Triphenylamine-Based Porous Organic Polymers with High Porosity: their High Carbon-Dioxide Adsorption and Proton-Conductivity Emergence

Amorphous porous organic polymers (POPs) feature high specific surface area and chemical and thermal stability; therefore, they are applied in various fields. It is previously reported that chemical polymerization using iodine as an oxidant enables the synthesis of amorphous POPs without impurities. In this study, an iodine-based chemical polymerization method is employed to maximize the specific surface area of polytriphenylamine, a typical amorphous POP. Furthermore, 1,3,5-tris[4-(diphenylamino)phenyl]benzene, a monomer with three triphenylamine moieties connected by a benzene core, is used to increase the number of reaction points and construct a rigid structure. The resulting poly[1,3,5-tris[4-(diphenylamino)phenyl]benzene] (pTTPA) exhibited a high specific surface area. Using 200 equivalents of iodine resulted in a pTTPA with the largest Brunauer–Emmett–Teller (BET) specific surface area (2134.6 m² g⁻¹) among previously reported triphenylamine-based amorphous POPs, and demonstrated a high CO₂ adsorption capacity (3.31 mmol g⁻¹ at 25 °C). Furthermore, pTTPA exhibited significant water–vapor adsorption when the BET specific surface area reached 1500 m² g⁻¹, leading to the emergence of proton conductivity (e.g., 4.33 × 10⁻⁶ S cm⁻¹ at 95% RH and 90 °C). The findings demonstrate that iodine-based chemical polymerization enables the maximization of the porosity of amorphous POPs and the development of proton conductivity within them.