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. DAM(5):TAPA(1)-6FDA shows the best performance in both O-2/N-2 and CO2/N(2 )separations.