Synthesis and Electrochromic Properties of Triphenylamine-Based Aromatic Poly(amide-imide)s

Three new amide-preformed triphenylamine-diamine monomers, namely 4,4′-bis(p-aminobenzamido)triphenylamine (4), 4,4′-bis(p-aminobenzamido)-4″-methoxytriphenylamine (MeO-4), and 4,4′-bis(p-aminobenzamido)-4″-tert-butyltriphenylamine (t-Bu-4), were synthesized and subsequently used to produce three series of electroactive aromatic poly(amide-imide)s (PAIs) via two-step polycondensation reactions with commercially available tetracarboxylic dianhydrides. Strong and flexible PAI films could be obtained by solution casting of the poly(amic acid) films followed by thermal imidization or direct solution casting from the organosoluble PAI samples. The PAIs had high glass-transition temperatures of 296–355 °C and showed no significant decomposition below 500 °C. The PAIs based on diamines MeO-4 and t-Bu-4 showed high electrochemical redox stability and strong color changes upon oxidation. For the PAIs derived from diamine 4, the TPA radical cation formed in situ during the electro-oxidative process could dimerize to a tetraphenylbenzidine structure, resulting in an additional oxidation state and color change. These PAIs exhibited increased solubility, lowered oxidation potentials, and enhanced redox stability compared to their polyimide analogs.