The invention describes an emulsion polymer which can be obtained by polymerization of a mixture comprising a) from 5 to 99.9% by weight of one or more monomers having a solubility in water of <2% by weight at 20.degree. C. and selected from the group consisting of monofunctional (meth)acrylate monomers, styrene and vinyl esters; b) from 0 to 70% by weight of one or more monomers which can be copolymerized with the monomers a); c) from 0 to 20% by weight of one or more doubly or multiply vinylically unsaturated compounds; d) from 0 to 20% by weight of one or more polar monomers having a solubility in water of >2% by weight at 20.degree. C.; and e) 0.1-95% by weight of at least one activator,with the components a) to e) adding up to 100% by weight of the polymerizable constituents of the mixture, and is characterized in that e1) the activator is a compound of the Formula I, ##STR00001## where the radicals R.sup.1 to R.sup.7 and X have the meanings given in the description; and in that e2) the activator e) is incorporated via covalent bonds into the emulsion polymer. The emulsion polymer makes it possible to form core-shell polymers having a protected activator fixed to the polymer and can be used particularly advantageously for controlling the pot life of two-component or multicomponent systems, for example in adhesives, pourable resins, floor coatings, compositions for reactive pegs, dental compositions or sealing compositions.