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Photoinitiated cationic polymerization by photosensitization of diphenyliodonium and triphenylsulfonium salts is shown to proceed by two distinct electron transfer process: (1) direct electron transfer from excited‐state photosensitizers and (2) indirect electron transfer from photogenerated radicals. The efficiency of the former process is attributed to the instability of the reduction products (from diphenyliodonium and triphenylsulfonium salts), which dissociate in competition with undergoing energy‐wastage reverse electron transfer. Amplification of photons in the production of protons (or other reactive cations) is postulated to account for the high quantum yields observed in the latter process. Potential advantages of utilizing the indirect redox process in the design of UV curable hybrid systems, which contain functionality for both radical and cationic polymerization, are noted. The results also provide evidence against the importance of triplet states of the onium salts in photoinitiator activity.

Laser flash photolysis of diphenyliodonium salts produces phenyliodinium radical cation (PhI+·), which was also generated independently by flash‐induced electron transfer from iodobenzene to a phenanthrolinium salt. Apparent second‐order rate constants were determined for reaction of the transient (PhI+·) with nucleophiles, including iodobenzene and cyclohexene oxide. Quantum yields of formation of acid from stationary photolysis of diphenyliodonium hexafluoroarsenate were found to be significantly higher than yields of iodobenzene. These results may be explained by facile reaction of PhI+· with PhI to yield a new iodonium salt together with a proton. High reactivity of PhI+· with cyclohexene oxide suggests that the transient may directly initiate cationic polymerization of epoxides.

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SynopsisUnambiguous I3C-NMR assignments for the primary (prim-) and secondary (sec-) isocyanate carbons of isophorone diisocyanate (IPDI) have been made by using two-dimensional NMR measurements. On the basis of the assignments, relative reactivity of the prim-and sec-isocyanate groups with n-butanol was studied by quantitative I3C-NMR analysis. The individual stereoisomers of IPDI (Z-IPDI and E-IPDI) and their equimolar mixture were reacted with n-butanol (IPDI/ n-butanol = 2/1 molar ratio) at 5OoC for 3 days. It was found that the sec-NCO is about 1.6 times more reactive than the prim-NCO in both Z-and E-isomers. Reactivity of the E-isomer was found to be slightly higher than that of the Z-isomer. When di-n-butyltin dilaurate (DBTDL) was used as a catalyst, the reactivity of the sec-NCO became about 12 times higher than that of the prim-NCO with both isomers. In the case of 1,4-diazabicyclo[ 2.2.21 octane (DABCO) catalyst, theprim-NCO was 1.2 times more reactive than the sec-NCO with both isomers. Fig. 3. Urethane carbon region of %NMR spectra: ( a ) Reaction 1 (Z-isomer), (b) Reaction 2 (E-isomer), ( c ) Reaction 3 ( Z -/ E -= 1/1, no catalyst), ( d ) Reaction 4 (Z-/E-= 1/1, DABCO catalyst), ( e ) Reaction 5 ( Z -/ E -= 1/1, DBTDL catalyst).