Synthesis of hypercrosslinked microparticles is described and the effect of reaction conditions on adsorbent properties is discussed. Heterogeneous membranes based on hypercrosslinked microparticle adsorbent with a poly(phenylene oxide) binder were prepared and tested for separation of hydrogen from a isobutane/hydrogen mixture. The separation process was characterized by parameters, such as diffusion flux, permeability, and selectivity. The prepared membranes were superior to the homogeneous ones in permeability and to zeolite-filled membranes in selectivity. Selectivity reached values of about 540 in H-2/isobutane separation. (c) 2005 Elsevier B.V. All rights reserved.