Colorless polyimide copolymers derived from isomeric biphenyltetracarboxylic dianhydrides and 2,2′-bis(trifluoromethyl) benzidine

Colorless polyimide (CPI) copolymers were synthesized by one-step or two-step methods, using 2,2 '-bis(trifluoromethyl)benzidine (TFMB), 2,2 ',3,3 '-biphenyltetracarboxylic dianhydride (3,3 '-BPDA), and 3,3 ',4,4 ' biphenyltetracarboxylic dianhydride (4,4 '-BPDA) as the monomers. These polymers exhibited a d-spacing value of 5.7-6.7 angstrom, and their d-spacing values increased while the intensity of pi-pi stacking interactions decreased with the increase of 3,3 '-BPDA/TFMB contents. The solubility of the copolymers were gradually enhanced as the increase of 3,3 '-BPDA/TFMB contents. Their coefficients of thermal expansion and glass transition temperatures increased with 3,3 '-BPDA/TFMB contents, ranging from 15 to 68 ppm K-1 and 300 to 359 degrees C, respectively. These polymers exhibited excellent optical transparency (.10 < 390 nm, T450 > 83.2%, and b* < 4). CPI-4 and CPI-5 with 40 mol% and 20 mol% of 3,3 '-BPDA/TFMB contents exhibited well-balanced solution processability and physical properties. The CPI copolymers can be potentially used in optical and optoelectronic fields owing to their desirable overall properties.

Automated summary

Colorless polyimide (CPI) copolymers were synthesized using two-step or one-step methods with different monomers. The copolymers showed increased d-spacing values and decreased intensity of pi-pi stacking interactions with increasing 3,3'-BPDA/TFMB contents. Additionally, the solubility, thermal expansion coefficients, and glass transition temperatures of the copolymers were enhanced with higher 3,3'-BPDA/TFMB contents. These CPI copolymers exhibited excellent optical transparency and solution processability, making them suitable for optical and optoelectronic applications.