Light gas and propene/propane permeabilities of copolymers of intrinsic microporosity containing highly rigid triptycene-like naphthopleiadene or spiropyrimidinone units

Polymers of intrinsic microporosity have been recognized as the potential solution for a number of challenging gas separation operations that require highly permeable and/or highly selective gas separation membranes. The possibility to tailor the transport properties by structural variation is a big feature of this class of polymers. Here we report the synthesis, characterization and gas transport properties of a series of PIM-1 based copolymers with accessible naphthopleiadene and spiropyrimidinone units. The copolymers with 10% of the comonomer were all soluble in CHCl3 and formed good films at room temperature. All copolymers outperformed PIM-1 in the Robeson plots with an increase of either permeability, selectivity, or sometimes both for the separation of several industrially relevant gas pairs, such as CO2/CH4, CO2/N2, O2/N2 and H2/CH4. Aging generally leads to a gradual increase in selectivity at the expense of permeability. A feasibility study for propene/propane separation revealed that the high size selectivity of these PIMs results in a very low diffusion coefficient of these relatively large molecules, 2-3 orders of magnitude lower than the standard light gases, and with significant difference also between propene and propane. The possibility to measure diffusion selectivity besides permselectivity provided important information on the origin of the C3H6/C3H8 ideal selectivity, which increases from 4.2 for PIM-1 to over 18 for aged PIM-TDHP10 and confirms the high potential of microporous polymers in this separation.