a continuous throughput endless loop reactor for polymerizing monomers formed by a material conveying conduit connected in an endless loop having spaced apart raw material inlet means and polymer output means in which the output volume can be controlled by a pressure sensitive element and in which a coolant line passes internally through the conduit preferably becoming near the output means . reaction speed as well as thermal control is augmented by helical vanes of alternately pitch sections joining the coolant line and the interior walls of the conduit .