Method for obtaining an aqueous solution of water-soluble cationic polymers P1 wherein the halides content is lower than 10% by weight of the polymer, the viscosity at 25°C is lower than 200 cps, said viscosity being determined for an aqueous solution of polymers P1 concentrated at 50% by weight by means of an apparatus equipped with a 2° cone-plate module, comprising 2.3 mL of a solution of polymers P1 in a measuring cell controlled at 25°C and whereof the shear is 7.34 s -1, the viscosity being the average of 10 viscosity measurements performed every 20 seconds, and the cationic charge density is greater than or equal to 4 meq.g -1, characterized in that it comprises the following successive steps: a) adding, at a temperature comprised between 0°C and 120°C, of at least one compound of formula to an aqueous solution of at least one water soluble cationic polymer P2 wherein the halides content is greater than 10% by weight of the polymer, the viscosity at 25°C is lower than 200 centipoise, said viscosity being determined for an aqueous solution of polymers P2 concentrated to 50% by weight, and the cationic charge density being greater than or equal to 4 meq.g -1, the compound of formula being defined by the formula: R 1 -COO - Y 1 +, wherein: - R 1 represents a hydrogen atom or a saturated alkyl chain, either linear or branched, comprising from 1 to 8 carbon atoms, that may contain at least one nitrogen atom and/or oxygen atom, said chain may be substituted by 1 to 4 carboxylate functional groups of formula -COR; - Y 1 + represents an alkali metal cation, an ammonium ion of formula R 2 -NH 3 +, or a quaternary ammonium of formula R 3 -N + (R 4)(R 5)(R 6); - R represents an OH group or a group O - Y 2 +; - Y 2 + represents an alkali metal cation or an ammonium ion of formula R 2 -NH 3 +; - R 2 represents a hydrogen atom or a saturated alkyl chain, either linear or branched, comprising from 1 to 4 carbon atoms; and - R 3, R 4, R 5 and R 6 represent, independently of each other, a saturated alkyl chain, either linear or branched, comprising from 1 to 4 carbon atoms; in order to obtain a mixture; b) stirring of the mixture obtained in step a) for at least 5 minutes in order to obtain a stirred mixture; c) decreasing of the temperature of the stirred mixture obtained at the end of step b) at a temperature comprised between -10°C and 50°C in order to obtain a cooled mixture; and d) liquid/solid separation of the cooled mixture obtained at the end of step c) in order to obtain an aqueous solution of cationic polymers P1. a) adding, at a temperature comprised between 0°C and 120°C, of at least one compound of formula to an aqueous solution of at least one water soluble cationic polymer P2 wherein the halides content is greater than 10% by weight of the polymer, the viscosity at 25°C is lower than 200 centipoise, said viscosity being determined for an aqueous solution of polymers P2 concentrated to 50% by weight, and the cationic charge density being greater than or equal to 4 meq.g -1, the compound of formula being defined by the formula: R 1 -COO - Y 1 +, wherein: - R 1 represents a hydrogen atom or a saturated alkyl chain, either linear or branched, comprising from 1 to 8 carbon atoms, that may contain at least one nitrogen atom and/or oxygen atom, said chain may be substituted by 1 to 4 carboxylate functional groups of formula -COR; - Y 1 + represents an alkali metal cation, an ammonium ion of formula R 2 -NH 3 +, or a quaternary ammonium of formula R 3 -N + (R 4)(R 5)(R 6); - R represents an OH group or a group O - Y 2 +; - Y 2 + represents an alkali metal cation or an ammonium ion of formula R 2 -NH 3 +; - R 2 represents a hydrogen atom or a saturated alkyl chain, either linear or branched, comprising from 1 to 4 carbon atoms; and - R 3, R 4, R 5 and R 6 represent, independently of each other, a saturated alkyl chain, either linear or branched, comprising from 1 to 4 carbon atoms; in order to obtain a mixture; - R 1 represents a hydrogen atom or a saturated alkyl chain, either linear or branched, comprising from 1 to 8 carbon atoms, that may contain at least one nitrogen atom and/or oxygen atom, said chain may be substituted by 1 to 4 carboxylate functional groups of formula -COR; - Y 1 + represents an alkali metal cation, an ammonium ion of formula R 2 -NH 3 +, or a quaternary ammonium of formula R 3 -N + (R 4)(R 5)(R 6); - R represents an OH group or a group O - Y 2 +; - Y 2 + represents an alkali metal cation or an ammonium ion of formula R 2 -NH 3 +; - R 2 represents a hydrogen atom or a saturated alkyl chain, either linear or branched, comprising from 1 to 4 carbon atoms; and - R 3, R 4, R 5 and R 6 represent, independently of each other, a saturated alkyl chain, either linear or branched, comprising from 1 to 4 carbon atoms; b) stirring of the mixture obtained in step a) for at least 5 minutes in order to obtain a stirred mixture; c) decreasing of the temperature of the stirred mixture obtained at the end of step b) at a temperature comprised between -10°C and 50°C in order to obtain a cooled mixture; and d) liquid/solid separation of the cooled mixture obtained at the end of step c) in order to obtain an aqueous solution of cationic polymers P1.