Low-temperature synthesis and gas transport properties of novel contorted hyperbranched polyimides containing binaphthyl structures

•High performance contorted HBPIs containing binaphthyl structures were prepared.•Low-temperature synthesis technique was adopted aiming to avoid the risk of gelation.•Designed HBPIs had high Tg, excellent thermal stability, and their PAA had high Mn.•Larger amount of contorted moieties enhances the gas permeabilities significantly. In this study, a series of novel contorted hyberbranched polyimides (HBPIs) were successfully prepared based on commercially available monomers 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 1,1′-binaphthyl- 2,2′-diamine (BNDA), and 1,3,5-tris(4-aminophenyl) benzene (TAPB), and the BNDA comonomer was used to create the contorted moieties in polymer backbone. Experimental results demonstrated that all the prepared HBPIs possessed high glass transition temperatures (Tg = 309~325 °C), excellent thermal stability (Td,5% = 489~503 °C), and their PAA precursors had high number-averaged molecular weights (Mn = 2.9 × 104~5.6 × 104 g/mol). Furthermore, the effect of the degree of contorted moieties in HBPIs changing by the different molar ratios of TAPB:BNDA on polymeric fractional free volumes (FFV) and gas transport properties was systematically investigated. As a result, with the increasing content of BNDA monomer, the gas permeabilities of HBPI membranes were significantly increased. For example, the CO2 and O2 permeabilities of HBPI membrane with the molar ratio of TAPB:BNDA = 4:6 were respectively about 2.8 and 3.2 times higher than that of HBPI membrane without any contorted moieties. Besides, it also maintained reasonable selectivities for CO2/CH4 (~46.3) and O2/N2 (~5.7). These encouraging results were related to the synergetic effects of incorporating contorted sites and improving polymer rigidity by using monomers BNDA and TAPB in copolymerization reaction. Furthermore, no gelation occurred during polymerizations due to the adopted low-temperature synthesis technique that can effectively avoid the high local concentration of the added 6FDA monomer. This work provides a new insight to produce high performance contorted HBPIs containing binaphthyl structures without risk of gelation and also shows a potential application in gas separation.