A series of soluble aromatic poly(amide-imide)s (PAIs) was prepared from a new diamide–diamine monomer having biphenyl units with two CF3 groups. The diamide–diamine monomer was polymerized with 2,2′-bis(trifluoromethyl)benzidine and pyromelltic dianhydride through an imidization reaction to prepare PAIs with a controlled imide/amide bond ratio in the main chains. While the PAIs with the highest imide bond content showed a limited solubility, other PAIs were soluble in polar organic solvents and can be solution-cast into flexible freestanding films. All PAIs exhibited high thermal stability with 5% weight loss temperature (Td5) from 464 to 497 °C in air, and no appearance of glass transition up to 400 °C. Notably, the linear coefficient of thermal expansion (CTE) value of the PAI films was linearly decreased with the imide bond content and varied from 44.8 to 7.8 ppm/°C
