Novel temperature-sensitive and pH-sensitive polyurethane membranes: preparation and characterization

The polyurethane (PU) membranes with temperature and pH double sensitivities for water permeation were designed and prepared from a two-step solution polymerization from the crystalline polycaprolactone diols (PCL), 4,4-diphenylmethane diisocyanate (MDI) and pH-sensitive 2,2-dimethylol propionic acid (DMPA), etc. The structure and properties of PU membranes were characterized by differential scanning calorimetry meter, contact angle tester, mechanical tester, porosity tests, water flux tests, water absorption tests, etc. Results showed that all PU membranes had a similar crystalline melting transition in their soft segments. With increasing DMPA content, or -COOH group content, the mechanical property of PU membranes was decreased, but the surface wettability and porosity of PU membranes were increased, which were expected to improve the water flux and water absorption of PU membranes. When the environment temperature was raised above the temperature of crystal-melting transition (T-m) of the soft segments, the water fluxes across these PU membranes changed markedly, showing the temperature sensitivity. When pH varied around the dissociation constant (pKa) of DMPA contained in PU(2), PU(3) and PU(4) macromolecules, their water fluxes and water absorption were also obviously changed, showing the pH sensitivity. (c) 2014 Curtin University of Technology and John Wiley & Sons, Ltd.