Polymer Nanofilms with Engineered Microporosity By Interfacial Polymerisation for Molecular Separations in Organic Solvent

Molecular design of microporous materials has led to new pathways for improving the molecular differentiation achieved by separation membranes used for gas separation, water desalination, and separations in chemical and pharmaceutical synthesis. Recently developed microporous materials, including polymers of intrinsic microporosity (PIMs), metal organic frameworks, and graphene oxide, all have micropores of less than 1 nm, and so are relevant for developing molecular separating membranes. This paper focuses in membranes for Organic Solvent Nanofiltration (OSN) [1]. lPIMs are a new class of rigid polymers with high free volume, which results from inefficient polymer packing. Several efforts to make dip-coated TFC-PIMs membranes solvent resistant have been reported, including photo-crosslinking, blending with thermally reactive polymers and chemical crosslinking.

In this work we fabricated ultra-thin highly crosslinked PIM-like nanofilms down to 20 nm in thickness by interfacial polymerization. To engineer permeance and selectivity, we sought to design and control the polymer nanofilm structure at a molecular level by incorporating contorted monomers during the interfacial reaction. This results in enhanced microporosity and higher interconnectivity of intermolecular network voids, as rationalised by molecular simulations. Composite membranes comprising these nanofilms with enhanced microporosity fabricated in-situ on crosslinked polyimide UF membranes show outstanding separation performance in organic solvents, with up to two orders of magnitude higher solvent permeance than membranes fabricated with nanofilms made from non-contorted, planar monomers and membranes reported in the literature [2]. A new organic solvent Robinson upper bond has been drawn to show outstanding perm-selective performance in organic solvents.

By tuning cavity width in the range of 5 ~ 10 Å, the molecular separation performances were further improved for driven nanofiltration. Superior selectivities of the micropore nanofilms was further investigated by molecular dynamic simulation, which showed the interplay of pore wall interaction and entrance sieving.