VAPOR AND GAS-PERMEABILITY OF POLYURETHANE MEMBRANES .1. STRUCTURE PROPERTY RELATIONSHIP

Polyurethane (PU) membranes were prepared by means of a prepolymer technique. The PU ingredients include polyester- and polyether-type polyols, 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol. The glass transition temperature (Tg), density and crystallinity of the PU membrane were determined in relation to such phenomena as permeability for oxygen, nitrogen and vapor. The degree of crystallinity was found to be the most reasonable variable instead of Tg or density to describe the behavior of permeation of gas or vapor in PU membranes incorporating various types and molecular weights of polyols and having different hard/soft segment distributions. The permeability for gas and vapor is consistently increased by decreasing the degree of crystallinity in PU membranes of all the various compositions. © 1990.