Three soluble and processable polyimides (PIs) were prepared in high yield from imide-containing diamines via Tröger’s Base (TB) polymerization reactions using dimethoxymethane (DMM). The three novel imide-containing diamines were easily synthesized from a commercial diamine precursor, 2,6-diaminotoluene, and three commercially available dianhydrides. The corresponding membranes had fractional free volume (FFV) values in the range of 0.170–0.200, good mechanical, thermal and gas transport properties, which were correlated with the polymer chain structures. The incorporation of TB units into the PI backbone improved the gas transport performance. The TB-based polyimide membrane from BTDA had a CO2 permeability of 19.6 Barrer, an elongation at break of 9.0%, and a tensile strength of 114.2 MPa, suggesting better properties as gas separation membranes than Matrimid® polyimide from the same BTDA.