Influence of polyimide precursor synthesis route and ortho-position functional group on thermally rearranged (TR) polymer properties: Pure gas permeability and selectivity

• Published in: Journal of membrane science Vol. 463; pp. 73 - 81
• Main Authors: Sanders, David F., Guo, Ruilan, Smith, Zachary P., Stevens, Kevin A., Liu, Qiang, McGrath, James E., Paul, Donald R., Freeman, Benny D.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2014; Elsevier
• Subjects: 6FDA; Acetates; Applied sciences; Carbon dioxide; Chemistry; Colloidal state and disperse state; Conversion; Dianhydrides; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; General and physical chemistry; HAB; Membranes; Permeability; Polybenzoxazole; Polyimide resins; Polymer industry, paints, wood; Rings (mathematics); Selectivity; Technology of polymers; TR polymer; HAB; TR polymer; Polybenzoxazole; 6FDA; Polyimide; Polymeric membrane; Gas permeability; Synthesis; Polymer; Selectivity; Precursor; Functional group
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2014.03.032

Pure gas permeability coefficients of CH4, N2, O2, CO2, and H2 are reported for thermally rearranged (TR) polymers derived from polyimides based on 3,3′-dihydroxy-4,4′-diamino-biphenyl and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB-6FDA). These HAB-6FDA polymers were prepared with hydroxyl, acetate, propanoate, and pivalate groups in the ortho-position to the imide ring. Polymers with acetate ortho-position groups were synthesized via either thermal or chemical imidization. Pure gas permeability was approximately five times higher after rearrangement at 450°C in TR polymers from polyimides with acetate, propanoate, and pivalate ortho-position groups relative to TR polymers prepared from polyimides with hydroxyl ortho-position groups. In samples with non-hydroxyl ortho-position groups, those with larger ortho-position groups had higher gas permeability for TR conversions less than roughly 60%, but permeability increased to similar values as conversion exceeded 60%. In all samples, the CO2/CH4 selectivity also approached a similar value as TR conversion increased. Despite their higher permeability, fractional free volume was not significantly higher in TR polymers from polyimides bearing non-hydroxyl ortho-position groups than in samples with hydroxyl ortho-position groups. Therefore, average free volume alone cannot explain this behavior, suggesting that free volume distribution is likely affected by these groups. •Decouples effects of synthesis route and precursor pendant group on gas transport.•Compares the effect of several precursor pendant groups on TR polymer properties.•Examines permeability increases after rearrangement and FFV increases.