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 degrees C, 5% weight loss temperatures (T(5%)s) in nitrogen with 459-505 degrees 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-500(nm)) 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-78 presented the best combination of high T-g of 401 degrees C and high tensile modulus of 5.0 GPa, low CTE value of 24 ppm/K, and high transparency (T-500nm) of 87.2%.