Polyoxymethylene copolymer and composition thereof

A polyoxymethylene copolymer having a melting point not lower than 167° C. and not higher than 173° C.,

• wherein a low-molecular weight polyoxymethylene copolymer which is contained in the polyoxymethylene copolymer and is extractable with chloroform is not more than 5000 ppm,
• wherein the polyoxymethylene copolymer is what has been obtained through the heat treatment of unstable terminal groups comprised of the polyoxymethylene copolymer in the presence of at least one quaternary ammonium compound represented by the formula (1) below:
• [R1R2R3R4N+]nX−n (1)
• wherein:
• each of R1, R2, R3 and R4 independently represents an unsubstituted or substituted C1-C30 alkyl group, a C6-C20 aryl group, an aralkyl group wherein an unsubstituted or substituted C1-C30 alkyl group is substituted with at least one C6-C20 aryl group, or an alkylaryl group wherein a C6-C20 aryl group is substituted with at least one unsubstituted or substituted C1-C30 alkyl group, wherein said unsubstituted or substituted alkyl group being linear, branched or cyclic, and said substituted alkyl group having at least one substituent selected from the group consisting of a halogen atom, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group and an amide group, and wherein at least one hydrogen atom of each of said unsubstituted alkyl group, said aryl group, said aralkyl group and said alkylaryl group being optionally replaced by a halogen atom;
• n represents an integer of from 1 to 3;
• and
• X represents a hydroxyl group, or an acid residue of a C1-C20 carboxylic acid, a hydroacid excluding a hydrogen halide, an oxoacid, an inorganic thioacid or a C1-C20 organic thioacid.