Highly permeable and selective membranes are desirable for energy-efficient gas and liquid separations.
Microporous organic polymers have attracted significant attention in this respect owing to their high
porosity, permeability, and molecular selectivity. However, it remains challenging to fabricate selective
polymer membranes with controlled microporosity which are stable in solvents. Here we report a new
approach to designing crosslinked, rigid polymer nanofilms with enhanced microporosity by
manipulating the molecular structure. Ultra-thin polyarylate nanofilms with thickness down to 20 nm
were formed in-situ by interfacial polymerisation. Enhanced microporosity and higher interconnectivity
of intermolecular network voids, as rationalised by molecular simulations, are achieved by utilising
contorted monomers for the interfacial polymerisation. Composite membranes comprising polyarylate
nanofilms with enhanced microporosity fabricated in-situ on crosslinked polyimide ultrafiltration
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 noncontorted
planar monomers.