Process for producing inverse microemulsions of cationic copolymers

A process for producing inverse microemulsions of a cationic copolymer of a nonionic monomer and a cationic monomer of high molecular weight, comprising the following steps:

• a) preparing an aqueous phase, by mixing together:
• a.1) water;
• a.2) a mixture of the monomers to be copolymerized comprising, at least, one nonionic monomer and one cationic monomer, at a total monomer concentration between 20% and 45% by weight with regard to the total weight of the microemulsion, and at a nonionic monomer to cationic monomer ratio between 99:1 and 20:80 by weight;
• a.3) optionally, a metal chelating agent;
• and
• a.4) optionally, a polymerization initiator;
• b) separately preparing an oily or organic phase, by mixing together:
• b.1) an organic solvent;
• and
• b.2) a surfactant system whose HLB is between 8,8 and 9,5, comprising at least two nonionic surfactants, (i) at least a nonionic surfactant “A” which has an HLB between 3 and 8 and has at least one hydrophobic chain with at least one unsaturation and number of carbon atoms equal to or greater than 18, and (ii) at least a nonionic surfactant “B” which has an HLB higher than 12 and one or more C8-18 saturated hydrophobic chains;
• c) degasifying said aqueous and oily phases, together or separately, with an inert gas until the oxygen concentration therein is lower than 0.5 ppm;
• d) mixing said aqueous and oily phases in an inert atmosphere in case they have been degasified separately;
• and
• e) polymerizing said aqueous and oily phase mixture in an inert atmosphere.