Abstract: The present invention relates to a process for preparing a masterbatch rubber containing polymer bound functionalized moieties. The process comprises the emulsion polymerization at a temperature from 40.degree. C. to 100.degree. C. of (a) at least one functionalized monomer that contains a polymerizable vinyl group; with (b) at least one copolymerizable conjugated diene monomer selected from the group consisting of butadiene-1,3,2 chlorobutadiene-1,3, isoprene, piperylene and conjugated hexadienes, wherein the polymerization is conducted in the presence of from (1) from 2 to 30 parts by weight of an ionic surfactant per 100 parts by weight of organic components and (2) about 10 to about 70 parts by weight of a plasticizer based on 100 parts by weight of total monomers.