Effect of temperature and structure on the free volume and water vapor permeability in hydrophilic polyurethanes

Zhi Fen Wang, Bo Wang, Xue Mei Ding, Ming Zhang, Li Ming Liu, Ning Qi, Jinlian Hu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

63 Citations (Scopus)


A series of hydrophilic polyurethane films based on polyester polyols poly(butylene adipate) (PBA), poly(ethylene adipate) (PEA) and poly(hexamethylene adipate) (PHA) as soft segments, are characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and positron annihilation lifetime spectroscopy (PALS), respectively. The WAXD results indicate hydrophilic PUs have crystalline peaks except PEA-PU. The measurements of free-volume hole property have been carried out over a temperature range of 253-323 K. According to variation of ortho-positronium (o-Ps) annihilation parameters with temperature, we observed that mean free-volume size increased rapidly with vanishing of crystalline region. The permeability coefficients of water vapor measured indicated that water vapor permeability (WVP) increased with the temperature increased in all membranes over 288-313 K. In the polyester-based PUs, PBA-PU has the highest WVP attributed to the highest fractional free volume (fV). The effect of chemical structure on WVP and fVhas been discussed. Experimental results indicated that water vapor permeability may be controlled by not only free volume, but also hydrophilicity of polymer and crystalline region.
Original languageEnglish
Pages (from-to)355-361
Number of pages7
JournalJournal of Membrane Science
Issue number2
Publication statusPublished - 1 Oct 2004


  • Crystalline region
  • Free volume
  • Hydrophilic polyurethane
  • Hydrophilicity
  • Water vapor permeability

ASJC Scopus subject areas

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


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