Gas permeation and mechanical properties of thermally rearranged (TR) copolyimides

Qiang Liu, Donald R. Paul, Benny D. Freeman

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60 Citations (Scopus)


Gas transport and mechanical properties are reported for a series of copolyimides and their corresponding thermally rearranged (TR) analogs. Random copolyimides of APAF/HAB-6FDA with various compositions were synthesized via chemical imidization from 2,2′-bis (3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF), 3,3′-dihydroxy-4,4′-diaminobiphenyl (HAB), and 2,2′-bis-(3,4-dicarboxy-phenyl) hexafluoropropane dianhydride (6FDA). These copolyimides were thermally treated at temperatures between 350 °C and 450 °C to prepare TR polybenzoxazoles (PBOs). Pure gas permeabilities of H2, CH4, N2, O2, and CO2 were measured at 35 °C with upstream pressures ranging from 3 to 17 atm. In general, gas permeability increased and selectivity decreased as TR conversion increased. Gas permeability also increased with increasing APAF content in the polyimides as a result of higher fractional free volume (FFV) imparted by the extra hexafluoroisopropylidene group in APAF. Stress-strain relationships were recorded for the polyimides and their TR analogs. As polyimides underwent thermal rearrangement, samples became more rigid, and tensile stress and elongation at break decreased. A similar trend in mechanical properties was also observed as APAF content increased, which was attributed to the lower molecular weight of APAF-containing polymers, resulting from the lower reactivity of APAF relative to that of HAB.

Original languageEnglish
Pages (from-to)378-391
Number of pages14
Publication statusPublished - 15 Jan 2016
Externally publishedYes


  • 6FDA
  • APAF
  • HAB
  • Mechanical property
  • Polybenzoxazole
  • Thermally rearranged

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