NIR-Sensitized Cationic and Hybrid Radical/Cationic Polymerization and Crosslinking

NIR-sensitized cationic polymerization proceeded with good efficiency, as was demonstrated with epoxides, vinyl ether, and oxetane. A heptacyanine functioned as sensitizer while iodonium salt served as coinitiator. The anion adopts a special function in a series selected from fluorinated phosphates (a: [PF₆ ]^- , b: [PF₃ (C₂ F₅ )₃ ]^- , c: [PF₃ (n-C₄ F₉ )₃ ]^- ), aluminates (d: [Al(O-t-C₄ F₉ )₄ ]^- , e: [Al(O(C₃ F₆ )CH₃ )₄ ]^- ), and methide [C(O-SO₂ CF₃ )₃ ]^- (f). Vinyl ether showed the best cationic polymerization efficiency followed by oxetanes and oxiranes. DFT calculations provided a rough pattern regarding the electrostatic potential of each anion where d showed a better reactivity than e and b. Formation of interpenetrating polymer networks (IPNs) using trimethylpropane triacrylate and epoxides proceeded in the case of NIR-sensitized polymerization where anion d served as counter ion in the initiator system. No IPN was formed by UV-LED initiation using the same monomers but thioxanthone/iodonium salt as photoinitiator. Exposure was carried out with new NIR-LED devices emitting at either 805 or 870 nm.