Photostabilisation

Kim el al. [582] have described maleimide-based antioxidants melt grafted onto low-MW PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Smedberg el al. [583] have characterised polymer-bound stabilisers by FTIR and NMR. The binding of antioxidants and photostabilisers to polyurethanes was verified by tJV/VIS spectroscopy [584]. 

Langer H, Doltsinis NL (2003) Selected photostabilisation of guanine by methylation. Phys Chem Chem Phys 5 4516-4518... 

Only a limited range of nitro, azo and anthraquinone disperse dyes exhibit adequate fastness to dry heat, light and weathering for application on polyester automotive fabrics. The structure of Cl Disperse Yellow 86 was modified to incorporate UV absorbers of the benzophenone, benzotriazole or oxalanilide types into the dye molecule. The derived dyes showed better fastness properties than the parent unsubstituted dye. Positioning of the photostabilising moiety within the dye molecule had little influence on the light fastness obtained, however. Built-in benzophenone residues were more effective than the other two types [177]. Nevertheless, several further monoazo and nitrodiphenylamine disperse dye... 

Consider the photodegradation of polystyrene in sunlight (Scheme 9.5). Polymer photodegradation can be slowed down by adding photostabilisers, which may be ... 

Recently, Loden et al. [83] investigated the use of titanium dioxide as an opaci-fier in topical formulations of ketoprofen. The results demonstrated qualitative differences in the level of photostabilisation based on the grade of titanium dioxide utilised. Surface-coated particles were shown to induce greater photostabilisation than pharmaceutical grades of the excipient. The authors showed clear superiority of the opacified topical formulation containing 4% titanium dioxide versus the standard clear gel. 

Teraoka R, Matsuda Y, Sugimoto I. Quantitative design for photostabilisation of nifedipine by using titanium dioxide and/or tartrazine as colorants in model film coating systems. J Pharm Pharmacol 1989 41 293-297. 

K. Thoma, R. Klimek, Photostabilisation of drugs in dosage forms without protection from packaging materials. Int. J. Pharm. 67 169-175, 1991. 

H. Oda, Photostabilisation of photochromic materials contribution of amphoteric counterions on the photostability of spiropyrans and related compounds, Dyes Pigm., 23, 1-12 (1993). 

Journal of Vinyl and Additive Technology 1, No.4, Dec. 2001, p.235-43 PHOTOSTABILISATION OF POLY(VINYL CHLORIDE) BY PROTECTIVE COATINGS... 

A number of reviews on polymer photostabilisation have appeared " as well as the stabilisation of ceramic paints clearcoats, wood finishes and car body paints . Hindered piperidine stabilisers (HALS) have also been reviewed in depth " and the surface stabilisation of polystyrene covered . ... 

The dielectric strength of polyethylene has been measured as a function of additive concentration while in stabilised polymers the depth of degradation was found to be uniform . HALS have been found to be effective stabilisers for UV cured coatings and do not influence the cure rate . Bleached wood pulps can be effectively stabilised by ascorbic acid and wool by hydroxy-benzotriazoles and HALS . Hydroxybenzotriazole stabilisers also protect wood pulp and polyurethanes by co-reaction . The spectroscopic properties of monomeric and polymeric benzotriazoles have also been compared . UV absorbers are effective in clear coats and when grafted to wood . Dihydroxybenzophenone stabilisers inhibit the chain scission in the photodegradation of poly(methoxyacrylophenone) while tin stabilisers have also been found to photostabilise PVC . 

The photostabilisation of polymers still maintains a high level of activity with the mechanistic action and performance of hindered piperidine compounds continuing to attract interest. Some interesting reviews have appeared with one very extensive and highly recommended paper on the mode of action of hindered piperidine light stabilisers while another has dealt with their manufacturing properties. The kinetic reactions and photophysics of light stabilisers have been covered in another review as has the stabilisation of polyacetals. ... 

Lu et al. have reported that the fluorescence intensities of Eu3+ and Tb3+ are markedly enhanced when they are bound on to a poly(acrylamide-acrylic acid copolymer). Dhake et al. have observed interesting differential effects of pressure on the fluorescence of a polymer and the corresponding monomer. Sterically hindered piperidines have for long been of interest as efficient photostabilisers of polymers. Gugumus has now reported that these stabilisers form charge-transfer complexes with molecular oxygen, thereby preventing the formation of such complexes with the polymer. 

Consequently inter-laboratory comparisons of uv stability of polymers and the effects of uv stabilisers is normally difficult if not impossible. There is evidence that in some cases the role of photostabilisers has been confused with that of thermal stabilisers since the two are mechanistically related (11). Just how important can be the prior thermal history of polyethylene on its uv stability is shown in Figure 1 which relates the processing time under standard conditions to the time to embrittlement in a standard sunlamp / blacklamp (S/B) environmental simulator. Figure 1 also shows the... 

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