Microporous Polyimides from Ladder Diamines Synthesized by Facile Catalytic Arene–Norbornene Annulation as High-Performance Membranes for Gas Separation

We
synthesized a series of rigid ladder-type diamines from readily
available bromoanilines and norbornadiene in one step using facile
catalytic arene–norbornene annulation (CANAL). Polycondensation
of CANAL ladder diamines with 4,4′-(hexafluoroisopropylidene)­diphthalic
anhydride led to a series of microporous polyimides with different
degrees of rotational freedom around the imide linkages. CANAL-PIs
exhibited good solubility in a wide range of organic solvents, high
thermal stability with decomposition temperature above 450 °C,
high Brunauer–Emmett–Teller surface areas of ∼200–530
m2 g–1, and abundant micropore volume
with variable pore size distributions. Mechanically robust membranes
can be easily formed from CANAL-PIs and gave high gas permeabilities
and moderate gas-pair selectivities. CANAL-PIs had higher permeability
than and similar permselectivity to analogous PIs synthesized from
Tröger’s base and carbocyclic Tröger’s
base diamines under identical test conditions. CANAL-PIs also exhibited
relatively slow physical aging. These favorable properties and performance
make microporous polymers based on CANAL ladder motifs promising membrane
materials for gas separation.