Modified poly(ether ether ketone) (PEEK) was synthesized to produce ultrafiltration (UF) and nanofiltration (NF) membranes. The prepared polymer is soluble in some polar aprotic solvents, such as n-methyl-2-pyrrolidone and tetrahydrofuran, making it possible to prepare membranes from them via the phase inversion process. By introducing these films to a non-solvent bath, tight UF to open NF membranes could be prepared that were stable in water, alcohols and other solvents such as hexane and acetonitrile. A range of membranes was prepared and their performance was evaluated by filtration experiments with rose Bengal in isopropanol, while their morphology was investigated by scanning electron microscopy. In addition to the influence of polymer properties, such as molecular weight and polydispersity, the role of the PEEK concentration in the casting solution on membrane performance and morphology was investigated. The membranes were also tuned towards NF performance by introducing volatile a co-solvent to the casting solution. This led to NF membranes showing 90% retention for the aforementioned testing solution. (c) 2013 Elsevier B.V. All rights reserved.