Effects of metal acetate addition on the gas separation properties of polymers of intrinsic microporosity PIM-1 and PIM-Py

Gas separation properties are reported for self-standing polymer of intrinsic microporosity (PIM) films after addition of palladium (II) acetate or iron (II) acetate by solid state or liquid state mixing. Membranes, with thicknesses in the range 35–55 μm, were prepared from three high molar mass PIMs, two different branched versions of the much-reported PIM-1 (PIM-1a and PIM-1b) and of PIM-Py. Addition of either Fe(OAc)2 or Pd(OAc)2 to all three PIMs led to a reduction in permeability and increase in selectivity, but the permeability reduction was much greater for Pd(OAc)2, which is able to interact with branch points in the PIM and crosslink the polymer. CO2/CH4 selectivity of membranes containing Pd(OAc)2 was poor upon aging, especially after solid state addition to the PIM-1 polymers, for which CO2 permeabilities dropped to below 200 Barrer after 85 days. Hydrogen permeability and H2/N2 selectivity of membranes containing Pd(OAc)2 did more closely follow conventional permeability/selectivity trade off upon aging. This illustrates the profound differences that can arise in gas permeation properties and aging behaviour from variations in chemical structure and macromolecular characteristics, and from the addition of metal acetates that interact with the polymer in different ways.