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.
Keywords: cations; interpenetrating polymer network; near infrared; photopolymerization; weakly coordinating anion.
© 2020 The Authors. Published by Wiley-VCH GmbH.