posted on 2024-01-10, 19:41authored bySulaiman
O. Lawal, Kenta Watanabe, Ryohei Uchino, Norihiro Moriyama, Hiroki Nagasawa, Toshinori Tsuru, Masakoto Kanezashi
Polyhedral
oligomeric silsesquioxanes (POSSs) are a promising family
of regularly structured silsesquioxanes with resilient cage-like configurations
and exterior edges that can be functionalized with various organic
groups. In this study, POSS was functionalized with a polyimide–phenylene
(PI–Ph) unit, which yielded POSS–PI–Ph to fabricate
carbonized-POSS membranes (denoted as carbon-POSS) via inert pyrolysis.
Replacing some PI–Ph units with norbornene (NB) increased the
amount of residual carbon formed in the carbon-POSS structure. X-ray
photoelectron spectroscopy and 29Si nuclear magnetic resonance
analysis revealed that residual sp2-hybridized carbon atoms
were connected to the POSS cage after pyrolysis at 700 °C. Analysis
of single-gas permeation at 200 °C with the carbon-POSS membranes
pyrolyzed at different temperatures (200–800 °C) indicated
that the permeance of all investigated gases (He, H2, CO2, N2, CH4, CF4, and SF6) increased with increasing membrane pyrolysis temperature.
Notably, the early onset of the decline in permeance of large-molecule
gases such as CF4 and SF6 at 600 °C ensured
a high N2 permeance and ideal N2/SF6 selectivity of 10–6 mol m–2 s–1 Pa–1 and 100, respectively. Overall,
this study demonstrates the feasibility of preparing high-performance
carbon-POSS-derived membranes by optimizing the NB functionality and
the POSS content of the hybrid copolymer precursor.