Mixing apparatus and methods for the continuous production of monomer emulsions that may be used in the production of polymer dispersions by radical aqueous emulsion polymerization. The mixing apparatus can include a pipe-in-pipe injector (100) and a suitable rotor-stator mixer (102). Liquids are delivered to the rotor-stator mixer via an inner (110) and an outer (108) pipe in such a way as to substantially prevent feed inconsistencies in a feed ratio of the liquids prior to entering a mixing zone of the rotor-stator mixer for emulsion formation.