Visible Light-Induced Cationic Polymerization Using Fullerenes

A novel visible light sensitive photoinitiator system for the cationic polymerization of typical monomers, for example, of oxiranes, such as cyclohexene oxide, vinyl ethers, such as iso-butyl vinyl ether, and other vinyl monomers, such as N-vinylcarbazole, using fullerene derivatives is described. The cationic polymerization of these monomers was initiated at room temperature upon irradiation in the visible region (lambda(inc) > 400 nm) in bulk or chlorobenzene solutions with polystyrene-C-60 (PS-C-60) adduct or bare C-60, respectively, in the presence of oxidizing salts such as silver hexafluorophosphate (AgPF6) and diphenyliodonium hexafluorophosphate (Ph2I+PF6-). A feasible mechanism, as correlated with optical absorption measurements, free energy changes (Delta G), and proton scavenging studies, involves formation of exciplex by the absorption of light in the first step. Subsequent electron transfer from excited C-60 or PS-C-60 to oxidizing salt yields radical cations of the fullerene derivatives. Both radical cations and a strong Bronsted acid derived by hydrogen abstraction initiate the cationic polymerization of a variety of monomers.