Polymethylmethacrylate photodegradation

A polymethylmethacrylate film is transparent and does not absorb solar radiation. Therefore photodegradation of this polymer is relatively small. ESR studies on photo-induced radical formation have been reported by a few workers (90-94). 

Although polymethylmethacrylate is remarkably stable to sunlight, the vacuum photodegradation of this polymer has received considerable attention. Films of polymethylmethacrylate exposed to ultraviolet radiation of 253.7 nm undergo a rapid decrease in molecular weight. The quantum yield of the main chain scission process has been estimated by several authors. Various values have been proposed 1.2 x 10 2 [Ref. 69],... 

Quantum yields of formation have been measured for formaldehyde (2 x 10-2), methanol (1.9 x 10-3) and methyl formate (8 x 10-3) [82]. A modification of the absorption spectrum of polymethylacrylate during irradiation has also been observed (Fig. 14). [82]. The change is similar to that observed with polymethylmethacrylate in the same experimental conditions (Fig. 13) and is probably to be ascribed to the same origin. The photodegradation of polymethylacrylate can be visualized as... 

The mechanism of photodegradation of certain hydroxyphenyl benzotriazole based ultraviolet absorbers has been investigated and a new polymerizable ultraviolet absorber in this group has been synthesized. The photoreactivity is entirely confined at the surface of polymethylmethacrylate films containing the ultraviolet absorbers as pendant groups. A mechanism involving sensitized photooxidation has been proposed to interpret the data. 

Torikai A, Hasegawa A. Wavelength effect on the accelerated photodegradation of polymethylmethacrylate. Polym Degrad Stab 1998 61 (2) 361-364. 

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