Polyoxymethylene, where a ratio of a low molecular weight component having a molecular weight of 10,000 or less in a molecular weight distribution is 7.0% or less of the total, and the molecular weight distribution is obtained by measurement by gel permeation chromatography (GPC) using polymethyl methacrylate (PMMA) as a standard substance.

The patent application relates to a process for preparing polyoxymethylene by polymerization of a reaction mixture (R.sub.G) which comprises at least one formaldehyde source and at least one initiator mixture (I.sub.G), wherein the initiator mixture (I.sub.G) comprises at least one polymerization initiator and at least one solvent of the general formula (I)
R.sup.1—O—[—R.sup.3—O—].sub.m—R.sup.2  (I), where m is 1, 2, 3 or 4; R.sup.1 and R.sup.2 are each, independently of one another, C.sub.3-C.sub.6-alkyl; R.sup.3 is C.sub.1-C.sub.5-alkylene.

The patent application relates to a process for preparing polyoxymethylene by polymerization of a reaction mixture (R.sub.G) which comprises at least one formaldehyde source and at least one initiator mixture (I.sub.G), wherein the initiator mixture (I.sub.G) comprises at least one polymerization initiator and at least one solvent of the general formula (I)
R.sup.1—O—[—R.sup.3—O—].sub.m—R.sup.2  (I), where m is 1, 2, 3 or 4; R.sup.1 and R.sup.2 are each, independently of one another, C.sub.3-C.sub.6-alkyl; R.sup.3 is C.sub.1-C.sub.5-alkylene.

It has been desired to develop a method for producing an oxymethylene polymer, by which an oxymethylene polymer having a high polymerization degree can be produced with high efficiency while suppressing increase in the amount of generation of an odor. Further, it has been desired to develop an oxymethylene polymer resin composition, wherein generation of an odor at the time of molding or after molded to obtain a molded body is suppressed. The present invention provides a method for producing an oxymethylene polymer, wherein the oxymethylene polymer is produced by polymerizing a cyclic oligomer of formaldehyde, and wherein a boron trifluoride compound and an aryl fluoride boron compound are used as polymerization catalysts. The present invention also provides an oxymethylene polymer resin composition containing an oxymethylene polymer and a derivative of an aryl fluoride boron compound.

It has been desired to develop a method for producing an oxymethylene polymer, by which an oxymethylene polymer having a high polymerization degree can be produced with high efficiency while suppressing increase in the amount of generation of an odor. Further, it has been desired to develop an oxymethylene polymer resin composition, wherein generation of an odor at the time of molding or after molded to obtain a molded body is suppressed. The present invention provides a method for producing an oxymethylene polymer, wherein the oxymethylene polymer is produced by polymerizing a cyclic oligomer of formaldehyde, and wherein a boron trifluoride compound and an aryl fluoride boron compound are used as polymerization catalysts. The present invention also provides an oxymethylene polymer resin composition containing an oxymethylene polymer and a derivative of an aryl fluoride boron compound.

A method for producing an oxymethylene copolymer, in which a copolymer starting material containing a trioxane and a comonomer is subjected to a polymerization reaction in the presence of a polymerization initiator that contains an acidic compound (A), and where: the copolymer starting material contains a basic compound (B); an acidic compound (C) that is different from the acidic compound (A) is added into the copolymer starting material before performing the polymerization reaction, thereby causing a reaction between the basic compound (B) and the acidic compound (C) in advance; and the polymerization reaction is carried out by means of melt polymerization.

A process for producing polyoxymethylene polymers comprises the reaction of aqueous formaldehyde solution with an aqueous solution of a base, wherein A) a starter solution comprising formaldehyde is initially charged and B) an aqueous formaldehyde solution and a base are added to the starter solution to obtain a reaction mixture. The starter solution in step A) has a temperature of ≥40° C. to ≤46° C. and the additions of the solutions in step B) are performed at a temperature of the reaction mixture of ≥40° C. to ≤46° C. The base is an alkali metal hydroxide and/or an alkaline earth metal hydroxide and the molar ratio of formaldehyde to base is ≥55:1 to ≤90:1 based on the total amounts of formaldehyde and base employed in the process. The base in step B) is added in aqueous solution.

A process for producing polyoxymethylene polymers comprises the reaction of aqueous formaldehyde solution with an aqueous solution of a base, wherein A) a starter solution comprising formaldehyde is initially charged and B) an aqueous formaldehyde solution and a base are added to the starter solution to obtain a reaction mixture. The starter solution in step A) has a temperature of ≥40° C. to ≤46° C. and the additions of the solutions in step B) are performed at a temperature of the reaction mixture of ≥40° C. to ≤46° C. The base is an alkali metal hydroxide and/or an alkaline earth metal hydroxide and the molar ratio of formaldehyde to base is ≥55:1 to ≤90:1 based on the total amounts of formaldehyde and base employed in the process. The base in step B) is added in aqueous solution.

A process for making an oxymethylene polymer comprising polymerizing at least one compound capable of forming —CH.sub.2O— repeat units (monomer) in the presence of at least one ester of the general formula I (ester): R.sup.1—CO—O—R.sup.2 (I) wherein R.sup.1 can be hydrogen, wherein R.sup.1 and R.sup.2 are independently of each other linear or branched C.sub.1 to C.sub.10 alkyl C.sub.5 to C.sub.7 cycloalkyl —[R.sup.3-0-].sub.nR.sup.4 wherein R.sup.3 is a linear or branched C.sub.2 to C.sub.5 alkylen and R.sup.4 is a linear of branched C.sub.1 to C.sub.5 alkyl and n is an integer of from 1 to 5. and in the presence of at least one Lewis acid.

A process for making an oxymethylene polymer comprising polymerizing at least one compound capable of forming —CH.sub.2O— repeat units (monomer) in the presence of at least one ester of the general formula I (ester): R.sup.1—CO—O—R.sup.2 (I) wherein R.sup.1 can be hydrogen, wherein R.sup.1 and R.sup.2 are independently of each other linear or branched C.sub.1 to C.sub.10 alkyl C.sub.5 to C.sub.7 cycloalkyl —[R.sup.3-0-].sub.nR.sup.4 wherein R.sup.3 is a linear or branched C.sub.2 to C.sub.5 alkylen and R.sup.4 is a linear of branched C.sub.1 to C.sub.5 alkyl and n is an integer of from 1 to 5. and in the presence of at least one Lewis acid.