Tuning the fraction free volume of hyperbranched 6FDA/TAPA polyimide membrane via DAM for enhanced gas separation performance

An effective strategy to optimize the gas separation performance of hyperbranched polyimide (hyper‐PI) membranes by tuning their average cavity sizes is reported. Triphenylamine (TAPA) and 4,4′‐(Hexafluoroisopropylidene) diphthalic anhydride (6FDA) were used to prepare the hyper‐PI membrane, and the transformation in free fraction volume (FFV) was realized by the addition of an extra B2‐type monomer, 2,4,6‐Trimethylbenzene‐1,3‐diamine (DAM). In hyperbranched networks, DAM, in conjunction with 6FDA, generates longer linear parts and reduces the density of dendritic architectures formed by TAPA. The conformational freedom of hyperbranched TAPA‐6FDA is restricted, and chain packing is hindered. The ratio of DAM:TAPA predominantly influences both the average cavity sizes and the FFVs of the membranes, leading to the variation in gas permeabilities. DAM5:TAPA1‐6FDA shows the best performance in both O2/N2 and CO2/N2 separations.