Among these polymers, mention may be made more particularly of the following cationic polymers: ( 1 ) homopolymcrs or copolymers of acrylic or methacrylic esters or amides containing amine functions, comprising at. least one of the units of formulae A, B and C below: in which: R1 and R2, which are identical or different, each represent a hydrogen atom or an alkyl group having from 1 to 6 carbon at