Synthesis, characterization and hydrolytic stability of poly (amic acid) ammonium salt

A series of new poly (amic acid) ammonium salt (PAAS) precursors were prepared by incorporating different amounts of triethylamine (TEA) into terpolymer polyamic acid (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4'-oxydianiline (ODA) and p-phenylenediamine (PDA) in dimethylacetamide (DMAc). Then, the PAAS films were made by casting their solutions onto glass plates followed by the evaporation of the solvent. The chemical structure of PAAS films was confirmed by 1H NMR and FTIR spectroscopy. Mechanical properties, intrinsic viscosities and solubility of PAAS precursors were examined, respectively. It was found that the intrinsic viscosity of PAA solution obviously decreased with storage time during 30 days, while no distinct changes were observed in the intrinsic viscosity of the PAAS (the mole ratio of TEA/repeating unit of PAA = 2/1) solution after 90 days. The results suggested that hydrolytic stability of the PAAS films was significantly improved as compared with that of PAA film due to the polyelectrolyte structure of PAAS. Moreover, the thermal and mechanical properties of polyimide (PI) films prepared from PAAS precursors were also investigated, respectively.