The present invention relates to a process for the preparation of an aqueous polymer solution containing at least one cationic or amphoteric (co)polymer, comprising the following steps: Hofmann degradation reaction on a (co)polymer based on at least one non-ionic monomer chosen from the group including acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile; post-processing of the resulting aqueous polymer solution of viscosity V1; characterized in that the post processing comprises the following successive steps: obtaining of an aqueous polymer solution containing at least one cationic or amphoteric (co)polymer derived from the Hofmann degradation reaction; post-processing of this aqueous polymer solution; characterized in that the post processing comprises the following successive steps: (a) adjustment of the pH of the aqueous polymer solution to a value greater than or equal to 5.5; (b) decrease of the pH of the aqueous polymer solution to a value between 2 and 5. The invention also concerns the use of this polymer solution as a flocculant, retention and/or drainage agent, and dry strength resistance in a paper manufacturing process.