Synthesis and Characterization of Novel Homopolyimides Containing Pyridine and Morpholine Groups for Gas Separation by Molecular Design and Simulation

A novel 4-(4-(1-morpholinyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (MPAP) diamine monomer was designed and synthesized by introducing non-coplanar morpholine groups and pyridine heterocyclic structures. By one-step homopolymerization of MPAP and different dianhydrides, three new polyimides (PIs) were synthesized. The obtained PIs are easily soluble in common organic solvents, such as NMP, DMAc, and CHCl 3 . Simultaneously, PIs have high thermal performance ( T g  = 277–377 °C) and excellent thermal stability ( T d,5% and T d,10% are 460–487 °C and 525–545 °C). They also have good optical transparency ( λ cutoff  = 380–394 nm, λ 80%  = 469–482 nm) and hydrophobicity ( θ  = 87–92º). The free volume and gas adsorption are simulated by Materials Studio 2019 software, and the simulation results match the gas separation performance obtained from experimental test. They show good gas separation performance as well, especially PI-3 for the CO 2 /N 2 (up to 23.26), O 2 /N 2 (up to 5.02) and He/N 2 (up to 59.78) separations, which is close to the 1991 Robeson upper bound.