The present disclosure relates to high molecular weight polystyrene-polydialkylsiloxane-polystyrene (“SDS”) triblock copolymer compositions and methods of separating one or more organic compounds from an aqueous solution using membranes derived from SDS triblock copolymers. The methods may be used to separate the one or more organic compounds from an aqueous solution produced in a fermentation process. In some embodiments, the one or more organic compounds include an alcohol, such as, for example, ethanol. In other embodiments, the one or more organic compounds include acetone. In other embodiments, the one or more organic compounds include acetone, ethanol, and n-butanol produced in an acetone-ethanol-n-butanol (ABE) fermentation process. In other embodiments, the one or more organic compounds include one or more byproducts produced in a fermentation process.