Dispersion polymerization process for water-soluble polymer

PURPOSE: To obtain a water-soluble polymer useful as a flocculant or the like at good efficiency in good yields by polymerizing a water-soluble monomer under specified conditions in an aqueous reaction mixture containing a polyvalent anionic salt, etc. CONSTITUTION: A water-soluble monomer containing 5 mol.% or above cationic polymer of formula I (wherein R 1 is H or CH 3 ; R 2 and R 3 are each a 1 or 2C alkyl; A 1 is O or NH; B 1 is a 2-4C alkylene or the like; and X 1 - is a counter anion) is polymerized in an aqueous reaction mixture to obtain a water-soluble polymer. The aqueous reaction mixture contains a polyhydric anionic salt, at least one polymeric dispersant containing 20 wt.% or above cationic monomer of formula II (wherein R 4 ' is R 1 ; R 5 ' and R 6 ' are each R 2 ; R 7 ' is H or a 1 or 2C alkyl; A 2 ' is A 1 ; B 2 is B 1 ; and X 1 ' - is X 1 - ), optionally, a low-molecular-weight polyhydric alcohol, and, optionally, a preformed seed polymer. The water-soluble polymer formed during the polymerization is insoluble in the aqueous reaction mixture, and a portion of the monomer is fed into the aqueous reaction mixture after the polymerization reaction has been initiated, whereupon the viscosity peak during the production can become lower than the peak viscosity developed in an equivalent batch polymerization. COPYRIGHT: (C)1995,JPO