Process for producing a surfactant free, low molecular weight copolymer, comprising the steps of: polymerizing a composition comprising (i) at least one ethylenically unsaturated monomer having acidic functionality and being present in an amount of 95 - 75 % by weight, based on the total amount of monomers in said composition, and (ii) at least one ethylenically unsaturated monomer having no acidic functionality and being present in an amount of 5 - 25 % by weight, based on the total amount of monomers in said composition, in only water as polymerization reaction medium in the presence of a redox system of a hydroperoxide and a hydroxylammonium salt as polymerization initiator at atmospheric pressure and at a temperature in the range of 80 °C to 100 °C without use of a surfactant, and subsequently, after polymerization, neutralizing the reaction mixture by means of an alkali, thereby obtaining a surfactant free copolymer with a K value molecular weight in the range of 10 to 100, preferably 20 to 60, more preferably, 25 to 40, wherein the K value molecular weight is determined as described in the description, wherein the ethylenically unsaturated monomer having acidic functionality is selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), or sodium vinylsulfonate, and the ethylenically unsaturated monomer having no acidic functionality is selected from butyl acrylate, methyl methacrylate, ethyl acrylate, 2-ethylhexyl acrylate or vinyl acetate. polymerizing a composition comprising (i) at least one ethylenically unsaturated monomer having acidic functionality and being present in an amount of 95 - 75 % by weight, based on the total amount of monomers in said composition, and (ii) at least one ethylenically unsaturated monomer having no acidic functionality and being present in an amount of 5 - 25 % by weight, based on the total amount of monomers in said composition, (i) at least one ethylenically unsaturated monomer having acidic functionality and being present in an amount of 95 - 75 % by weight, based on the total amount of monomers in said composition, and (ii) at least one ethylenically unsaturated monomer having no acidic functionality and being present in an amount of 5 - 25 % by weight, based on the total amount of monomers in said composition, in only water as polymerization reaction medium in the presence of a redox system of a hydroperoxide and a hydroxylammonium salt as polymerization initiator at atmospheric pressure and at a temperature in the range of 80 °C to 100 °C without use of a surfactant, and subsequently, after polymerization, neutralizing the reaction mixture by means of an alkali, thereby obtaining a surfactant free copolymer with a K value molecular weight in the range of 10 to 100, preferably 20 to 60, more preferably, 25 to 40, wherein the K value molecular weight is determined as described in the description, wherein the ethylenically unsaturated monomer having acidic functionality is selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), or sodium vinylsulfonate, and the ethylenically unsaturated monomer having no acidic functionality is selected from butyl acrylate, methyl methacrylate, ethyl acrylate, 2-ethylhexyl acrylate or vinyl acetate.