Method for manufacturing paper and cardboard

A method for producing a sheet of paper or cardboard from a fibrous suspension, comprising:

• a) injecting a polymer P2 into a fibrous suspension,
• b) forming of a sheet of paper or cardboard,
• c) drying of the sheet of paper or cardboard,
• wherein the polymer P2 is prepared, before said a), from a water-soluble polymer P1 in an inverse emulsion form, the water-soluble polymer P1 is a water-soluble polymer of at least one nonionic monomer selected from the group consisting of acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile,
• wherein the polymer P2 is obtained by a reaction Re comprising adding the water-soluble polymer P1 in the inverse emulsion form to an aqueous solution M1 comprising (i) an alkali metal hydroxide, or an alkaline earth metal hydroxide, or mixtures thereof and (ii) an alkali metal hypohalide, or an alkaline earth metal hypohalide, or mixtures thereof,
• the reaction Re has a reaction time of 10 seconds to 5 hours after the addition of the water-soluble polymer P1 in the inverse emulsion form.