To obtain a colloidal dispersion mixture having a specific rheological characteristics and enabling the production of mechanically stabilized copolymer dispersion systems by copolymerizing a water-soluble monomer with a water- insoluble comonomer in the presence of a specific emulsifying agent.

This colloidal dispersion mixture is obtained by copolymerizing (A) a water-soluble monomer with (B) a water-insoluble comonomer in the presence of (C) a micelle-forming emulsifying agent. The component A is preferably N-methyl-N-vinylacetamide, N-vinyl-2-pyrrolidone, N-vinylformamide or the like. The component B is preferably an (α-substituted) acrylate ester, a maleate ester or the like. The component C is preferably a nonionic emulsifying agent, a mixture of an ionic emulsifying agent with a nonionic emulsifying agent, or the like. The copolymerization is preferably carried out as a free radical-addition polymerization.