High-Pressure Reactivity of Triptycene Probed by Raman Spectroscopy

Abstract

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.

Department(s)

Chemical and Biochemical Engineering

Sponsor(s)

United States. Department of Energy. Office of Basic Energy Sciences

Comments

Funding for this work was provided by the US Department of Energy(DOE) Basic Energy Sciences under Grant No. DE-FG02-09ER466556 and DE-SC0002157.

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)

1520-6106

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2016 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Sep 2016

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