(498d) Engineering Highly Microporous Polymer Nanofilms By Interfacial Polymerization of Rigid Units for Ultrafast Organic Solvent Nanofiltration

High-permeance membranes at a desired molecular weight cut-off (MWCO) are key elements for organic solvent nanofiltration (OSN). Polymers of intrinsic microporosity (PIMs) are of particular interest for this application due to their high solvent permeability coupled with abundant micropores (pore size < 20 Å). However, PIM-based thin-film composite (TFC) membranes have several drawbacks, including accelerated physical aging, defect formation, and limited solvent resistance. To circumvent these issues, we report a method to form highly microporous and crosslinked polymer nanofilms prepared by a facile interfacial polymerization technique. Two structural monomers for PIMs – a Tröger's base diamine (TBD) and spirobifluorene (SBF) acyl chloride – were synthesized and investigated as building blocks for crosslinked polyamide TFC membranes. Remarkably, the TFC membrane fabricated by these PIM units through interfacial polymerization (i.e., TBD-SBF) exhibited more than two orders of magnitude higher solvent permeance (e.g., acetone permeance = ~100 LMH/bar) with moderate MWCO (~630 g/mol) compared to conventional MPD-TMC counterparts, which outperforms all reported polymer-based OSN membranes. Detailed characterization reveals that the enhanced microporosity enabled by selection of the rigid PIM monomers coupled with the benefits of forming ultrathin (~20 nm) membranes through interfacial polymerization enables ultrafast solvent transport in the TBD-SBF nanofilms. These findings demonstrate a means to leverage micropore-generating features with interfacial polymerization for promising applications in OSN.