Design, synthesis and characterization of novel fluorinated polyimide membranes with bulky pendant for gas transport

Abstract

Three novel fluorinated polyimides (PIs) were synthesized via one‐step solution polycondensation from a new diamine monomer, 4‐(3‐methoxy‐4‐(difluoromethoxy)phenyl)‐2,6‐bis(4‐aminophenyl)pyridine, and three commercially available aromatic dianhydrides. The solubility, thermal, optical, hydrophobic and gas transport properties of the obtained PIs were investigated. The results demonstrated that these polymers present good solubility in dimethylformamide, N‐methylpyrrolidone, dimethylsulfoxide, dimethylacrylamide, CHCl3, tetrahydrofuran and CH2Cl2 at room temperature or upon heating. Meanwhile, they displayed excellent thermal properties with glass transition temperature of 261–345 °C, weight loss temperatures at 10% of 518–523 °C as well as char yield of 60–62% at 800 °C in nitrogen atmosphere. Furthermore, the PI membranes have good hydrophobic properties with water contact angle value in the range 90.1–92.0°. Moreover, they show excellent optical properties, with cut‐off wavelength (λcut‐off) values of 368–381 nm and wavelength values at 80% transmittance (λ80%) of 421–462 nm. The pure gas permeabilities of He, CO2, O2 and N2 of the PI membranes were measured by the method of constant volume–variable pressure. The PI containing 4,4′‐(hexafluoroisopropyl)diphthalic anhydride moiety exhibits the largest molecular chain spacing and free volume, giving the best gas transport performance in this work. Molecular simulation results show that the introduction of fluorine‐containing structure and bulky pendant into polymer backbones is beneficial for gas transport. © 2023 Society of Industrial Chemistry.