Synthesis and characterization of electrochromic poly(amide-imide)s based on the diimide-diacid from 4,4′-diamino-4″-methoxytriphenylamine and trimellitic anhydride

A dicarboxylic acid bearing two preformed imide rings, namely 4,4′-bis(trimellitimido)-4″-methoxytriphenylamine (3), was prepared by the condensation of 4,4′-diamino-4″-methoxytriphenylamine (2) and two molar equivalents of trimellitic anhydride (TMA). A new family of aromatic poly(amide-imide)s (PAIs) containing the electroactive triphenylamine (TPA) unit were prepared by the triphenyl phosphite activated polycondensation of the diimide-diacid 3 with various aromatic diamines. All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films. They displayed high glass-transition temperatures (269-313 °C) and good thermal stability, with 10% weight-loss temperatures in excess of 521 °C in nitrogen and char yields at 800 °C in nitrogen higher than 68%. Cyclic voltammograms of the PAI films cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited one reversible oxidation redox couple at 0.91-0.93 V vs. Ag/AgCl in acetonitrile solution. The polymer films revealed a good electrochemical and electrochromic stability, with a color change from colorless neutral form to blue oxidized form at applied potentials ranging from 0.0 to 1.2 V. The PAIs containing the TPA unit in both imide and amide segments showed multicolor electrochromism: pale yellow in the neutral state, green in the semi-oxidized state, and deep blue in the fully oxidized state.