Properties of HTPB based polyurethane membrane prepared by epoxidation method

Hydroxyl-terminated polybutadiene (HTPB) based polyurethane (PU) was synthesized by solution polymerization. The PU was then cast into membrane. The epoxidation of HTPB based PU membrane by an in situ generated peracid method is discussed. The chemical composition of the epoxidized PU membrane was studied by infrared spectroscopy. The absorption peak at 970cm^-1 for the C=C double bond decreased with epoxidation time whereas the absorption peak at 1183cm^-1 for oxirane group increased. The absorption peak at about 1700-1740cm^-1 for the C=O group and -OH group at about 3200-3700cm^-1 increased with epoxidation time that indicated the side reaction of epoxidation took place. The oxirane weight content was determined by titration method. The density, tensile strength, elongations, and decomposition temperature of the epoxidized PU membranes were measured. The molecular weight between crosslinking points PU membrane was calculated. Contact angle and protein absorption of fibrinogen and albumin experiments were also determined. It was found that the density and the tensile strength of epoxidized PU membrane increased with increasing epoxidation time whereas the molecular weight between crosslinking points, elongation and the amount of protein adsorption on the epoxidized PU membrane decreased. By using Kaelble's equation and the contact angle data, the surface tension of epoxidized PU membrane was determined. It was found that the surface tension of epoxidized PU membrane increased whereas the contact angle decreased with epoxidation time. The property changes reduced the permeability of gas through epoxidized PU membrane, but increased the gas selectivity between oxygen and nitrogen. The activation energies (E_p) for gas diffusing through various epoxidized PU membranes were obtained by the Arrhenius law; it is evident that E_p increased with the extent of epoxidation.