Visible Light-Induced
Cationic Polymerization Using
Fullerenes
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Abstract
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 <i>N</i>-vinylcarbazole,
using fullerene derivatives is described. The cationic polymerization
of these monomers was initiated at room temperature upon irradiation
in the visible region (λ<sub>inc</sub> > 400 nm) in bulk
or
chlorobenzene solutions with polystyrene-C<sub>60</sub> (PS-C<sub>60</sub>) adduct or bare C<sub>60</sub>, respectively, in the presence
of oxidizing salts such as silver hexafluorophosphate (AgPF<sub>6</sub>) and diphenyliodonium hexafluorophosphate (Ph<sub>2</sub>I<sup>+</sup>PF<sub>6</sub><sup>–</sup>). A feasible mechanism, as correlated
with optical absorption measurements, free energy changes (Δ<i>G</i>), and proton scavenging studies, involves formation of
exciplex by the absorption of light in the first step. Subsequent
electron transfer from excited C<sub>60</sub> or PS-C<sub>60</sub> to oxidizing salt yields radical cations of the fullerene derivatives.
Both radical cations and a strong Brønsted acid derived by hydrogen
abstraction initiate the cationic polymerization of a variety of monomers
