Intrinsically Microporous Soluble Polyimides Incorporating Tröger’s Base for Membrane Gas Separation

Polyimides with intrinsic microporosity were readily prepared by introducing Tröger's base (TB) into the polymer backbone via polymerization between imide-containing diamines and dimethoxymethane (DMM). Two imide-containing diamines were prepared by reaction of 2,5-dimethyl-1,4-phenylenediamine (DPD) with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA). The resulting polyimides were readily soluble in common organic solvents, had good mechanical properties, with tensile strength in the range of 59–64 MPa and elongation at break of 5–17%, good thermal stability and extremely high glass transition temperatures (Tgs), up to 425 °C. The polyimides with incorporated TB units had high fractional free volume (FFV ≥ 0.215) resulting from poor chain-packing and exhibited significant microporosity and good gas transport properties. The novel polymer architecture in this study extends the development of polyimides with intrinsic microporosity for membrane-based gas separation.