This contribution describes a methodology to convert commercially available, microporous membranes into ion-exchange membranes using primary anchoring polymer (mono)layers and graft polymerization from the surfaces of the membranes. Atom transfer radical polymerization (ATRP) was used to modify the membranes with pyridinium, exchange groups. Polymerization time was used as the independent variable to manipulate the amount of grafted poly(2-vinylpyridine) on the membrane surface. Results indicate that by changing polymerization time, it is possible to tune the ion-exchange capacity and the average pore size in rational ways. Equally important, membranes with initially broad pore-size distributions had narrower pore-size distributions following polymerization. A polymerization time of 24 h reduced the pore-diameter polydispersity (PDP) from 2.05 to 1.44. A polymerization time of 8 h resulted in a static ion-exchange capacity of 7.32 x 10(-2) mmol/g (7.32 x 10(-2) meq/g) of dry membrane. (c) 2005 Elsevier B.V. All rights reserved.