High-Pressure Reactivity of Triptycene Probed by Raman Spectroscopy
The high-pressure reactivity of caged olefinic carbons and polyatomic aromatic hydrocarbons (PAHs) are of interest because of their ability to produce unique C-H networks with varying geometries and bonding environments. Here, we have selected triptycene to explore the creation of pores via high-pressure polymerization. Triptycene has internal free volume on a molecular scale that arises due to its paddle wheel-like structure, formed via fusion of three benzene rings via sp3-hybridized bridgehead carbon sites. At 25 GPa and 298 K, triptycene polymerizes to yield an amorphous hydrogenated carbon, with FTIR indicating an sp3 C-H content of approximately 40%. Vibrational spectroscopy conclusively demonstrates that triptycene polymerizes via cycloaddition reactions at the aromatic sites via a ring opening mechanism. The bridgehead carbons remain intact after polymerization, indicating the rigid backbone of the triptycene precursor is retained in the polymer, as well as molecular-level (∼1-3 Å) internal free volume. High resolution transmission electron microscopy, combined with dark field imaging, indicates the presence of ∼10 nm voids in the polymer, which we attribute to either polymeric clustering or a hierarchical tertiary porous network. Creation of a polymerized network that retains internal voids via high-pressure polymerization is attributed to the presence and retention of the bridgehead carbons.
P. C. Ray et al., "High-Pressure Reactivity of Triptycene Probed by Raman Spectroscopy," Journal of Physical Chemistry B, vol. 120, no. 42, pp. 11035 - 11042, American Chemical Society (ACS), Sep 2016.
The definitive version is available at https://doi.org/10.1021/acs.jpcb.6b05120
Chemical and Biochemical Engineering
United States. Department of Energy. Office of Basic Energy Sciences
Keywords and Phrases
Amorphous carbon; Aromatic compounds; Aromatic hydrocarbons; Cycloaddition; Fourier transform infrared spectroscopy; Free volume; Polycyclic aromatic hydrocarbons; Polymerization; Amorphous hydrogenated carbon; Bonding environment; Cycloaddition reaction; Dark field imaging; High-pressure reactivity; Molecular levels; Molecular scale; Porous networks; High resolution transmission electron microscopy
International Standard Serial Number (ISSN)
Article - Journal
© 2016 American Chemical Society (ACS), All rights reserved.
01 Sep 2016