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 .