Photochemical degradation polymers

Functional dyes (1) of many types are important photochemical sensitizers for oxidation, polymerization, (polymer) degradation, isomerization, and photodynamic therapy. Often, dye stmctures from several classes of materials can fulfiH a similar technological need, and reviewing several dye stmctures... 

Aqueous plutonium photochemistry is briefly reviewed. Photochemical reactions of plutonium in several acid media have been indicated, and detailed information for such reactions has been reported for perchlorate systems. Photochemical reductions of Pu(VI) to Pu(V) and Pu(IV) to Pu(III) are discussed and are compared to the U(VI)/(V) and Ce(IV)/(III) systems respectively. The reversible photoshift in the Pu(IV) disproportionation reaction is highlighted, and the unique features of this reaction are stressed. The results for photoenhancement of Pu(IV) polymer degradation are presented and an explanation of the post-irradiation effect is offered. 

Functional dyes of many types are important photochemical sensitizers for chemical reactions involving oxidation, polymerization, (polymer) degradation. isomerization, and photodynamic therapy. Often, dye structures from several classes or materials can fulfill a similar technological need, particularly for laboratory or small-scale reactions where production efficiency may be of secondary importance. Commercial photochemical technology, however, is more selective and requires photochemical efficiency, ease of product separation, and lack of unwanted side reactions to an extent similar to that required by imaging processes. In addition, reusability of the spectral sensitizer is also preferred in commercial photochemical reactions. 

The ability of two geminate radicals to escape from each other and thereby avoid radical-radical recombination is a key mechanistic feature that determines the rate of polymer degradation (Scheme 10). As shown in the discussion, the existence of a photochemically generated radical pair containing... 

Photochemical degradation of Iignocellulosic Materials Hon, D. N.-S. Grassie, N. Ed. Developments in Polymer Degradation Applied Science Publishers London, U.K., 1991. 

D.N.-S. Hon, Photochemical Degradation of Liqnocellulosic Materials in Developments in Polymer Degradation - 3... 

Alternative Polymer Degradation Processes, (e.g., Photochemical, Plasma,... 

Pospfsil J (1993) Chemical and photochemical behavior of phenolic antioxidants, a state of the art report, part I, Polym Degrad Stab 40 217-232. 

Hon DNS (1982) Photochemical degradation of lignocellulosic materials In Grassie N (ed) Development in polymer degradation 3 Applied Science Publishers, Essex, England, 229-281... 

A detailed description of bulk polymers as hosts for geminal radical pairs and their precursors is also beyond the scope of this chapter. For general sources of information about photochemical and photophysical processes in bulk polymers, we recommend the classic book by Guillet as well as the book edited by Winnik, the journal Polymer Degradation and Stability (incorporating the defunct journal. 

Structure and mechanism in photochemical reactions. The reactions of geminal radical pairs created in bulk polymers are presented by Chesta and Weiss in Chapter 13. Of the many possible chemical reactions for such pairs, they are organized here by polymer and reaction type, and the authors provide solid rationalizations for the observed product yields in terms of cage versus escape processes. Chapter 14 contains a summary of the editor s own work on acrylic polymer degradation in solution. Forbes and Lebedeva show TREPR spectra and simulations for many main-chain acrylic polymer radicals that cannot be observed by steady-state EPR methods. A discussion of conformational dynamics and solvent effects is also included. 

Singlet oxygen is involved in many important chemical processes and photochemical applications, including photodynamic therapy (Special Topic 6.23), photocarcinogeneity (Special Topic 6.7) and phototoxicity (Special Topic 6.22), chemiluminescence (Section 5.6), atmospheric photochemistry (Special Topic 6.21), polymer degradation (Special Topic 6.13), photosynthesis1389 (Special Topic 6.25) or industrial organic synthesis (Special Topic 6.20). 

J. Pospisil, Chemical and photochemical behaviour of phenolic antioxidants in polymer stabilization a state of the art report, Part II, Polym. Degrad. Stab. 1993, 39, 103-115. 

N.S. Allen, A. Parkinson, F.F. Loffelman, and P.V. Susi, Photo-Stabilising action of ap-hydroxybenzoate compound in polyolefins. Part I. Thermal and photochemical behaviour in polypropylene film, Polym. Degrad. Stab. 1983, 5, 241-266. 

The major causes of instability of cellulose nitrate are due to the products of hydrolytic, thermal and photochemical reactions. Degradation of the polymer is autocatalytic, that is, the products of breakdown tend to catalyse a faster and more extensive degradation reaction than the primary processes, if allowed to remain in contact with degraded cellulose nitrate. 

RIV 02] Rivaton a., Mailhot B., Soulestin I, et al., Comparison of the photochemical and thermal degradation of bisphenol-A polycarbonate and tiimethylcyclohexane-poly-caihormte . Polymer Degradation and Stability, vol. 75, no. l,pp. 17-33,2002. 

A. Rivaton, B. Mailhot, S. Robu, M. Lounad, P. Bussiere, and J.-L. Gardette. Photophysical processes and photochemical reactions involved in poly(M-vinylcarbazole) and in copolymers with carbazole units. Polym. Degrad. Stabil, 91(3) 565-572, March 2006. 

El Aidani R, Nguyen-Tri P, Malajati Y, Lara J, Vu-Khanh T. Photochemical aging of an e-PTEE/Nomex membrane used in firefighter protective clothing. Polymer Degrad Stabil 2013 98(7) 1300-10. 

Hindered amine light stabilizers (H ALSs) have been described in detail (25). They are derivatives of 2,2,6,6-tetramethyl piperidine and are extremely efficient stabilizers against the light-induced degradation of polymers. HALS do not absorb any UV radiation, but they inhibit the degradation of a pol5mer. In particular, they slow down the photochemically initiated degradation reactions in a similar way as antioxidants (26). 

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