Synthesis of highly transparent and heat-resistant polyimides containing bulky pendant moieties

A new diamine with bulky pendant biphenyl and ortho -position dimethyl structures, 4,4′-((1,1′-biphenyl)-4-ylmethylene)bis(2,6-dimethylaniline), was synthesized via a one-pot reaction of 4-biphenyl carboxaldehyde and 2,6-dimethylaniline. The diamine was employed to polymerize with several dianhydrides via one-step condensation under high-temperature conditions. The light yellow or colorless polyimide (PI) films obtained were found to have cut-off wavelengths in the range 286–358 nm and transmittance over 80% in the visible region (400–780 nm). Meanwhile, these PIs possessed excellent solubility in common organic solvents, even in low-boiling-point solvents such as chloroform (CHCl 3 ), dichloromethane (CH 2 Cl 2 ) and tetrahydrofuran. The glass transition temperatures ( T g ) of the PIs were determined to exceed 343 °C, even to 456 °C. All PI films were flexible with a tensile strength of 78–119 MPa, a Young's modulus of 2.0–2.5 GPa and elongation at break of 4.0%–8.2%. Therefore, these colorless PIs can be used as candidate materials for flexible display substrates. © 2019 Society of Chemical Industry