A polymer dispersant used as a fluidifier and plasticizer for hydraulic binder compositions and a dispersant for pigment pastes or polymer dispersions prepared by a method giving improved control of molecular weight distribution

摘要

A polycarboxylate polymer dispersant obtained by a specified method from a monomer mixture comprising 40-95 mol.% unsaturated carboxylic units, 5-60 mol.% of (meth)acrylic ester monomer units containing a polyether chain and 0-20 mol.% of units of at least one third monomer which is a (meth)acrylic ester or acrylamide or an acrylamide derivative or a vinyl aromatic or its sulfonated derivative, especially styrene or it's sulfonated derivative. The distribution of mol.wts. of the polymer is controlled by a method comprising the steps of (1) polymerization in an aqueous solution at 70-95[deg]C with an initiator and chain transfer system comprising an oxidant agent, preferably potassium, ammonium or sodium persulfate and sodium or potassium metabisulfites as a reducing agent serving as the transfer agent, in the absence of any other transfer agent at a ratio by moles of monomers to reducing agent not exceeding 50; (2) semi-continuous addition of the oxidant and monomer mixture over 1-4 hours; (3) the introduction of the reducing agent either before the introduction of the oxidant and monomers or semi-continuously either together with or separately from them. Independent claims are included for (1) the method; (2) a composition comprising the claimed dispersant; (3) a composition of hydraulic binder or a paste or mineral particles or a pigment paste comprising the claimed dispersant; (4) hardened articles obtained from the claimed compositions.