hexene-2-one sulfone) has been reported as a positive tone photoresist with or without a photosensitizer, benzophenone (5). Because this polymer has a carbonyl chromophore, its photosensitivity is clearly derived from the polymer structure itself. 

Baldursdottir, S.G., Kjpniksen, A.-L., Roots, J., Tpnnesen, H.H., and Nystrpm, B. (2003b) Influence of concentration and molecular weight on the photosensitized degradation of alginate in aqueous solutions, Polym. Bull., 50, 373-380. 

This reaction was reported for the benzophenone photosensitized degradation of polypropylene (92),polystyrene (95), poly(vinyl alcohol) (94),polyisoprene (95,96),polyurethane (97) and polyadenylic acid (98) In solid state benzophenone also produce an extensive crosslinking of polyethylene (99-105) It has also been found that benzophenone and its derivatives caused an initial rapid oxidation,increasing with ketone concentration (70) Currently the relative importance of singlet oxygen formation in energy transfer reaction between excited benzophenone and molecular oxygen is discussed (92,104) ... 

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