Synthesis of hyperbranched copolyimides and their application as selective layers in composite membranes Original Research Article

Self-standing dense membranes from hyperbranched copolyimides based on (hexafluoroisopropylidene)diphthalic anhydride (6FDA), 1,3,5-tris(4-aminophenoxy)benzene (TAPOB) and 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) were successfully prepared and characterized for physicochemical properties. The synthesis involved the formation of hyperbranched poly(amic acid) precursors in the first step and their thermal imidization in the second step. Molar ratio of comonomers was 0.95:1 for 6FDA-TAPOB polyimide and 0.95:0.5:0.5 for 6FDA-6FpDATAPOB copolyimide. No gelation occurred during polymerizations if the concentration of resulting polymer was kept below 4 wt.%. Prepared polyimides showed moderate molecular weights (Mw ∼ 37,000), 6FDA-6FpDA-TAPOB copolyimides showed significantly broader polydispersity index (4.3) then for 6FDA-TAPOB poylimide (1.9). Both polymers exhibited similar glass transition temperatures (Tg ∼ 230°C) and 10 wt.% loss temperatures T10 ∼ 505°C).