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 led to three series of electroactive aromatic poly(amide-imide)s (PAIs) by the 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 oC and showed no significant decomposition before 500 oC. The PAIs based on diamines MeO-4 and t-Bu-4 showed a high electrochemical redox stability, accompanied by 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, which led to an additional oxidation state and color change. These PAIs exhibited increased solubility, lowered oxidation potentials, and enhanced redox stability as compared to their corresponding polyimide analogs.