A process of emulsion polymerization comprising (a) adding a reactive mixture to a reaction vessel, said reactive mixture comprising water, one or more emulsifiers, one or more acrylate monomers, and a crosslinker having a free radical reactivity ratio of less than 1, (b) providing conditions in which said reactive mixture undergoes emulsion polymerization to form a crosslinked core having a glass transition temperature, Tg, of less than or equal to 10° C., or in the alternative, wherein the crosslinker is in an amount sufficient such that the crosslinked core has a swell ratio between 8 and 15 in THF and forming a polymer having an original ratio of units derived from the crosslinker to units derived from the acrylate monomer(s); and (c) feeding additional crosslinker during polymerization in an amount sufficient to maintain the original ratio of crosslinker to acrylate monomer(s) is provided. Further disclosed is an impact modifier composition and a polymer composition comprising an impact modifier.