Issue 9, 2021

The spirobichroman-based polyimides with different side groups: from structure–property relationships to chain packing and gas transport performance

Abstract

Spirobichroman-based polymers with high gas permeability and selectivity are promising for their applications as membranes in gas separation. In this study, three spirobichroman-based polyimides (PIs; 6FDA-FH, 6FDA-DH, and 6FDA-MH) were synthesised by the polyreaction between diamines containing different substituents (benzene ring, pyridine ring, and methyl group) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The physical properties, gas transport behaviour, d-spacing, dihedral angle of molecules, and fractional free volume of the PIs were investigated through experiments and molecular simulations. The PIs exhibited excellent thermal stability and good solubility in common organic solvents. The gas permeability of the PIs was investigated; the results highlighted the critical role of the substituents in the enhancement of the gas separation performance of polymer membranes. Detailed analysis of the PIs showed that 6FDA-FH exhibits the highest gas permeability. This can be ascribed to the loose packing of the polymer chain owing to the increased dihedral angle between the two planes. However, the methyl substituent in 6FDA-MH disrupts the polymer chain packing rather than changing the dihedral angle between the two planes, thus enhancing the gas permeability of 6FDA-MH. Furthermore, 6FDA-DH exhibited the highest CO2/CH4 selectivity, which is attributed to the CO2 affinity of the polymer containing the pyridine unit.

Graphical abstract: The spirobichroman-based polyimides with different side groups: from structure–property relationships to chain packing and gas transport performance

Supplementary files

Article information

Article type
Paper
Submitted
30 nov 2020
Accepted
19 jan 2021
First published
27 jan 2021
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2021,11, 5086-5095

The spirobichroman-based polyimides with different side groups: from structure–property relationships to chain packing and gas transport performance

S. Wang, X. Tong, C. Wang, X. Han, S. Jin, D. Wang, J. Yao and C. Chen, RSC Adv., 2021, 11, 5086 DOI: 10.1039/D0RA10113C

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