Transparent polyamide-imide films with high Tg and low coefficient of thermal expansion: Design and synthesis

Two series of optically transparent polyamide-imides (PAIs) were prepared by copolymerization of trimelletic acid chloride (TMAc), p -phthaloyl chloride (TPC), 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine (TFDB) and 4,4’-(9-fluorenylidene) diamine (FDA). These series of PAIs displayed high glass transition temperatures ( T g s) ranging from 340 to 441 °C, 5% weight loss temperatures ( T 5% s) in nitrogen with 459–505 °C, and low coefficient of thermal expansion (CTE) of 21–56 ppm/K, which greatly affected by the feed ratio of rigid TPC units and cardo diamine in the polymer main chain. The transmittances at 500 nm (T 500nm ) of the PAI films were found in the range of 70.0–87.7%, All polymers demonstrated good organosolubility and mechanical properties with tensile strengths of 77–146 MPa, tensile moduli of 2.9–5.8 GPa and elongations at break of 2.9–8.2%. PAI-7-8 presented the best combination of high T g of 401 °C and high tensile modulus of 5.0 GPa, low CTE value of 24 ppm/K, and high transparency (T 500nm ) of 87.2%.