The discovery and development of onium salt cationic photoinitiators

The story of the discovery and development of onium salt photoinitiators fo r cationic polymerization is chronicled. The chemistry of the synthesis of these compounds is outlined, and the mechanisms of their initiation are dis cussed briefly. Among the most useful of these types of photoinitiators are diaryliodonium and triarylsulfonium salts, which are used widely for photo induced cationic crosslinking reactions. From the very beginning, onium sal t photoinitiated cationic polymerizations have found use in a multitude of practical applications. Specifically discussed in this article are the use of onium salts in coatings, adhesives, printing inks, release coatings, ste reolithography, holographic recording, photocurable composites, and microel ectronic photoresists. (C) 1999 John Wiley & Sons, Inc.