Cationic photopolymerization method

Diaryliodonium salts are widely used as photoinitiators for cationic photopolymerizations [17-20]. Photoini-tiated cationic polymerization is of great practical interest due to its applicability for the curing of coatings and printing inks and for photoresist technology used in lithography [19,20]. General synthetic methods, properties and photochemistry of diaryliodonium salts as photoinitiators were reviewed by Crivello in 1984 [18]. 

Minns, R.A., and Sdiild, H.G. (1996) Cationic ring-opening photopolymerization methods for volmne hologram recording. Proc. SPIE, 2689,127 (b) (1998) Holographic Medimn and Process for Use Thereof. US Patent 5,759,721. 

Many different methods have been used to monitor the kinetics of cationic ring-opening photopolymerizations. Among the most commonly used techniques are real-time infrared spearoscopy, differential scanning photocalori-metry, " thin-film calorimetry, and optical pyrometry. ... 

Obviously, one could also use the benzoin site of the azo-benzoin initiator for a photopolymerization in the first step and activate the azo sites in a subsequent, thermal reaction [213]. However, regarding homopolymer formation, the method depicted in reaction (47) has to be given priority because benzoin groups are thermally stable, whereas azo groups may be photolyt-ically ruptured. Benzoin-azo initiators are, furthermore, suitable for the synthesis of block copolymers with one of two monomers being cationically polymerizable [214,215]. 

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