Synthesis of soluble and thermally stable polyimides with phthalimide as pendent group from pyridine-containing triamine

We report the design and synthesis of a novel pyridine-containing triamine monomer, 2,6-bis(4-aminophenyl)-4-(4-aminophenoxy)pyridine (BAAP), through combining the nucleophilic aromatic substitution with modified Chichibabin reaction and hydrazine hydrate reduction. Based on it, a novel three-step route was applied in order to obtain a series of new polyimides, containing phthalimide as pendent group and pyridine moieties in main chains. The three-step route consisted of terminating the triamine by incorporating phthalic amic acid as pendant, ring-opening polymerization to form poly(amic acid)s and further chemical imidization to acquire polyimides. Nuclear Magnetic Resonance Spectroscopy (¹H-NMR) was used for chemical structural characterization, and the results indicated the various forms of BAAP and branched structure units in the obtained polyimides. The morphology structures of the polyimides were evaluated by X-ray diffraction patterns, and the d-spacing values were found in the range of 4.14–4.65 Ǻ. Most of the resulting polyimides were soluble in polar aprotic solvents, such as NMP, DMF, DMAc, DMSO, and so on. Meanwhile, the polyimides exhibited excellent thermal stability, with the decomposition temperature at 5 and 10 % weight loss temperatures in the ranges of 399.1–461.1 °C and 481.1–566.9 °C, respectively. The polyimides, based on 6FDA, possessed the best comprehensive thermally stable and soluble performance.