Synthesis and properties of new aromatic polyimides containing spirocyclic structures

The synthesis of three novel aromatic polyimides (PIs) containing spiro units is described. These PIs are soluble at room temperature in most common organic solvents, facilitating their processability. Additionally, they are highly thermally stable, with thermal decomposition temperatures (T_d10%) over 500 °C, and had moderately high T_g values between 230 and 265 °C. Robust self-standing thin films were prepared from these polyimides, via the solution casting method, which were suitable for gas transport measurements. The relatively low permeability and selectivity of these PIs, as compared to Polymers of Intrinsic Microporosity (PIMs) that also contain spirocyclic structures, demonstrate the importance of restricting rotation within the polymer chain, which is a key structural feature of the PIMs.