usually composed of a polyether or polyester soft segment and a
hard segment. The hard segments consist of urethane and urea
linkages with rigid and bulky units. The strong molecular interaction
of a polar urethane, urea groups and the rigid units makes the
hard segment act as filler or physically cross linked. Many
researchers have investigated segmented PU as a new material to
improve the permselectivity for gas separation. The purpose of
these studies is to find the relationship between the structure of
the PU and their separation properties [11–15].