Synthesis and characterization of electrochromic poly(amide-imide)s bearing methoxy-substituted triphenylamine units

Highlights: → New poly(amide-imide)s with methoxy-substituted triphenylamine (TPA) units have been successfully synthesized. All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films with high thermal stability and good mechanical properties. The polymer films revealed good electrochemical and electrochromic stability. - Abstract: New poly(amide-imide)s (PAIs) 3a-d and 3'a-d with methoxy-substituted triphenylamine (TPA) units were prepared by the direct polycondensation from various imide ring-preformed dicarboxylic acids 2a-d with 4,4'-diamino-2'',4''-dimethoxytriphenylamine (1) and 4,4'-diamino-4''-methoxytriphenylamine (1'), respectively, using triphenyl phosphite and pyridine as condensing agents. For the comparative study, the referenced PAIs 3''a-d without methoxy substituents on the TPA unit were also prepared from 2a-d with 4,4'-diaminotriphenylamine (1''). All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films. The glass-transition temperatures (Tgs) of these PAIs ranged from 196 to 298 deg. C and the 10% weight-loss temperatures were in excess of 445 deg. C in nitrogen. Cyclic voltammograms of the PAI films cast onto the indium-tin oxide (ITO)-coated glass substrate exhibit one reversible oxidation redox couples at 0.73-0.89 V vs. Ag/AgCl in an electrolyte/acetonitrile solution. The polymer films revealed good electrochemical and electrochromic stability, with coloration change from a pale yellow neutral form to a green oxidized form. After over 100 redox cycles, the polymer films still exhibited good redox and electrochromic reversibility. The 3 and 3' series PAIs exhibited enhanced redox-stability and electrochromic performance as compared to the parent 3'' analogs without methoxy substituents on the TPA unit.