Synthesis and properties of transparent random and multi-block polyamide-imide films with high modulus and low CTE

Two new series of transparent polyamide-imides (PAIs) with high modulus and low coefficient of thermal expansion (CTE) were prepared by random or block copolymerization of 4,4'-biphthalic dianhydride (BPDA) and p-phthaloyl chloride (TPC) with 2,2'-bis(trifluoromethyl)benzidine (TFDB). These series of PAIs displayed low CTE of 16-42 ppm/K, good mechanical properties with high tensile modulus ranging from 4.9 to 6.6 GPa, tensile strengths of 112-170 MPa and elongations at break of 2.0-5.4%, as well as high transparency with transmittances at 500 nm (T-500nm) of 84-87%, which was greatly affected by the feed ratio of monomer BPDA & TPC, and the block length caused by block polymerization. The block copolymer PAI-3-B1 presented the best comprehensive performance with high transparency (T-500nm) of 87%, low CTE of 16 ppm/K and high tensile modulus of 6.1 GPa.

Automated summary

Two new series of transparent polyamide-imides with high modulus and low coefficient of thermal expansion were synthesized by copolymerizing BPDA, TPC, and TFDB. The block copolymer PAI-3-B1 showed the best performance with high transparency, low CTE, and high tensile modulus.