Effects of molecular structure on the permeability and permselectivity of aromatic polyimides

• Published in: Journal of applied polymer science Vol. 61; no. 5; pp. 741 - 748
• Main Authors: Li, Yuesheng, Wang, Xuqiang, Ding, Mengxian, Xu, Jiping
• Format: Journal Article
• Language: English
• Published: New York Wiley Subscription Services, Inc., A Wiley Company 01.08.1996; Wiley
• Subjects: Applied sciences; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Polymer industry, paints, wood; Technology of polymers; Polyimide; Gas permeability; Molecular structure; Aromatic polymer; Aromatic copolymer; Selective permeability; Membrane; Imide copolymer; Property structure relationship; Experimental study
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/(SICI)1097-4628(19960801)61:5<741::AID-APP4>3.0.CO;2-O

Permeability coefficients of H2, O2, and N2 were measured under 10 atm at the temperature from ambient temperature up to 150°C in a series of structurally different aromatic homo‐and copolyimides, which were prepared from 4,4′‐oxydianiline (ODA) or 4,4′‐methylene dianiline (MDA) with various aromatic dianhydrides. The study shows that the molecular structure of the polyimides strongly influences gas permeability and permselectivity. As a result, the permeability coefficients of the polyimide membranes for each gas vary by over two orders of magnitude. In general, among the polyimide membranes studied, the increase in permeability of polymers is accompanied by the decrease in permselectivity, and the MDA‐based polyimide membranes have higher permeability than ODA‐based ones. Among the polyimides prepared from bridged dianhydrides, the permeability coefficients to H2, O2, and N2 are progressively increased in the order BPDA <BTDA <ODPA ∼ TDPA <DSDA <SiDA <6FDA, while H2/N2 and O2/N2 permselectivity coefficients are progressively decreased in the same order. The copolyimide membranes, which were prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), bis(3,4‐dicarboxyphenyl)dimethylsilane dianhydride (SiDA), and ODA, have favorable gas separation properties and are useful for H2/N2 separation applications. © 1996 John Wiley & Sons, Inc.