Disclosed are membranes formed from self-assembling block copolymers, for example, a diblock copolymer of the formula (I): ##STR00001##
wherein R.sup.1-R.sup.4, n, and m are as described herein, which find use in preparing nanoporous membranes. Embodiments of the membranes contain the block copolymer that self-assembles into a cylindrical morphology. Also disclosed is a method of preparing such membrane which involves hybrid casting a polymer solution containing the block copolymer to obtain a thin film, followed by evaporation of some of the solvent from the thin film, and coagulating the resulting this film in a bath containing a nonsolvent or poor solvent for the block copolymer.