Photochemistry of methacrylate and acrylate polymers

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], 

Volatile products are evolved during the photolysis of polymethylmethacrylate. By far the greatest proportion of low molecular weight fragments consists of carbon monoxide, methyl formate and methanol [12, 72]. The last two products are formed with quantum yields of 0.14 and 0.48, respectively [12]. Methane, hydrogen and carbon dioxide are also produced [12]. Except for hydrogen, all the volatiles have been 

Since the ester side group is the chromophore in polymethylmethacrylate, the initial step in the photolysis is likely to be 

However, since the yield of methanol is four times higher than that of carbon monoxide [72], another reaction has to be taken into account namely, 

293 nm and the absorption coefficient is 11.8 1 mole-1 cm-1 at that wavelength. It has also been suggested that the change in the absorption spectrum could be attributable to the formation of conjugated double bonds [72] according to 

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