The NIR-sensitized cationic photopolymerization of oxetanes in combination with epoxide and acrylate monomers

Abstract

A study involving NIR-sensitized cationic photopolymerization focused on a series of oxetanes exhibiting remarkable reactivities. A heptamethine cyanine carrying a cyclopentene moiety at the central position and an iodonium salt containing the aluminate [(Al(O-t-C₄F₉)₄)₄]⁻ served as the initiator system, which was combined with a high-power NIR-LED as the excitation source emitting at 805 nm with an intensity of 1.2 W cm⁻². Real-time FTIR analysis pursued under adiabatic conditions showed the good reactivities of the distinct oxetanes used in this study. The final conversion and reaction rates of OXT-03 depended on the concentration of the sensitizer rather than on the concentration of the iodonium salt. Moreover, hybrid photopolymerization based on free-radical and cationic photopolymerization used an oxetane monomer containing an –Si(OR)₃ moiety in combination with TMPTA at different ratios. The results obtained showed that when the ratio of TMPTA : GR-Si123 was 5 : 5, the free-radical polymerization rate of TMPTA was similar compared to the cationic polymerization rate of GR-Si123. The addition of TMPTA resulted in an improvement in the solubility of the initiator components in the mixture, while dissolution in neat GR-Si123 can be seen to be more or less as poor. This mixture of monomers containing cationic and radical polymerizable groups facilitated the formation of interpenetrating polymer networks (IPNs ). In addition, the use of an epoxide and acrylate ester resulted in similar accelerations of the cationic polymerization of oxetane in both UV and NIR-sensitized photopolymerization. DMA investigations revealed the tan δ data, which provided the respective glass transition temperature (T_g) data. Here, a TMPTA : GR-Si123 ratio of 5 : 5 resulted in the lowest T_g value.