there is disclosed a process of preparing vinyl dispersion resins by conducting the polymerization reaction of the vinyl monomer or monomers in an aqueous medium in the presence of a polymerization initiator or catalyst and an emulsifier or emulsifier system to form a vinyl resin latex , which is then subjected to an ultrafiltration step by forcing the same through a semipermeable membrane leaving behind the polymer particles and reusing the permeate , which contains dissolved monomer and emulsifier , in the further production of vinyl resin latices . unexpectedly , further use of the permeate substantially reduces polymer buildup in the reactor and since the ultrafiltration step increases the polymer particle concentration in the latex , considerable heat energy is saved in the spray - drying step .