Synthesis and properties of novel electroactive poly(amic acid) and polyimidecopolymers bearing pendant oligoaniline groups

A series of novel electroactive copolymers of poly(amic acid) (PAA) bearing pendant aniline tetramer groups were prepared via direct polycondensation from novel electroactive diamine (EDA), 4,4'-diaminodiphenyl ether (p-ODA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA). The structures of the copolymers were confirmed by FT-IR and 1H NMR measurements. Then the prepared PAA copolymers were heated at 300 °C to induce cyclization, and transformed into polyimide (PI) films. The obtained PI films exhibited excellent thermal stability and outstanding mechanical properties. The PAA copolymers films had reversible redox couples with good cycle stability. The stepwise oxidation of as-prepared PAA copolymers by ammonium persulfate is monitored by UV-vis spectroscopy. The absorption peak at 571 nm underwent a red shift when it transformed from emeraldine state to pernigraniline state. Moreover, the PAA copolymers films revealed electrochromic behaviors with a color change from yellowish at its neutral state, to green, and finally to dark blue. They also exhibited extremely high optical contrast (%ΔT) up to 63% at 700 nm, moderate coloration efficiency (CE ≈ 100 cm2 C−1) and low switching times of 3.9 s at 0.8 V and 1.3 s for fast bleaching.