Novel polyimide ionene: Synthesis and characterization of polyimides containing aromatic bipyridinium salt

A series of 4,4′-(1,4-phenylene)-bis(N-aminoaryl-2,6-diphenyl pyridinium perchlorate)s were synthesized by the reaction of 4,4′-(1,4-phenylene)-bis(2,6-diphenyl pyrylium) with aromatic diamines. They were used as monomers to react with various aromatic tetracarboxylic dianhydrides, to prepare polyimides via a two-stage procedure that included a ring-opening condensation in N,N-dimethylformamide (DMF) to give poly(amic acid)s, followed by thermal cyclodehydration to polyimides. The inherent viscosities of these poly(amic acid)s and polyimides were in a range of 1.03-0.07 dl g-1 (0.5% in DMF at 25 °C). All polyimides had good solubilities in several polar aprotic solvents, such as DMF, N,N-dimethylacetamide (DMAc), etc. Polyimides derived from 4,4′-oxydiphthalic anhydride could form transparent flexible and tough films. They had a tensile strength range of 42-80 MPa, and an elongation around 5%. The glass transition temperatures of all polyimides were between 181 and 206 °C (differential scanning calorimetry). Thermogravimetric analyses indicated that they were fairly stable up to 300 °C, and 5% weight loss temperatures were recorded in the range of 337-367 °C in nitrogen. These polyimides were semi-conductors with conductivities around 10-8 ohm-1 cm-1 and their conductivities could be further increased up to 10-7 ohm-1 cm-1 by I2-doping. These bipyridinium-based poly(amic acid)s and polyimides could reversibly develop colour by u.v. irradiation.