Synthesis and properties of highly gas permeable poly(amide‐imide)s

Seven dicarboxylic acids containing one or two preformed imide rings were prepared by condensation of trimellitic anhydride with 3‐amino‐4‐methylbenzoic acid or with the diamines 2,4,6‐trimethyl‐1,3‐phenylenediamine, 3,3′‐dimethoxybenzidine, 3,3′,5,5′‐tetramethyl‐benzidine, 3,3′‐dimethyl‐1,1′‐binaphthalene or by condensation of 2,2‐hexafluoroisopropylidenebis(phthalic acid anhydride) (6FDA) with 2 mol of 3‐aminobenzoic acid or 3‐amino‐4‐methylbenzoic acid. Polycondensation was performed directly in N ‐methyl‐2‐pyrrolidone (NMP)/triphenyl phosphite/lithium chloride with oxydianiline, 2,2‐bis(4‐aminophenyl)‐perfluoropropane or 3,3′,5,5′‐tetramethylbenzidine. All the resulting polymers are soluble in NMP, some in tetrahydrofuran (THF) and could be cast to transparent, flexible and tough films. The helium permeability as a probe for diffusivity improves with increasing fluorine content and non‐linearity in the repeating unit.