The fabrication of nanoporous thin-film membranes from block polym ers is proposed. A computational modeling effort is described, which optimizes the polymer block lengths in order to obtain therm odynamically favorable phase-separated morphologies. Synthetic rout es to access po ly(ethylene oxide) and p oly (methyl methacrylate)-based block polymers are outlined. These materials were then prepared using controlled free rad ical polymerization. The relative adv antages and disadvantages of numerous routes are discus sed. Characterization of di-and triblock polymers using nuclear m agnetic resonance spectroscopy and size-exclusion chromatograph revealed less than id eal re-initiation and cha in growth o f macroinitiators. Preliminary phase-behavior of these materials is reported from smallangle x-ray scattering and scanning electron microscopy. 4 ACKNOWLEDGMENTS Sandia National Labora tories is a multi-p rogram laboratory managed and opera ted by Sandia Corporation, a wholly owned subsidiary of Lockheed Mar tin Corporation, for the U.S. Department of Energy's Nationa l Nuclear Security Adm inistration under contract DE-AC04-94AL85000.