Understanding the Topology of the Polymer of Intrinsic Microporosity PIM-1: Cyclics, Tadpoles, and Network Structures and Their Impact on Membrane Performance

The synthesis of PIM-1 is reported from step-growth polymerizations of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane with the commercially cheaper monomer, tetrachloroterephthalonitrile. Nitrogen-purged polymerizations (100-160 °C) were quenched after a monitored increase in viscosity. A combination of multiple detector size exclusion chromatography, nuclear magnetic resonance, matrix-assisted laser desorption/ionization-time of flight (MALDI TOF) mass spectrometry, dynamic light scattering, and elemental analysis was used to elucidate significant structural differences (cyclic, branched, tadpole, extended, and network topologies) in the polymers produced under different conditions. A significant proportion of the apparent surface area (up to 200 m2 g-1) associated with PIM-1 can be attributable to whether its contorted polymer chains in fact link to form cyclic or other nonlinear structures. Membranes cast from solutions of polymer samples containing higher branching and network contents exhibited higher gas pair selectivities (CO2/CH4 and CO2/N2), above the Robeson 2008 upper bound. A toolbox approach to the characterization and production of topologically different PIM-1 samples has been developed which can be used to tune membrane performance for gas separation and other applications.