Long-wavelength-absorbing dialkylphenacylsulfonium salt photoinitiators: Synthesis and photoinduced cationic polymerization

A series of sulfonium salt photoinitiators with the general structure Ar′S+CH3(C12H25)SbF, where Ar′ is phenacyl (I), 2-indanonyl (II), 4-methoxyphenacyl (III), 2-naphthoylmethyl (IV), 1-anthroylmethyl (V), or 1-pyrenoylmethyl (VI), were prepared with a novel, simple one-pot process that involves the reaction of an α-bromoalkylarylketone (Ar′Br) with the dialkylsulfide (CH3SC12H25) in the presence of sodium hexafluroantimonate in 2-butanone at room temperature. The photoreactivity of photoinitiators II–VI were evaluated and compared to the unsubstituted analogue, I, in the polymerization of a variety of epoxide monomers. Real-time infrared spectroscopy and differential scanning photocalorimetry studies revealed that the indanonyl initiator II is more active than I. However, sulfonium salts IV–VI, which contain polycyclic aromatic structures, are much less effective as cationic photoinitiators. Interestingly, photoinitiator III is either more or less reactive compared to I, depending on the monomer used. Our work also showed that the efficiency of the unsubstituted phenacylsulfonium salt I can be significantly enhanced through the use of photosensitizers. Mechanistic aspects of the photopolymerization studies are discussed.