Method for making monomers with two quarternary amino group and (co)polymers obtained from said monomers

A method of manufacturing a compound having formula (I):

• in which:
• R1 represents H or —CH3;
• R2 represents one of —CH3, —C2H5, —C3H7 and —C4H9;
• the two R3 are the same or different and each represents one of —CH3, —C2H5, —C3H7, —C4H9 and —CH2C6H5;
• and
• the two X⊖ are the same or different and each represents Cl⊖ or Br⊖,
• characterised in that at least one quaternising agent of formula (II):
• R3—X⊖ (II)
• in which R3 and X⊖ are as defined above, is introduced into a solution, in an organic solvent or in a mixture of organic solvents, of a compound having formula (III):
• in which R1 and R2 are as defined above, at a temperature of 35 to 80° C., then the reaction is allowed to continue at said temperature until compound (III) has disappeared completely or substantially completely, after which water is added and then an aqueous solution of compound (I) is separated and the water removed as necessary.