Photo degradation

Ranby, B. and Rabek, J., Photo Degradation, Photo Oxidation and Photo Stabilization of Polymers, Wiley, New York, 1975, 75. 

The trend towards miniaturization in microstructure fabrication has created a demand for improved methods of production. The preceding paper (l) detailed one of the areas of research in this area, development of a deep UV-degradable photo-resist and presented a likely candidate, poly(methyl methacrylate-co-3-oximino-2-butanone methacrylate-co-methacrylonitrile) (P(M-OM-CN)). 

Polymer Thermal degradation Photo-oxidation Ozone... 

How does commercial polypropylene degrade photo-oxidatively ... 

D.S. Muggli,A.K. Burkoth,S.A.Keyser,H.R.Lee, mdK.S.Anseth,Reactionbehaviorofbio-degradable, photo-cross-linkable polyanhydrides. Macromolecules 31,4120-4125 (1998). 

Products of degradation - photo-Fries rearrangement producing UV absorber which protects against further degradation ... 

Products of degradation photo-Fries rearrangement chain scissions, crosslinks, free radicals, hydroxyl groups, ethers, unsaturations (photolysis) chain scissions, hydroperoxides, free radicals, hydroxyl groups, carbonyl groups (photooxidation) ... 

Products of degradation photo-Fries rearrangement, yellowing, chains scission, hydroperoxides, carbonyls ... 

Degradation processes during weathering involve photo-radiation, thermal degradation, photo-oxidation and hydrolysis. These irreversible processes can cause... 

Chemical degradation (141), whether thermally or photo-iaduced, primarily results from depolymerization, oxidations, and hydrolysis. These reactions are especially harmful ia objects made from materials that coataia ceUulose, such as wood, cottoa, and paper. The chemistry of these degradation processes is quite complex, and an important role can be played by the reaction products, such as the acidic oxidation products which can catalyze hydrolysis. 

A second degradation process is oxidation, often photo-induced especially by exposure to light not filtered for uv. The radicals resulting from this reaction promote depolymerization of the cellulose, as well as yellowing and fa ding of paper and media. Aging causes paper to become more crystalline and fragile, and this can be exacerbated particularly if the paper is subjected to poor conditions. 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

Water-soluble sdanols such as (1) were found to undergo successive oxidative demethylations with tropospheric ultraviolet irradiation in the presence of suitable chromophores, such as nitrogen oxides (516). The water-soluble methylated sdicones did not promote diatom (Nap cu/apelliculosd) growth but the demethylated photo products did. The sequence of sod-induced degradation of sdicones to water-soluble species such as (1), followed by light-induced conversion to sdicate, suggests a pathway, conceptually at least, for the mineralization of sdicones. 

For more than 20 years, polymer scientists and plastics technologists have been working to develop plastics materials that would be more acceptable environmentally, and in the third edition of this book, published in 1975, the author devoted a section to photo- and biodegradation of polymers. In spite of such effort, an article in 1992 stated that Degradable plastics are still in the early... 

Acrylate polymers also have fully saturated polymer backbones free of any heteroatoms in the main chain. This makes the polymers highly resistant to oxidation, photo-degradation and chemical attack. The acrylate groups are esters, which could be hydrolyzed under severe conditions. However, the hydrophobic nature of most acrylic polymers minimizes the risk for hydrolysis and, even if this reaction happened to some extent, the polymer backbone would still be intact. Other desirable acrylate properties include the following ... 

Kolawole and Olugbemi [156] have published a study of photo and thermal degradation of the two-phase... 

Protection of polymers against thermal and photo-oxidative degradation is achieved with appropriate stabilizers that ensure the desirable polymer properties throughout the entire service life of the polymer. Compatible and polymeric stabilizers usually give the best protection. In order to avoid migration and evaporation, polymeric stabilizers are used. 

Complexed arenediazonium salts are stabilized against photochemical degradation (Bartsch et al., 1977). This effect was studied in the former German Democratic Republic in the context of research and development work on diazo copying processes (Israel, 1982 Becker et al., 1984) as well as in China (Liu et al., 1989). The comparison of diazonium ion complexation by 18-crown-6 and dibenzo-18-crown-6 is most interesting. Becker at al. (1984) found mainly the products of heterolytic dediazoniation when 18-crown-6 was present in photolyses with a medium pressure mercury lamp, but products of homolysis appeared in the presence of dibenzo-18-crown-6. The dibenzo host complex exhibited a charge-transfer absorption on the bathochromic slope of the diazonio band. Results on the photo-CIDNP effect in the 15N NMR spectra of isotopically labeled diazonium salts complexed by dibenzo-18-crown-6 indicate that the primary step is a single electron transfer. 

---