Colorless polyimides from 2,2′,3,3′-biphenyltetracarboxylic dianhydride and fluorinated diamines

• High-molecular-weight CPIs were prepared using 3,3′-BPDA and fluorinated diamines. • 3,3′-BPDA-derived CPIs showed high d -spacing values due to the twisted structures. • 3,3′-BPDA-derived CPIs were highly soluble in common organic solvents. • 3,3′-BPDA-derived CPIs exhibited high T g of 287–414 °C and good thermal stability. • 3,3′-BPDA-derived CPIs showed λ 0 of <370 nm, T 450 of 80–89%, and YI of 1.4–13.4. In this work, 2,2′,3,3′-biphenyltetracarboxylic dianhydride (3,3′-BPDA) was exploited to produce colorless polyimides (CPIs), and their properties were systematically investigated. High-temperature polycondensation of 3,3′-BPDA with fluorinated diamines enabled the synthesis of CPIs with high molecular weights. The resulting CPIs displayed deficient chain packing owing to the steric hindrance and suppressed formation of charge transfer complexes (CTC), as confirmed by the interchain distances (5.9–6.7 Å). These CPIs were highly soluble in common organic solvents due to the enlarged interchain distances. Depending on the chain rigidity, the glass transition temperatures of the CPIs ranged from 287 to 414 °C. More importantly, these CPIs exhibited outstanding optical properties, with a cut-off wavelength of 355–370 nm, transmittance at 450 nm of 79.6–89.2%, and yellow index of 1.4–13.4.