Synthesis of Soluble and Highly Transparent Homopolyimides for Gas Separation by Molecular Design and Simulation

A novel diamine monomer, 4-(4-(2,6-bis(4-(4-aminophenoxy)phenyl)pyridyl)phenyl)morpholine (AOPPM), featuring non-coplanar morpholine groups, oxyether linkages, and pyridine heterocycles, was successfully designed and synthesized. A series of polyimides were obtained via one-step homopolycondensation of AOPPM with four different dianhydrides. The resulting mopPIs exhibited good solubility in common organic solvents, including NMP, DMAc, CH 2 Cl 2 , and CHCl 3 . Meanwhile, the mopPIs demonstrated high thermal performance ( T g = 232°C–328°C) and excellent thermal stability ( T 5% = 419°C–464°C and T 10% = 460°C–520°C). They also exhibited good optical transparency ( λ cutoff = 352–393 nm, λ 80% = 414–478 nm) and moderate hydrophobicity ( θ = 82°–88°). The fractional free volume and gas adsorption properties were simulated using Materials Studio 2019, and the simulated results were consistent with the experimentally observed gas separation performance. The mopPI-1 membrane also exhibited excellent gas separation performance, particularly for CO 2 /N 2 (up to 10.33), O 2 /N 2 (up to 2.48), and He/N 2 (up to 20.62) gas pairs, approaching the 1991 Robeson upper bound. Graphical A new diamine monomer containing ether bonds, morpholine groups and pyridine heterocycles was synthesized by molecular design, and four new morpholinyl polyimides were prepared from it. The polyimides exhibit good solubility, hydrophobicity, thermal properties, mechanical properties, excellent optical transparency, and efficient gas separation performance. The reliability of the experimental data was further confirmed through molecular dynamics simulation, including free volume and gas adsorption simulation.