High water reduction powder preparation for dry mortar

A process for the production of a powdered copolymer P, said process comprising the steps of

• i) preparing an aqueous copolymer solution comprising 30-99 w %, based on the total weight of said aqueous solution, of a PCE-type copolymer comprising
• a) a molar parts of a structural unit S1 of formula I
• b) b molar parts of a structural unit S2 of formula II
• c) c molar parts of a structural unit S3 of formula III
• and d) d molar parts of a structural unit S4 of formula IV
• wherein
• each M independently from each other 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,
• each Ru independently from each other represents hydrogen or a methyl group,
• each Rv independently from each other represents hydrogen or COOM,
• m is 0, 1, 2 or 3,
• p is 0 or 1,
• each R1 and each R2 independently from each other represents
• C1- to C20-alkyl,
• -cycloalkyl,
• -alkylaryl or
• for -[AO]n—R4, where
• A represents a C2- to C4-alkylene,
• R4 represents H, C1- to C20-alkyl, -cyclohexyl or -alkylaryl, and
• n is an integer in the range of from 2-350,
• each R3 independently of the others represents NH2, —NR5R6, —OR7NR8R9,
• wherein R5 and R6 independently from each other stand for
• C1- to C20-alkyl, -cycloalkyl
• alkylaryl or -aryl,
• or for a hydroxyalkyl- or acetoxyethyl-(CH3—CO—O—CH2—CH2—) or
• hydroxyisopropyl-(HO—CH(CH3)—CH2—) or acetoxyisopropyl group (CH3—CO—O—CH(CH3)—CH2—);
• or R5 and R6 together form a ring of which the nitrogen is part, to form a morpholine or imidazoline ring,
• R7 is a C2-C4-alkylene group,
• each R8 and R9 independently from each other represent C1- to C20-alkyl,
• -cycloalkyl, -alkylaryl,
• -aryl or a hydroxyalkyl group,
• and a, b, c and d stand for the molar parts of the structural units S1, S2, S3 and S4, with a/b/c/d having values in the following ranges:
• (0.1-0.9)/(0.1-0.9)/(0-0.8)/(0-0.8), with the provision that a+b+c+d is equal to 1,
• ii) adding a base to adjust the pH of the aqueous copolymer solution to at least 10,
• iii) adding 0.01 to 5 w %, based on the weight of the aqueous copolymer solution, of at least one additive selected from anti-caking agents and/or anti-oxidants,
• iv) spray-drying the aqueous copolymer solution to obtain a powder, and
• v) optionally sieving.