Porous membranes were developed in a two step process using supercritical CO2 technology. Copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) were synthesized for the first time in supercritical carbon dioxide (scCO(2)), being identified by H-1 NMR and FT-IR. The influence of the feed monomer ratio on their morphology, average molecular weight and T-g was studied. These PMMA-co-PMAA copolymers were then used in the preparation of thin pH-responsive membranes by scCO(2)-assisted phase inversion method. The prepared films were characterized by scanning electron microscopy, mercury porosimetry. dynamical mechanical analysis, swelling and contact angle measurements. in order to study their morphology, pH-responsive character, hydrophilicity and viscoelastic properties by changing the monomer ratio composition of the copolymer from 5 to 50 wt% of MAA with respect to the total mass of monomers. PMMA-co-PMAA membranes were then tested for a potential application as protein filtration devices. Bovine serum albumin (BSA) was used as a model protein and permeation measurements were performed at three different pHs (4.5, 5.0 and 7.4). The PMMA-PMAA (90:10) membrane showed a good performance in terms of BSA amount filtrated, with distinct profiles at different pH, and consequently capable to assume an efficient role in protein filtration processes. (C) 2009 Elsevier B.V. All rights reserved.