Abstract: A crude polyacetal polymer obtained by polymerization or copolymerization and having as a principal component thereof connected oxymethylene radicals in a main chain is treated in a non-soluble liquid medium at temperatures higher than 80.degree. C. but lower than the melting point of the polymer and at heterogeneous equilibrium, moving the crude polymer and the non-soluble medium in opposite directions relative to each other.

Abstract: A continuous polymerization method to obtain polymer production in the form of fine particles from a liquid polymerization medium; the reaction being conducted in a polymerization reactor wherein mixing is effected by the action of a plurality of elliptical paddles mounted on each of dual rotating shafts, characterised in that the dual shafts are rotated in reverse directions to each other, and the paddles being enclosed by walls of the reactor with the inside surface of the walls closely defining the surface generated by the rotation of the ends of both sets of paddles; and with the ends of major axes of the elliptical paddles on one rotating shaft periodically approaching the ends of minor axes of the corresponding elliptical paddles on the other rotating shaft to effect a mixing action as well as a longitudinal shearing action across a notional interface between the two shafts. The method is particularly useful for the polymerization of trioxane.