Polymer photosensitized degradation

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. 

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. 

Sakai, W., Kinoshita, M., Nagata, M. and Tsutsumi, N. (2001) ESR studies of photosensitized degradation of poly(L-lactic add) via photoionization of dopant. Journal of Polymer Science Part A Polymer Chemistry, 39,706-714. 

Polyolefins such as PE and polypropylene (PP) are usually not accessible to direct microbial attack. For such polymers, biological degradability is achieved hy the addition of starch, prooxidant additives or photosensitive components. Starch, a natural polymer, can he degraded by microorganisms which enhances the defragmentation of the polyolefins (if the starch is accessible to the microbes). The additives increase the initial reduction of polymer chain length by chemical... 

Dye photosensitized degradation of polymers is a phenomenon commonly known in industry as phototendering. However, the mechanism of phototendering not only involves the singlet oxygen oxidative mechanism, but also various free radical processes, the formation of oxygen radical ions ( 2 ) and other oxygen reactive species, and it is very complex. 

Support for the conjugated alkene photosensitized degradation of poly(vinyl chloride) comes from the observation that photolysis of thermally degraded polymer (which contains conjugated polyene sequences) gives a substantially increased rate of dehydrochlorination [11]. 

Most synthetic and natural polymers degrade when exposed to solar ultraviolet (UV) radiation (1-5). In synthetic polymers degradation is generally caused by the presence of photosensitive impurities and/or abnormal structural moieties which are introduced during polymerization or in the fashioning of the finished products. The presence of groups such as ketones, aldehydes, peroxides and hydroperoxides are implicated in polymer degradation (1-5). 

---