A closed loop continuous emulsion polymerization apparatus at least comprising a circulation pump, a reactor tube which connects the outlet of the circulation pump to its inlet, at least one feed for supplying raw materials, an outlet, and means for cooling the tube, characterized in that the reactor further comprises an additional tube for by-passing a pig around the circulation pump, a pig receiving station which is in parallel connection with the circulation pump or the reactor tube, and optionally means for directing a pig into the pig receiving station. The invention allows simple removal of the pig from the reactor, afforts great freedom in selecting the type of circulation pump and material and shape of the pig, and enables total control over the launching of the pig substantially independent of the reaction medium flow.