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

Abstract 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 ( $\overline {M} _{{\rm w}} $ ) in the range 80 000–200 000 g · mol −1 and, therefore, are able to form robust, solvent‐cast films. Gas permeability and selectivity for He, H 2 , N 2 , O 2 , CO 2 , and CH 4 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 CO 2 of two of the copolymers exceed even that of PIM‐1, which previously demonstrated the highest value for a membrane‐forming polymer. Therefore, these polymers might be useful for gas or vapor separations relying on solubility selectivity. magnified image