On the Use of Bis(cyclopentadienyl)titanium(IV) Dichloride in Visible-Light-Induced Ring-Opening Photopolymerization

A titanocene derivative (bis(cyclopentadienyl)titanium(IV) dichloride Cp 2 TiCl 2 ), for visible light induced polymerization of cationic resins working through a free radical promoted process is presented. This new photoinitiating system is based on the Cp 2 TiCl 2 free radical initiator, a silane (tris(trimethylsilyl)silane: TTMSS), and an onium salt (diphenyliodonium hexafluorophosphate: Ph 2 I + ) and appears suitable under long wavelength irradiation (λ > 400 nm). The polymerization reaction is highly efficient in aerated conditions (almost 100% conversion) and dramatically better than in laminate. The system works under exposure to a Xe lamp, a diode laser or a household LED bulb. The mechanisms are investigated by ESR experiments. The specific role of the generated free radicals is highlighted.