Copolymers include two monomer components, a) an olefinic unsaturated monocarboxylic acid comonomer or an ester or a salt thereof of an olefinic unsaturated sulfuric acid comonomer or a salt thereof, and b) an ether comonomer of the general formula (I) Components a) and b) are present in amounts of from 30 to 90 mol-% and from 70 to 10 mol-%, respectively, and comonomer component a) is selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, allylsulfonic acid, vinylsulfonic acid and a salt thereof or an alkyl or hydroxyalkyl ester. Compositions including a hydraulic binder such as cement, gypsum, lime and anhydrite and the copolymer are also disclosed. The copolymer can be used as superplasticizer or dispersant for non-hardened (wet) and a hydraulic binder containing compositions.