Improving of the structures and properties of functional polyimide films by direct blend method

Triphenylamine (TPA)-based polyimides (PIs) have excellent discoloration characteristics and widely used as functional films. However, these PIs usually exhibit lower mechanical and thermal properties, and TPA units as the electron donor also weaken the optical transmittance of PIs. Utilized blending with diaminodiphenyl ether (ODA)-based PIs, we successfully prepared the blend polyimide (BPI) films containing ODA/TPA units, to realize complementary advantages of excellent mechanical, thermal, optical, and electrochemical properties. Among them, the tensile strength of BPI-53 film (mole ratio of TPA/ODA = 5:3) is reached up to 105.5 MPa, which is 641.9% much higher than 14.22 MPa of TPA-PI film. Moreover, the thermal stability of BPI-53 film is also significantly improved. T-5 (temperature of 5% weight loss) can be increased to 548.26 degrees C for BPI-53 film, and the weight residual rate at 800 degrees C in N-2 atmosphere is increased by an addition of 4%. Besides, BPI-53 film also has good transmittance property in district of 400-700 nm, and the variation range of transmittance under 1.0 V positive bias voltage is of 36.61%. For the electrochromics, the discoloration properties of blend polyamide acid (BPAA) dry film can be well maintained.