Poster Presentation 4
Development of new lignin-based polymers via photoredox
catalyzed thiol-ene click reaction
Hailing Liu, Hoyong Chung
Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University,
Tallahassee, Florida, USA
Abstract
Most commercial lignins are produced by treatment of sulfur containing chemical reagents. Therefore, it is
reasonable to suppose that the produced lignin has thiol groups in the structure. However, there has been no
systematic/scientific characterization of thiol group contents in a commercial lignin. In this report, we present
strong evidence of the existence of thiol in lignin using a fluorometer as shown in Figure 1. The emission
spectra in Figure 1 demonstrate typical emission spectra of thiol-conjugated N-1-pyrenylmaleimide. Pristine
lignin without conjugation reveal no emission as shown in blue dotted line (Blue dotted line is overlaid on red
dotted line with no intensity.). This spectrometry result clearly indicates that commercial lignin contains thiol
group, and the thiol can be used for diverse chemical modification.1
Based upon the thiol group discovery, we performed covalent bond forming integration methods (thiol-ene
click reaction) between lignin and a petroleum-based polymer, poly(acrylic acid) in the presence of photoredox
catalysts, Ru(bpy)3Cl2.2 The photo activated thiol-ene reaction needs a very small amount of the photoredox
catalyst—as small as 0.25 mol%—and those reactions can occur in a wide range of solvents, even in water.
Also, the photoredox catalysts can be activated by a visible sunlight wavelength range, blue light irradiation
(λmax = 460 nm) as shown in Figure 2.
Figure 1. Emission spectra of lignin
(solid line) before and (dashed/dotted
line) after reaction with N-1pyrenemaleimide.
Figure 2. A scene of
photoredox catalyzed lignin
modification under sunlight.
References
1.
Wu, C.-W.; Yarbrough, L. R.; Wu, F. Y. H. Biochemistry 1976, 15, (13), 2863-2868.
2.
Xu, J.; Boyer, C. Macromolecules 2015, 48, (3), 520-529.
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