As membrane reactors are mostly applied at high temperatures, organic polymers are generally out of focus for preparing the catalytic membranes. The much milder conditions encountered in fine chemical synthesis justify their use in this area. As a dense polymer, they can actively interfere in the reaction by modulating sorption:and diffusion of reagents and products, leading to significantly enhanced catalytic activities. Both heterogeneous and homogeneous catalysts can be occluded. For the latter, these membranes additionally provide an easy way of dispersing and immobilising. (C) 2000 Elsevier Science B.V. All rights reserved.