Anthracene-bound sulfonium salts: highly efficient photoinitiators for cationic polymerization: A new synthesis of sulfonium salts which avoids the use of silver salts

The low absorptivity of triarylsulfonium salts above 320 nm limits their utilization of longer wavelength emission from light sources. Herein we report the synthesis and photoactivity of anthracene-bound sulfonium salts, in which the sulfonium salt is insulated from the anthracene chromophore by a saturated chain. The salts efficiently absorb radiation between 330 and 410 nm owing to the strong anthracene absorptivity in this spectral region. The efficiency of utilization of the absorbed radiation for generating cationic initiators is strongly dependent on the substituents attached to the sulfonium ion. Evidence is presented in support of generation of initiators for cationic polymerization by photo-induced electron transfer from the anthracene chromophore to the sulfonium group, wherein the efficiency of electron transfer is dependent on the sulfonium ion substituents. A new synthesis of sulfonium salts is also provided, which occurs by direct alkylation of diaryl dialkyl and arylalkyl sulfides by oxiranes in the presence of strong acids having non-nucleophilic anions.