Synthesis and Gas Permeability of Chemically Cross‐Linked Polynorbornene Dicarboximides Bearing Fluorinated Moieties

This work reports on the synthesis of a novel bifunctional norbornene dicarboximide monomer (HFDA) based on 4,4-(hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline and its application as a cross-linking agent in the ring-opening metathesis polymerization (ROMP) with N-3-trifluoromethylphenyl-exo,endo-norbornene-5,6-dicarboximide (mCF(3)) employing the Grubbs 2nd generation catalyst (I) and cis-1,4-diacetoxy-2-butene as a chain transfer agent (CTA) to yield a series of soluble nonlinear highly branched chains polymers with increasing degree of cross-linking. A comparative study of gas transport in membranes based on these cross-linked polynorbornene dicarboximides is performed and the gases studied are hydrogen, oxygen, nitrogen, carbon dioxide, methane, ethylene, and propylene. It is found that cross-linking increases the gas permeability, leads to the highest separation factor reported to date for the H-2/C3H6 mixture in this kind of polymers, and also enhances the CO2 plasticization resistance up to 14 atm upstream pressure. The chemical cross-linking approach employed in this research is an effective tool to enhance gas transport properties for dense polynorbornene dicarboximide membranes.