Ultra-Thin Composite Carbon Membranes from a Polymer of Intrinsic Microporosity Precursor

Carbon molecular sieve (CMS) membranes have attracted significant attention due to their ability to break the polymer gas separation trade-off relationships (upper bounds) for several technologically important gas pairs (e.g. O₂/N₂ or CO₂/CH₄). However, to realize their industrial potential CMS membranes will need to be fabricated as thin, supported, defect-free films with thicknesses in the range of several micrometers or less. This poses several potential challenges, for instance, the need to avoid development of pin-holes or the lesser known issues with deviation from bulk properties as a result of film confinement to the substrate (nano-confinement effects).

While CMS thin-film composite membranes are predominantly made by pyrolysis of high-free-volume traditional glassy polymers (e.g. Matrimid, 6FDA-DABA-derivatives) the use of polymers of intrinsic microporosity (PIMs) as precursor has not yet been explored.

In this work, we investigated the fabrication and gas separation properties of thin-film composite CMS membranes made from a PIM precursor pyrolyzed directly on a highly porous inorganic support. Changes in film thickness and density following inert atmosphere pyrolysis were evaluated using spectroscopic ellipsometry. Thin-film CMS are shown to significantly deviate from bulk both in terms of their behavior during pyrolysis and the resulting separation performance.