Synthesis and Gas Permeation Properties of Spirobischromane-Based Polymers of Intrinsic Microporosity


Polymers of intrinsic microporosity (PIMs) possess molecular structures composed of fused rings with linear units linked together by a site of contortion so that the macromolecular structure is both rigid and highly non-linear. For PIM-1, which has previously demonstrated encouraging gas permeability data, the site of contortion is provided by the monomer 5,5',6,6'-tetrahydroxy-3,3,3',3' tetramethyl-1,1'-spirobisindane. Here we describe the synthesis and properties of a PIM derived from the structurally related 6,6’,7,7’-tetrahydroxy-4,4,4’,4’-tetramethyl-2,2’-spirobischromane and copolymers prepared from combination of this monomer with other PIM-forming biscatechol monomers, including the highly rigid monomer 9,10-dimethyl-9,10-ethano-9,10-dihydro-2,3,6,7- tetrahydroxyanthracene. Generally the polymers display good solubility in organic solvents and have high average molecular masses (Mw) in the range 80000-200000 g/mol and, therefore, are able to form robust, solvent-cast films. Gas permeability and selectivity for He, H2, N2, O2, CO2 and CH4 were measured for the polymers and compared to the values previously obtained for PIM-1. The spirobischromane-based polymers demonstrate enhanced selectivity for a number of gas pairs but with significantly lower values for permeability. The solubility coefficient for CO2 of two of the copolymers exceed even that of PIM-1, which previously demonstrated the highest value for a membraneforming polymer. Therefore, these polymers might be useful for gas or vapor separations relying on solubility selectivity.
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