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 ((M) over bar (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, 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 membrane-forming polymer. Therefore, these polymers might be useful for gas or vapor separations relying on solubility selectivity.