Multiblock copolymers with increasingly complex block sequences—for example, triblock terpolymers—offer unique opportunities to create nanostructured materials, but this potential has been hindered by a vast design space that complicates the exploration of structure–property relationships. Here, we report a versatile and scalable strategy to separate parent ABC and isomeric ACB triblock terpolymers into libraries of fractionated samples spanning a wide range of compositions. Using a combination of controlled polymerization and automated chromatography, the synthesis and separation of less than 10 ABC and ACB parent materials gave rise to over 100 purified triblock terpolymers. Separations follow systematic and predictable trends in volume fraction resulting from an adsorption-based mechanism where chains rich in non-polar blocks elute first followed by more polar derivatives, yielding fractions with improved purity in composition and molar-mass dispersity. As evidenced by small angle X-ray scattering (SAXS), fractionation significantly enhances long-range order compared to as-synthesized parent materials and allows for the definitive identification of various nanoscale morphologies. This user-friendly separation strategy significantly increases the availability of well-defined ABC triblock terpolymer libraries to the polymer community while also improving sample quality and accelerating discovery.