Ketone polymers photochemistry

Photochemistry of Ketone Polymers in the Solid Phase A Review... 

Polymer Photochemistry. The occurrence of these reactions in polymeric ketones was first demonstrated by Guillet and Norrish (6, 7), who studied poly (methyl vinyl ketone) in solution and showed that the main features of the photodegradation could be accounted for quantitatively on the basis of Type I and Type II reactions. The conclusion was later confirmed by Wissbrun (13). Recent studies of the ethylene-carbon monoxide polymer (9) confirm that both Type I and Type II reactions occur. The Type I reaction results in the formation of two polymer radicals, one of which is an acyl radical which may subsequently decarbonyl-ate (Reaction 4). 

Somersall, A. C., Guillet, J. E., Photochemistry of Ketone Polymers VIII, ... 

Much work has been devoted to the photochemistry of ketone polymers despite their limited commercial application. The main reason for this is that initiation of the photodegradation of different polymers is attributed to carbonyl groups incorporated during manufacture or processing. Another reason is that the photochemistry of low molecular weight ketones is the most thoroughly studied of any class of compounds and is now comparatively well understood, so the mechanism of the photodegradation of ketone polymers can be established on a sounder base. 

Amerik and J.E. Guillet, The Photochemistry of ketone polymers. IV. Photolpsis of methyl vinyl ketone copol3miers, Macromolecules 4, 375 (1971) E. Dan and J.E. Guillet, Photochemistry of ketone polymers. X. Chain scission reaction in the solid state, Macromolecules 6, 230 (1973). 

Figure 5. Quantum yield for carbon monoxide evolution (< >co) function of chain length temperature, 120°C solvent, paraffin oil. Reprinted with permission from G. H. Hartley and J. E. Guillet, Photochemistry of Ketone Polymers II. Studies of Model Compounds, Macromolecules, 1, 415 (1968).

Further confirmation of the important effect of solid-phase transitions in polymer photochemistry was reported by Dan and Guillet (29). They studied the quantum yields of chain scission, c >s, as a function of temperature in thin solid films of vinyl ketone homo- and copolymers. For polymers where the Norrish type-II mechanism was possibici large increases in n were observed at and above the glass transition T. Figure 8 shows this effect in a styrene copolymer containing about 5% phenyl vinyl ketone (PVK). Below Tg, )s is about 0.07, but at Tg it rises to about 0.3, a value similar to that observed for photolysis in solution at 2S°C. A similar effect was observed with poly (methyl methacrylate-co-methylvinyl ketone) (PMMA-MVK) and PVK homopolymer. 

Hartley, G. H. and Guillet, J. E. (1968) Photochemistry of ketone polymers. I. Studies of ethylene-carbon monoxide copolymers. Micromolecules, 1, No. 2 March-April, 165-9. 

Hartley, G.H., Guillet, J.E. Photochemistry of ketone polymers. I. Smdies of ethylene-carbon monoxide copol5nners. Macromolecules 1(2), 165-170 (1968)... 

Golemba, F.J., and J.E. Guillet (1972), Photochemistry of ketone polymers. V. Photochemistry of the linear 2-aUcanones in solution. Macromolecules, 5, 63-68. 

This paper reports a study of the photochemistry of polymers and copolymers containing o-tolyl vinyl ketone units. 

The ketone group is a useful model for other types of chromophores because it can be selectively excited in the presence of other groups in polymer chains such as the phenyl rings in polystyrene and so the locus of excitation is well defined. Furthermore there is a great deal known about the photochemistry of aromatic and aliphatic ketones and one can draw on this information in interpreting the results. A further advantage of the ketone chromophore is that it exhibits at least three photochemical processes from the same excited state and thus one has a probe of the effects of the polymer matrix on these different processes by determination of the quantum yields for the following photophysical or photochemical steps l) fluorescence,... 

The study of the photochemistry of inorganic and organic compounds gives valuable information on their photolysis during which free radicals are formed (10-12). Extensive studies have especially been made in the field of photochemistry of aliphatic ketones,ethers and peroxides (12-14) All these compounds have been found to be good photoinitiators which initiate degradation and crosslinking of polymers. The mechanism of these reactions seems to be simples... 

Koch and A.H. Jones, A photochemical exchange reaction of Michler s ketone, J. Am. Chem. Soc. 92, 7503 (1970) D.I. Schuster and M.D. Goldstein, Photochemistry of ketones in sol ution. XXXVII. Plash photolysis of Michler s ketone in solution. Rate constants for decay and triplet excimer formation, J. Am. Chem. Soc. 95, 986 (1973) V.D. McGinnis and D.M. Dusek, Photopolymerization of methyl methacrylate with the use of 4,4 BIS (diethylamion) benzophenone as the photoinitiator, ACS Polym. Prepr. 15(1), 480 (1974). 

The largest body of experimental work on the photochemistry of solid polymers relates to the study of the photolysis of homo- and copolymers of vinyl ketones. In early work, Guillet and Norrish (20) and Wissbrun (21) showed that polymeric ketones such as poly(methylvinyl ketone) and poly(methylisopropenyl ketone) underwent the same classical photochemical reactions as their low-molecular-weight analogs. The photophysical and photochemical processes which occur are summarized below ... 

Figure 7. Relative rates for carbonyl loss (type I) in films of ethylene-ketone copolymers under nitrogen at constant light intensity (26). Reprinted with permission from F. Sitek, J. E. Guillet, and M. Heskins, Some aspects of the photol)rsis and photochemistry of PE coatmaingV aasgioaps, Journal of Polymer Science-Polymer Symposia, 57,351 (1976). Copyright 1976, John Wiley Sons, Inc.

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