Synthesis, characterization, and gas separation properties of novel fluorinated co-polyimides with bulky side groups

Abstract

A series of random 6FDA-MFPAP/BAMF co-polyimides with different MFPAP:BAMF molar ratios (2:1, 1:1, 1:2, and 1:3) were synthesized from a novel diamine, 4-(3-methoxy-4-(difluoromethoxy)-phenyl)-2,6-bis(4-aminophenyl)pyridine (MFPAP); a commercial fluorene diamine (BAMF); and a dianhydride, 4,4'-(hexafluoroiso-propyl)diphthalic anhydride (6FDA). The prepared co-polyimides exhibited outstanding thermal performances ( T g > 345 °C, T d > 509 °C), good optical properties (λ cut-off > 342 nm, λ 80% > 410 nm), and hydrophobic properties (contact angle >91.8°). They also showed excellent solubility in both high and low boiling point organic solvents. The pure gas (He, CO 2 , O 2, and N 2 ) permeability of the co-polyimide membranes was measured using the constant volume-variable pressure method. The gas permeabilities of the membranes were superior to those of the commercial Kapton, Matrimid and P84, where the He permeability coefficient of 6FDA-MFPAP/BAMF (2:1) was 55.39 barrer. This can be reasonably explained and supported by the fractional free volume and molecular chain spacing of the polyimides. In addition, the gas transport performances of the copolymers have significantly improved over their corresponding homopolymers (6FDA-MFPAP and 6FDA-BAMF). And the 6FDA-MFPAP/BAMF co-polyimides with 2:1 and 1:1 M ratios of MFPAP/BAMF had the best gas separation performance for the gas pairs He/CO 2 and O 2 /N 2 , respectively, which was close to the Robeson upper limit in 1991. A series of containing bulky side group novel fluorinated co-polyimides with outstanding thermal performances, excellent solubilities, good optical properties, and hydrophobic properties were synthesized based on a novel diamine MFPAP, fluorene diamine BAMF and dianhydride 6FDA, they exhibit good gas separation properties and show the potential of application in gas separation field. • A series of novel fluorinated co-polyimides with bulky were designed and synthesized. • Polymers exhibited excellent soluble, thermal, optical and hydrophobic properties. • Diamine MFPAP effectively modulate the FFV and gas transport performance of PIs. • Gas transport performance of MFPAP/BAMF (1:1) and (2:1) PIs are closest to the 1991 upper bond.