New cationic polymers

A method, comprising:

• mixing a copolymer P with water comprising suspended colloidal matter and finely divided suspended matter, thereby coagulating and flocculating the colloidal matter and finely divided suspended matter in the water,
• said copolymer P comprising, in the form of polymerized units,
• a) at least one compound of the general formula I
• wherein R1 and R2 are independently H, C1, C2 or C3 alkyl,
• and
• b) at least one compound of the general formula II
• wherein R3 is H or C1, C2 or C3 alkyl,
• Y is
• R4 is an aliphatic or cycloaliphatic or aromatic group bearing a positive charge,
• R5 and R6 are independently C1 to C3 alkyl,
• X− is an anion,
• wherein the molar ratio of components a) to b) is 5:95 to 45:65.