Block copolymers are promising as materials for ultrafiltration membranes due to their ability to self-assemble into periodic, ordered structures on length scales of ~550 nm. Most efforts towards fabricating functional membranes from block copolymers have targeted equilibrium morphologies, which may results in a number of potential disadvantages, including a lack of porosity in the as made films, thick separation layers, or tedious transfer and post-functionalization steps. In this dissertation, nonequilibrium block copolymer structures are used in the fabrication of ultrafiltration membranes. A system containing the triblock terpolymer poly(isoprene-b-styrene-b-4vinyl pyridine) and the solvents 1,4-dioxane and tetrahydrofuran is studied in detail. Ultrafiltration membranes fabricated from this system using a combination of selfassembly and non-solvent induced phase separation are shown to have a thin, isoporous separation layer above an asymmetric substructure. The structure and performance of these membranes are characterized using techniques such as electron microscopy, permeability, and solute rejection. The formation mechanism of the nonequilibrium triblock terpolymer membranes is studied using small angle X-ray scattering and grazing incidence small-angle X-ray scattering techniques.