Dynamic membranes were prepared from poly(N-isopropylacrylamide-co-heptadecyl vinyl ketone) having a lower critical solution temperature in an aqueous solution and being a micelle-forming surfactant. The dependence of the critical concentration of the copolymer micellization an temperature was shown to have an extreme character with a minimum at the lower critical solution temperature of thr copolymer. The dynamic membranes are formed on both the hydrophilic (cellulose) and hydrophobic (polyacrylonitrile) supports. For the penetrants studied. it was found that the dynamic membrane formed on the hydrophobic support favors the rejection of a PEG(6000). while that formed on the hydrophilic support rejects more effectively albumin and sodium cellulose sulfoacetate. We failed to realize a completely reversible thermal control of transport properties of the dynamic membranes obtained, while it was readily accomplished for the membranes obtained by grafting N-isopropylamide onto a cellulose matrix.