CO2-selective vinyl-addition polymers from nadimides: Synthesis and performance for membrane gas separation

Abstract

The polymers, combining saturated rigid main chains and imide moieties, were synthesized through vinyl-addition polymerization of substituted nadimides (VAP polymers) and assessed for the first time as potential membrane materials for gas separation. Previously difficult-to-access high molecular weight VAP polymers were readily prepared in good yields in the presence of (NHC)Pd-complexes (NHC – N-heterocyclic carbene ligand). As monomers, various racemic and chiral nadimides with the alkyl, aryl, fluoroaryl, and α-amino acid’ moieties were used. Thin polymeric membranes from VAP polymers exhibited desirable mechanical properties and good thermal stability. Related metathesis polymers from the nadimides were also obtained for the properties comparison. Pure (He, H2, O2, N2, CO2, CH4) and mixed gases (CO2/N2, CO2/CH4) permeation was investigated in detail for the prepared VAP polymers with different nature of imide-fragments. Valuable structure-property relationships were established, and it was found that VAP polynorbornene with fluoroaryl-groups in imides moieties exhibited the combination of high CO2 permeability with attractive CO2/N2 and CO2/CH4 selectivities. For the separation of the industrial relevant gas mixture, CO2/CH4, this polymer is above the 2008 upper bound for single gas separation and the 2018 upper bound for mixed-gas separation. With CO2 permeability of >1300 Barrer and CO2/CH4 separation selectivity of 29, the performance of the polymer exceeded that of other VAP and metathesis nadimide polymers.