Disclosed are self-assembled structures formed from self-assembling block copolymers, for example, a diblock copolymer of the formula (I): wherein R1-R4, n, and m are as described herein, which find use in preparing nanoporous membranes. In an embodiment, the block copolymer self-assembles into a cylindrical morphology. Also disclosed is a method of preparing such membrane which involves spin coating a polymer solution containing the block copolymer to obtain a thin film, followed by solvent annealing of the film. Further disclosed is a method of preparing porous membranes from the self-assembled structures.