Abstract: In an essentially horizontal totally enclosed cylindrical wiped-wall polymer reactor having an essentially horizontal polymer flow, a pool of polymer in its lower portion, and driven wheels to create high surface area in the polymer to facilitate evaporation of volatiles from the polymer, the improvement comprising a freewheeling drag wheel driven by the driven wheels, with a wiping means mounted on the driven wheels and actuated by the drag wheel to wipe the entire internal circumference of the cylindrical reactor. The drag wheel generates a force to urge the wiping means outward against the internal circumference of the reactor. The force is generated by the drag of the pool of polymer on the drag wheel. This keeps the wall of the reactor wiped with a fresh film of polymer. The process and apparatus is particularly adaptable to driven wheels and drag wheels eccentrically mounted in the reactor.