Initiators based on photofragmentation

The main classes of initiators based on photofragmentation (scission of covalent bonds) are limited to UV applications, and they include peroxides, azo compounds, benzoin derivatives, acetophenone derivatives, ketoxime esters of benzoin, tri-azines, etc. On photolysis, these classes of initiators, depending on their wavelength of sensitivity, are able to initiate the polymerization of monomers such as methyl methacrylate in negative-tone lithographic imaging. 

Reiser, Photoactive Polymers The Science and Technology of Resists, p. 107, John Wiley Sons, Hoboken, NJ (1989). 

Photoscission is particularly efficient in the alkyl ethers of benzoin, and these are among the most widely used photoinitiators in the UV curing industry. The benzoyl alkyl ethers absorb between 330 and 350 nm. ° Both the benzoyl 

The search for molecules that can absorb at 365 nm (the principal emission of the Hg arc in the UV) and that dissociate on excitation started with acetophenone. 

Pappas and R.A. Asmus, Photoinitiated pol3fmerization of methyl methacrylate with benzoin methyl ether. IE. Independent photogeneration of the ether radical, J. Polym. Set, Polym. Chem. Ed. 20, 2643 (1982). 

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