Figure 18 Schematic diagram of the preparation of the cardanol-based and eugenol-based thiol−ene polymer networks.[70]
Liu et al.[1] synthesized a series of novel coumarin-based oxime ester PIs which could effectively induce thiol-ene click photopolymerization under irradiation at 450 nm LED source, the chemical structures of the oxime ester (O-3, O-3F, O-3O and O-4), pentaerythritol tetra (3-mercaptopropionate) (PETMP), 1,7-octadiyne (ODY), triallyl isocyanurate (TAIC), triallyl cyanurate (TAC) and pentaerythritol triallyl ether (APE) used in the photopolymerization researches are displayed in Figure 19. The photopolymerization kinetics results show that the conversions of thiols and C=C bonds can reach more than 80% initiated by O-3, and fast rate and high conversion of the thiol (70%) and alkynyl (80%) indicate that O-3 can be used for the efficient thiol–yne photopolymerization. Besides, O-3/thiol–ene systems exhibit excellent photobleaching properties, which is favorable for light penetration. Therefore, the novel coumarin-based oxime ester O-3 can be used as visible light PI with enhanced performance in various thiol-based click photopolymerization.
Figure 19 Structures of the oxime ester PIs, mercaptan and monomers used in the photopolymerization.[1]
He et al,[79] designed a novel click lithography strategy based on the rapid thiol−ene click reaction to realize ultraefficient nanofabrication, the schematic illustration of thiol−ene reaction and click lithography are displayed in Figure 20. First of all, this work prepared a multialkene-functionalized zirconium (Zr)-containing MOC with a molecular size of ∼1.6 nm, and the material exhibits ultrahigh alkene density and extremely small component size, which is conducive to achieving high sensitivity and high resolution of the thiol−ene reaction. Next, this novel method enables high-contrast patterning of metal-containing nanoclusters at low deep-ultraviolet exposure dose(e.g., 7.5 mJ cm–2), which is 10–20 times lower than the dose used in the photoacid generator-based photoresist system. At the same time, 45 nm dense patterns were obtained at low dose using electron beam lithography, revealing the great potential of this method for high-resolution patterning.