Iodonium Borate Initiators for Cationic Photopolymerization and Their Application in Radical-Induced Cationic Frontal Polymerization

Abstract

Iodonium antimonates and borates are well established initiators in the field of cationic photopolymerization and preferred substances for radical-induced cationic frontal polymerization (RICFP). Extensive research in the fields of ionic liquids and lithium ion battery electrolytes made many superacids based on the borate anions available. Cyanide-ligated borane B2 has lower molecular weight compared to state-of-the-art borates and is less expensive to synthesize from commercial starting materials. By comparing reactivity in the epoxy-based monomer bisphenol-A-diglycidylether, B2 outperforms all commercial systems in a broad range of temperatures with excellent epoxy group conversions of up to 95%. Besides its good performance as a cationic initiator, B2 is also capable of thermally and photochemically induced RICFP. Exceptional are transparent B2 specimens in contrast to the tested commercial systems, which are black. High reactivity, good frontal parameters, easy synthetic access, and sufficient pot life of formulations make cyanide-ligated iodonium borates a compelling alternative to current state-of-the-art initiators.