Imaging systems free-radical

Polyhaloalkane-arylamine systems. Free-radical imaging systems utilizing intermediates generated from polyhaloalkane compounds by near-UV radiation and able to react with arylamlnes can form print-out colored images (141). 

More detailed information on free radical systems appears in a general work describing imaging systems (B-76MH1401). 

Photopolymerization is traditionally initiated by direct photolysis of a precursor to provide free radicals via bond homolysis. Examples of such initiators include benzoin, and benzoin ethers, disulfides, and azoalkanes or dialkylperoxides. Hydrogen abstraction chemistry, typified by benzophenone photochemistry, is also recognized as extremely useful. However, a number of viable commercial photopolymer imaging systems are based upon ionic (especially cationic) polymerization. These systems will be discussed next. 

Simultaneous Radical and Acid Catalyzed Condensation Polymerization. As shown in Equations 1-7, the photolysis of diaryliodonium and triarylsulfonium salts produces in addition to strong protonic acids, a variety of radical fragments. These photoinitiators are, therefore, capable of initiating free radical polymerizations. A number of hybrid imaging systems which take advantage of both radical and acidic species formed from the photolysis of these salts have been designed. For example, Equation 26 illustrates one such system based on simultaneous radical and acid catalyzed condensation polymerizations which has been explored in our laboratory. 

The requirement of the presence of the polymerization catalyst in the depolymerization process stems from the principle of microscopic reversibility. If, for example, all free radicals are removed from the system by simply endcapping the polymer, the thermodynamic equilibrium dictates that depolymerization state cannot be reached and the system will be stable. This was the approach employed by Ito and Willson in stabilizing polyphthaldehyde resists. [See for example, C.G. Willson, H. Ito, J.M.J. Frechet, T.G. Tessier, F.M. Houlihan, Approaches toward the design of radiation sensitive polymeric imaging systems with improved sensitivity and resolution, J. Electro chem. Soc. 133, 181 (1986)]. 

A possible autocatalytic reaction will be discussed later with a free-radical Imaging system. 

IX. FREE-RADICAL IMAGING SYSTEMS A. Triarylitnidazolyl Systems... 

Paczkowski J, Neckers DC (2001) Photoinduced electron transfer initiating systems for free-radical polymerisation. In Balzani (ed) Electron transfer in chemistry molecular level electronics, imaging, energy and environment, vol V. Wiley-VCH, Weinheim, pp 516-585... 

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