Thermally Initiated cationic arylation

The initial development of diaryliodonium salt cationic photoinitiators was quickly followed by the nearly parallel discovery of triarylsulfonium salts as a second general class of highly efficient and thermally stable cationic photoinitiators. Along with triarylsulfonium salts, 77, their S-aryl sulfiir-heterocyclic analogs display good photosensitivity and function well in photoinitiated cationic polymerizations. 

Two other patents have also appeared describing the use of alternate free radical sources as reducing agents for diaryliodonium and triarylsulfonium salts Crivello and his coworkers have discovered several other types of reactions which can be used to thermally induce cationic polymerization using onium salt photoinitiators. Diaryliodonium salts are thermally decomposed in the presence of catalytic amounts of copper compounds An organocopper compound is proposed as an intermediate which undergoes electrophilic arylation of cationally polymerizable monomers as shown in Scheme 14 to initiate polymerization. 

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