Synthesis, characterization, and pervaporation properties of segmented poly(urethane-urea)s

Poly(urethane-urea)s (PUUs) from 2,4-tolylene diisocyanate (2,4-TDI), poly( oxytetramethylene)diols (PTMO) or poly(butylene adipate)diol (PBA), and var ious diamines were synthesized and characterized by Fourier transform infra red spectroscopy, gel permeation chromatography, differential scanning calo rimetry, and density measurements. Transport properties of the dense PUU-ba sed membranes were investigated in the pervaporation of benzene-cyclohexane mixtures. It was shown that the pervaporation characteristics of the prepa red membranes depend on the structure and length of the PW segments. The PE A-based PUUs exhibit good pervaporation performance along with a very good durability in separation of the azeotropic benzene-cyclohexane mixture. The y are characterized by the flux value of 25.5 (kg mu m m(-2) h(-l)) and the separation factor of 5.8 at 25 degrees C, which is a reasonable compromise between the both transport parameters. The PTMO-based PUUs display high pe rmeation flux and low selectivity in separation of the benzene-rich mixture s. At the feed composition of 5% benzene in cyclohexane, their selectivity and flux are in the range of 3.2 to 11.7 and 0.4 to 40.3, respectively, dep ending on the length of the hard and soft segments. The chemical constituti on of the hard segments resulting from the chain extender used does not aff ect the selectivity of the PUU membranes.It enables, however, the permeabil ity of the membranes to be tailored. (C) 1999 John Wiley & Sons, Inc.