Acrylic acid (AA) vapour plasma treatment was used to modify the surface properties of polyurethane membranes (PU). The chemical changes produced after plasma treatment were measured mainly by X-ray photoelectron spectroscopy (XPS). AA plasma treatment increased in all the experimental conditions studied, the concentrations of carbonyl and ester groups at the PU surface compared with traditional oxygen plasma modification. The pervaporation (PV) results demonstrated that AA plasma treated PUs had much higher selectivity for the separation of methanol from methyl-t-butyl ether than untreated and O-2 treated PU membranes. This selectivity is maximum at 100 W and 1 min of AA plasma treatment time. HR-XPS spectra showed that a thin film with similar chemical properties to the poly(acrylic acid) was formed on top of the PU membrane after 5-10 W AA plasma treatments. AFM results of standard Si(100) substrates treated with AA revealed the formation of a similar to 220 nm film at 5 W. However, Si substrates treated at 100 W, led to sputtering of the substrate. PU membranes treated with AA plasma at powers higher than 10 W showed a high C=O content and a decrease in the COO contribution (C Is envelope). This paper illustrates the importance of selecting the right plasma parameters to improve the efficiency of the PV process. (c) 2007 Elsevier B.V. All rights reserved.