Method of producing water-soluble cationic copolymers

A method of preparing a high molecular, high molecular, water-soluble cationic copolymer comprising:

• reacting in an aqueous system at least one N-vinylamide monomer having the general formula:
• ##STR20## with at least one cationic quaternary amine monomer of the general formula:
• ##STR21## wherein Z represents --C(.dbd.O)O(CH.sub.2).sub.n N.sup..sym. R.sup.4 R.sup.5 R.sup.6 X.sup..crclbar., --C(.dbd.O)NH(CH.sub.2).sub.n N.sup..sym. R.sup.4 R.sup.5 R.sup.6 X.sup..crclbar. or ##STR22## or --CH.sub.2 N.sup..sym. (R.sup.4 R.sup.5)CH.sub.2 CH.dbd.CH.sub.2 X.sup..crclbar., or mixtures thereof and n is 1 to 5, R.sup.1, R.sup.2 and R.sup.3 are independently selected from the group consisting of H or C.sub.1 to C.sub.3 alkyl;
• R.sup.4, R.sup.5 and R.sup.6 are independently C.sub.1 to C.sub.3 alkyl;
• and X is a halide, hydroxyl or alkylsulfate anion in a molar ratio of N-vinylamide to quaternary amine of from 1:99 to 99:1, in the presence of a free radical polymerization initiator and from 10 to 1500 ppm of an alkali or alkaline earth metal salt of ethylenediamine tetracetic acid and a pH of from 5 to 8 to provide a polymeric product;
• treating the resultant polymeric product with from 0.05 to 3 mole of an acid or base per molar equivalent of N-vinylamide monomer used to provide the polymeric product;
• and
• recovering a N-vinylamide/vinylamine/cationic quaternary amine copolymer having the general formula:
• ##STR23## wherein R.sup.1, R.sup.2, R.sup.3 and Z are the same as defined above, and wherein x, y, and q represent molar percents of monomeric units in the copolymer and q is 1 to 99 mol %, the sum of x+y+q is 100 mol % and the molar ratio of x to y is from 0 to 10.