Charge transfer complexes (CTCs) with iodonium salts: Efficient initiators for single/two-photon polymerization

Abstract

Charge transfer complexes (CTCs), as a new type of photoinitiator system, exhibit excellent initiating abilities and are widely used in free radical polymerization. The reason is that it has safe photo or photo/thermal or dual initiator properties, which cannot be achieved by classical initiators. Thus, five novel iodonium salts (acceptors) and two amines (donors) capable of initiating thermal and photochemical polymerizations were investigated. The formations of the CTCs were assessed through their UV–visible (UV–vis) absorption spectra. The theoretical model study also attempted to show the relationship among the structure, reactivity, and efficiency of CTCs. Further explanation of the cause of this mechanism was provided by 1H NMR. The UV–vis photoinitiation ability of radical photopolymerization was also studied by real-time Fourier transform infrared spectroscopy and photo-DSC under LED@395–425 nm. The application of the newly developed initiating system in laser direct writing experiments at two-photon polymerization (780 nm) shows excellent spatial resolution performance. Such characteristic demonstrates that potential versatility can be applied in single/two-photon polymerization to manufacture high-precision materials.