Synthesis, cross-linking and carbonization of co-polyimides containing internal acetylene units for gas separation

Youchang Xiao, Tai Shung Chung*, Huai Ming Guan, Michael D. Guiver

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


Cross-linkable polyimides containing internal acetylene units have been synthesized by random copolymerization of 6FDA dianhydride, 2,3,5,6-tetramethyl-1,4-phenylenediamine (Durene) and 4,4′-diaminodiphenylacetylene (p-intA) diamine as materials for gas separation. Compared with 6FDA-Durene polyimide, 6FDA-Durene/p-intA co-polyimide shows denser polymer chain packing, which is confirmed by wide-angle X-ray diffraction (WAXD). The thermally treated co-polyimides are insoluble in various solvents and show an increase in Tg, indicating the formation of network structures among the polymer chains. Differential scanning calorimetry (DSC) and FT-Raman suggest that cross-linking arises from Diels-Alder cycloaddition between the internally arranged acetylene units along the polymer main chain, resulting in extended conjugated aromatic structures. The thermally cross-linked membranes show enhanced resistance to CO2 plasticization up to around 5 × 106 Pa (700 psi). The rigidified membrane structure provides increased gas selectivity without severely compromising gas permeability. The gas separation performance of carbonized membranes is remarkably superior to those of neat and cross-linked copolyimides because of a large increase in rigidification in the polymer matrix. A Diels-Alder cycloaddition reaction produces a much more rigid and planar conjugated aromatic structure in the polymer chains and results in a higher degree of graphitization during carbonization, which is confirmed by XPS and WAXD. Carbon membranes derived from co-polyimides with more internal acetylene units show much better gas separation performance than those derived from polyimides without internal acetylene units.

Original languageEnglish (US)
Pages (from-to)254-264
Number of pages11
JournalJournal of Membrane Science
Issue number1-2
StatePublished - Sep 15 2007

Bibliographical note

Funding Information:
The authors would like to thank A*Star and NUS for funding this research with the grant numbers of R-279-000-164-305 and R-279-000-184-112, respectively. Special thanks are due to Ms. Pei Shi Tin and Ms. Mei Lin Chng for their useful assistance.


  • Carbonization
  • Co-polyimide
  • Cross-linking
  • Gas separation
  • Membranes

ASJC Scopus subject areas

  • Biochemistry
  • General Materials Science
  • Physical and Theoretical Chemistry
  • Filtration and Separation


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