Rc. Ruaan et al., Microstructure of HTPB-based polyurethane membranes and explanation of their low O-2/N-2 selectivity, J APPL POLY, 82(6), 2001, pp. 1307-1314
Polyurethane (PU) membranes usually have high gas permeability but low sele
ctivity. It was supposed that an increase of the hard-segment content in PU
membranes would enhance the selectivity since the hard segment has a highe
r oxygen affinity and could reduce the chain mobility. However, an attempt
to increase the O-2/N-2 selectivity by increasing the hard-segment content
failed. It was found that increase of the hard-segment content did increase
the gas solubility but the solubility ratio of oxygen to nitrogen was not
increased. Increase of the hard-segment content also reduced the permeabili
ties of both oxygen and nitrogen, but no improvement of the O-2/N-2 diffusi
vity ratio was observed. The microstructure of polybutadiene-containing PU
was examined by DSC and FTIR measurements. It was found that hydrogen bondi
ng between hard segments was the cause of the failure of selectivity improv
ement. Avoiding the formation of hydrogen bonds between the hard segments i
s the key for a successful improvement of the O-2/N-2 selectivity of the PU
membranes. (C) 2001 John Wiley & Sons, Inc.