Polymethylmethacrylate Photolysis

Kato et al. (92) irradiated polymethylmethacrylate at -196° C under vacuum, and the spectrum shown in Fig. 16 was obtained. This spectrum was identified as due to the free radicals, COOCH3, CHO, and -CH3, which show the singlet, doublet and quartet, respectively. The half-life of methyl radicals at — 196° C was about 5 hr. It is likely that the methyl radicals are produced by the photolysis of ester side groups, just as ethyl radicals are produced after irradiation of polyethyl-methacrylate at —196° C. 

Volatile product evolution has been observed in the photolysis of many vinyl polymers as a consequence of side-group scission. The nature of these volatile products is therefore related to the side group. Carbon dioxide, carbon monoxide and methyl formate are produced from polymethylmethacrylate [12], carbon dioxide, carbon monoxide, methane and acetic acid in the photolysis of poly vinylacetate [13], and hydrogen chloride in the photolysis of polyvinylchloride [14]. 

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... 

One important exception to this rule is vinylketone polymers in which the Norrish type II reaction is responsible for the decrease of the molecular weight of irradiated polymers (see section 4). In contrast to polymethylmethacrylate, polymethylacrylate becomes insoluble on irradiation with 253.7 nm in vacuo [82]. In air, no visible insoluble material is formed and an apparent quantum yield of chain scission of 1.3 x 10-2 has been determined by viscosity measurements [82]. However, a qualitative comparison of sedimentation patterns of initial and irradiated samples indicates that crosslinking also occurs in the presence of air even if gelation is retarded by oxygen. This makes the above-mentioned value meaningless. Photolysis of thin polymethylacrylate films at 253.7 nm in vacuo has also been studied by measuring the insoluble fraction as a function of dose as described in section 2. Quantum yields of 1.9 x 10-3 have been estimated for both the chain scission and the crosslinking processes [83]. 

As the gaseous products formed in the photolysis of polymethylacrylate and polymethylmethacrylate are identical, it seems clear that the... 

During the photolysis of polymethylmethacrylate (PMMA) in an atmosphere of NO by unfiltered light of a mercury lamp at room temperature, the formation of acylalkylaminoxyl radicals such as Rj-N0 -C(=0)-0R2 was observed with... 

Observation of redox pairs on longer timescales characteristic of nanosecond laser-flash [188] or conventional flash spectroscopy [189,190] provides further support for the (direct) electron transfer via CT irradiation. Thus ferricenium cation is observed at comparatively early (20 )is) times upon (conventional) flash photolysis of the [Cp2Pe, CBr4] complex in both acetone solvent and polymethylmethacrylate films [191]... 

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