Positive latex including a straight, branched, or cross-linked cationic polyelectrolyte from the polymerization, in molar %, of: a molar ratio ≧70% and ≦99% of monomer units from at least one cationic monomer b) a non-zero molar ratio <20% of monomer units from N-(2-hydroxyethyl)acrylamide c) a non-zero molar ratio ≦15% of monomer units from at least one monomer of formula (I): A-C(=0)-0-[(CH2—CH(RI)-0]n-R, where n is, independently, a number between 1 and 50, A is an unsaturated aliphatic radical including 2 to 6 carbon atoms, R1 is a hydrogen atom, a methyl radical, or an ethyl radical, and R is a straight or branched, saturated or unsaturated aliphatic radical including 8 to 30 carbon atoms d) optionally, a molar ratio >0% and ≦10% of monomer units from at least one neutral monomer other than the N-(2-hydroxyethyl)acrylamide, it being assumed that the molar ratio is strictly less than that of the monomer units from the N-(2-hydroxyethyl)acrylamide, and optionally, a molar ratio of monomer units from at least one neutral monomer other than the N-(2-hydroxyethyl)acrylamide and e) optionally, a molar ratio >0% and ≦1% of a diethylene or polyethylene cross-linking monomer.
