Chemistry of Materials
Communication
(5) Ito, K.; Nishimura, M.; Sashio, M.; Tsunooka, M. J. Polym. Sci.,
Part A: Polym. Chem. 1994, 32, 1793.
3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, and 9H
(hardest). Surprisingly, the coating film showed a level of 3H
after 365 nm light irradiation with an exposure dose of 1000
mJ/cm2 without postexposure baking, which is quite enough
for practical use. This means that the anionic UV curing
material sensitized with 4c is highly sensitive, taking into
account the fact that conventional anionic UV curing materials
were cured by heating at 150−200 °C for ca. 1 h after UV
irradiation. By contrast, coating films showed a level lower than
6B when we use 4e, which generates cyclohexylamine (CyA).
This is because the basicity of CyA is too weak to induce
deprotonation reactions of thiol monomer 6.
Radical UV curing materials that are well established in the
marketplace have drawbacks because of high volume shrinkage
and oxygen inhibition. Our anionically cured film showed high
transparency and no volume shrinkage, in contrast to a
conventional radical UV curing system, which showed large
volume shrinkage, as given in Figure 5.22
(6) Cameron, J. F.; Frec
12925.
́
het, J. M. J. J. Am. Chem. Soc. 1996, 118,
(7) Nishikubo, T.; Kameyama, A.; Toya, Y. Polym. J. 1997, 29, 450.
(8) Kaneko, Y.; Sarkar, A. M.; Neckers, D. C. Chem. Mater. 1999, 11,
170.
(9) Jensen, K. H.; Hansen, J. E. Chem. Mater. 2002, 14, 918.
(10) Blanc, A.; Bochet, C. G. J. Am. Chem. Soc. 2004, 126, 7174.
(11) Dietliker, K.; Misteli, K.; Studer, K.; Lordelot, C.; Carroy, A.;
Jung, T.; Benkhoff, J.; Sitsmann, E. Proc. RADTECH UV&EB Technical
Conference 2008 2008, 10.
(12) Sun, X.; Gao, J. P.; Wang, Z. Y. J. Am. Chem. Soc. 2008, 130,
8130.
(13) Costanzo, L. L.; De Guidi, G.; Condorelli, G.; Cambria, A.;
Fama, M. Photochem. Photobiol. 1989, 50, 359.
(14) A preliminary report: Arimitsu, K.; Endo, R. J. Photopolym. Sci.
Technol. 2010, 23, 135.
(15) A preliminary report: Arimitsu, K.; Kushima, A.; Endo, R. J.
Photopolym. Sci. Technol. 2009, 22, 663.
(16) Blake, J. A.; Gagnon, E.; Lukeman, M.; Scaiano, J. C. Org. Lett.
2006, 8, 1057.
(17) Nichols, M. E.; Seubert, C. M. Proc. Am. Chem. Soc. Div. Polym.
Mater. Sci. Eng. Symp. 2009, 101, 1141.
(18) Seubert, C. M.; Nichols, M. E. J. Coat. Technol. Res. 2010, 7, 615.
(19) Φ was determined according to the literature.3
(20) A UV-curable resin solution was prepared by dissolving 0.50 g
(1.2 × 10−3 mol) of 5, 0.67 g (1.2 × 10−3 mol) of 6, and 4c (10 mol %
relative to 5) in methanol. The solution was coated on glass plates and
prebaked at 60 °C on a hot stage for 30 s to give a film. UV curing was
achieved by exposing the films to 365 nm light. The pencil hardness of
the films was evaluated by scratching UV-cured coatings with pencils
according to JIS K5400.
(21) JIS K5400 defined by Japanese Industrial Standards is a simple
method to test the scratch hardness of coatings. In this test, pencils in
a range of 6B to 9H hardness grade are used. The pencil is moved
scratching over the surface of the coating at a 45° angle with a constant
pressure.
Figure 5. Comparison of volume shrinkage between anionic UV
curing and radical UV curing systems.
(22) An anionic UV-curable resin solution was prepared by dissolving
0.50 g (1.2 × 10−3 mol) of 5, 0.67 g (1.2 × 10−3 mol) of 6, and 4c (10
mol % relative to 5) in methanol. The solution was coated on an OHP
sheet and prebaked at 60 °C on a hot stage for 30 s to give 14 μm-
thick film. UV curing was achieved by exposing the film to 365 nm
light (10 J/cm2). A radical UV-curable resin solution was prepared by
dissolving 1 g of PETA and 5 wt % of Irgacure 819 in methanol. UV
curing was achieved in a similar manner.
In conclusion, we present novel photobase generators (3 and
4) based on photodecarboxylation reactions. These photobase
generators can be easily prepared by mixing ketoprofen (1) or
xanthone acetic acid (2) with corresponding superbases. We
have also developed a novel anionic UV curing system without
postexposure baking, which consists of an epoxy monomer, a
thiol monomer, and the photosuperbase generator.
ASSOCIATED CONTENT
* Supporting Information
Experimental methods and preparation of photobase gen-
erators. This material is available free of charge via the Internet
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S
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
REFERENCES
(1) Ito, H. Adv. Polym. Sci. 2005, 172, 37.
(2) Crivello, J. V. J. Coat. Technol. 1991, 63, 35.
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(3) Cameron, J. F.; Frec
4303.
(4) Frec
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het, J. M. J. J. Am. Chem. Soc. 1991, 113,
́
het, J. M. J. Pure Appl. Chem. 1992, 64, 1239.
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dx.doi.org/10.1021/cm4022485 | Chem. Mater. 2013, 25, 4461−4463