Triphenylamine‐based polyimides with trimethyl substituents for gas separation membrane and electrochromic applications

Two series of polyimides I–II with methyl‐substituted triphenylamine units were prepared from the diamines, 4,4′‐diamino‐2″,4″,6″‐trimethyltriphenylamine (Me3TPA‐diamine; 1) and 4,4′‐diamino‐4″‐methyltriphenylamine (MeTPA‐diamine; 2), and two commercially available tetracarboxylic dianhydrides via a conventional two‐step chemical imidization. All the polymers were readily soluble in many polar solvents and showed useful levels of thermal stability associated with high glass transition temperatures (266–340 °C) and high char yields (higher than 49% at 800 °C in nitrogen). The polymer films showed reversible electrochemistry/electrochromism accompanied by a color change from neutral pale yellow to green oxidized form with good coloration efficiency, switching time, and stability. The CO2 permeability coefficients (PCO2) and permeability selectivity (PCO2/PCH4) for these polyimide membranes were in the range of 34.1–229.2 barrer and 21.3–28.9, respectively.