Provided is a an amphiphilic diblock copolymer including from 40 to 60% by weight, relative to the weight of the copolymer, of a hydrophilic block including a unit derived from an n-butyl acrylate monomer and a derived from a hydroxyethyl methacrylate monomer. The copolymer also includes from 40 to 60% by weight, relative to the weight of the copolymer, of a hydrophobic block including at least one unit derived from a methyl methacrylate monomer. Also provided is a polymeric membrane that includes the block copolymer and a hydrophobic polymeric matrix. This membrane is useful for treating an effluent, for example, water.