Dispersant for calcium sulphate-based compositions

A method comprising introducing a copolymer as a dispersant into a binder composition that includes at least one mineral binder, the binder composition being based on calcium sulfate, wherein

• the copolymer comprises a polymer backbone and side chains bonded thereto and there are at least one ionizable monomer unit M1 and at least one side chain-bearing monomer unit M2,
• the copolymer has a nonrandom distribution of the monomer units Ml and/or the monomer units M2 in a direction along the polymer backbone in that the copolymer has a gradient structure in at least one section AA in a direction along the polymer backbone with respect to the ionizable monomer unit M1 and/or with respect to the side chain-bearing monomer unit M2, and the copolymer, in addition to the at least one section AA having a gradient structure, has a further section AB, wherein there is essentially a constant local concentration of the monomers and/or a statistical or random distribution of the monomers over the entire section AB,
• a proportion of the calcium sulfate, based on all the mineral binder in the binder composition, is at least 30% by weight,
• a molar ratio of the monomer units Ml to the monomer units M2 in the copolymer is in the range of 0.5-6,
• the ionizable monomer unit M1 in the copolymer has a structure of the formula I
• the side chain-bearing monomer unit M2 includes a structure of the formula II
• where
• R1 forms a ring together with R4 to give —CO—O—CO—, or R1, in each case independently, is —COOM and/or —SO2-0M, and R4, in each case independently, is H, —COOM or an alkyl group having 1 to 5 carbon atoms;
• M, independently of one another, represents H+, an alkali metal ion, an alkaline earth metal ion, a di- or trivalent metal ion, an ammonium ion or an organic ammonium group;
• R2, R3, R5 and R6, in each case independently, are H or an alkyl group having 1 to 5 carbon atoms;
• R7, in each case independently, is H, —COOM or an alkyl group having 1 to 5 carbon atoms;
• m=0, 1 or 2;
• p=0 or 1;
• X, in each case independently, is —O— or —NH—;
• R8 is a group of the formula -[AO]n—Ra, where A=C2− to C4-alkylene, Ra is H, a Cl- to C20-alkyl group, -cycloalkyl group or -alkylaryl group;
• and
• n=2-250.