Ionic hyper-cross-linked porous polymer networks with achiral and chiral pyridinium-type segments

A new type of ionic porous polymer networks (PPNs) is reported containing (i) N-alkyl pyridinium bromide ionic groups and (ii) a hyper-cross-linked scaffold based on polyacetylene (polyene) chains the rigidity of which contributes to the permanent porosity the PPNs. The ionic PPNs were prepared by a combination of chain-growth polymerization of acetylenic monomers and quaternization reactions of pyridine and alkyl bromide moieties. The wide variability of this synthetic concept enabled the preparation of covalently diverse PPNs with ionic groups located either in the pendant groups or in the knots of the networks, as well as the preparation of PPNs with chiral ionic groups. The content of ionic groups in PPNs ranged from 1.5 to 4.2 mmol/g, and the BET area was from 67 to 744 m2/g. The mode of quaternization used (prepolymerization or postpolymerization) controlled the contribution of micropores and mesopores to the porosity of the ionic PPNs. The polyacetylene ionic PPNs were active as heterogeneous organocatalysts (applied without a cocatalyst) for the cycloaddition of CO2 to styrene oxide yielding styrene carbonate as the only product (up to 96 %). PPNs with chiral ionic groups showed potential for enantioselective catalysis of this reaction. The catalytic activity was controlled by the accessibility of pyridinium active centres for the substrate molecules. Ionic PPNs prepared were also efficient in reversible water vapour capturing and releasing (capacity up to 361 mg/g at 298 K and RH = 90 %). Both surface adsorption and capillary condensation of H2O contributed to the water vapour capture on reported PPNs.