SEPARATION PERFORMANCE OF DVB CROSS-LINKED POLYURETHANES

Polyurethanes (PUs) were prepared from hydroxyl-terminated polybutadie ne (HTPB) and 4,4'-dicyclohexylmethane diisocyanate (H12MDI) and 1,4-b utane diol (1,4-BD) by step growth polymerization. The crosslinkage be tween the HTPB soft segment of PUs was formed by adding divinyl benzen e (DVB) as crosslinking agent to the PU solution. The permeability and selectivity of an air or water/ethanol mixture of crosslinked PU memb ranes were investigated. The effect of hard segment content, DVB conte nt, feed concentration and feed temperature on the gas and liquid sepa ration were studied. The gas and liquid permeabilities of HTPB-based P U membranes with a suitable amount of crosslinking agent, which hinder ed the hard segment aggregation, were found to be higher than those of uncrosslinked ones. All the separation performances are explained by the flexibility of soft segments and aggregation of hard segments of P Us. The hydrogen bonding index (HBI) and frequency difference measured by FTIR, a measure of the phase segregation and the average strength of the interpolymer hydrogen bonds, were utilized to study the sorptio n phenomenon and permselectivity of the prepared membranes. The change of glass transition temperature was determined by DSC, which can be u sed to show the degree of crosslinking of these membranes. The results of the FTIR and DSC measurements exhibit the degree of crosslinking w ith different DVB content and hence the gas and liquid permselectiviti es as well. (C) 1998 Elsevier Science Ltd. All rights reserved.