Importance

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Abstract

Polymer dispersant of polycarboxylate type comprising at least one copolymer obtained from a monomer composition comprising, in moles: A) 40 to 95% of at least one unsaturated carboxylic monomer, B) 5 to 60% of at least one acrylic ester or methacrylic ester monomer comprising a polyether chain, C) 0 to 20% of at least one third monomer selected from: acrylic ester or methacrylic ester or acrylamide or acrylamide derivative or vinylaromatic monomer or its sulphonated derivative, the copolymer having a controlled molecular mass distribution and being able to be obtained by a process comprising the stages of: i) polymerization in aqueous solution at a temperature ranging from 70 to 95.degree. C. with an initiation and transfer system comprising: D) an oxidizing agent, E) a reducing agent selected from metabisulphite salts, and preferably from sodium metabisulphite or potassium metabisulphite, the monomers/reducing agent molar ratio not exceeding 50, ii) semi-continuous addition of the oxidizing agent and of the mixture of monomers over a time ranging from 1 to 4 hours, iii) introduction of the reducing agent, either as vessel heel, before the beginning of the addition of the oxidizing agent and of the monomers, or semi-continuously, mixed with the monomers, or semi-continuously, as a separate feed from the latter and from the oxidizing agent. The invention also relates to a specific preparation process and to uses as plasticizer in inorganic hydraulic binder compositions or as dispersing agent in pigment pastes or aqueous polymer dispersions.

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First Claim