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.