Abstract: Undesirable deposition of polyoxymethylene onto the inner wall of a polymerization vessel and onto a stirrer, which deposition is observed in the slurry polymerization of formaldehyde carried out in an inert organic liquid medium in the presence of a polymerization catalyst, can be minimized by carrying out the slurry polymerization in the presence of at least one polyvalent metal salt selected from polyvalent metal salts of alkylsalicylic acids and polyvalent metal salts of dialkyl esters of sulfosuccinic acid. Optionally, a polyethylene glycol monoether may be used in addition to the polyvalent metal salt.

Abstract: A method of stabilizing oxymethylene copolymers which comprises heating an oxymethylene copolymer in a hydrocarbonaceous mixed medium consisting of about 50 - 92% by weight of a hydrocarbon having 5 - 7 carbon atoms, about 6 - 48% by weight of an alcohol and about 2 - 20% by weight of water based on the total amount of the medium, at a temperature of from about 100.degree. to about 170.degree. C. in the presence of a salt selected from the group consisting of the sodium and potassium salts of ethylenediaminetetraacetic acid under the conditions of a pH value of from about 4 to about 7.