Styrene oxide, photopolymerization

Figure 4. Photopolymerization of styrene oxide using 10% (C6H5)sS" X salts...

A detailed study of mechanisms both of photodecomposition of triarylsul-fonium salts to yield Bronsted acids and of catalysis of cationic polymerization of representative monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran (THF), and 2-chloroethyl vinyl ether—was reported in 1979 by Crivello and Lam [14]. Crivello [15] and Green et al. [16] provided further reviews shortly thereafter. The mechanisms of photodecomposition of a variety of initiators for free radical photopolymerization, including onium salts, were compared by Vesley [17] in 1986. A review, similar in scope, but providing more mechanistic detail was also published in 1986 by Timpe [10a]. An updated coverage of aspects of this chemistry has been provided by the same author in his review of photoinduced electron transfer polymerization [10b]. 

A wide assortment of additional electron-transfer PSs for diaryliodonium salts have been described in the journal and patent literature. These include ketocoumarins [FOU 88], 9,10-phenanthraquinone [BAU 86], Mannich bases [DE 88b], 1,3-indanediones [TEH 13], benzoquinonylsulfanyl derivatives [SUG 03], acridinediones [SEE 01] and dimethylaminobenzylidine derivatives [ICH 87], In addition, the use of dyes such as eosine and Rhodamine [DE 88a, DE 89] have been employed to provide photosensitization in the visible region of the spectrum. A particularly interesting system devised by Yagci et al. [AYD 08] is the dithienothiophene, 48, used with diphenyliodonium hexaflurophosphate to carry out the cationic photopolymerizations of cyclohexene oxide, 3,4-epoxycyclohexylmethyl 3, 4 -epoxycyclohexane carboxylate, N-vinyl carbazole, n-butyl vinyl ether and styrene. These investigators have further applied this system to the preparation of metallic silver-filled epoxy nanocomposites [YAG 11]. 

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