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

Abstract

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′-tetramethylbenzidine, 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.