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.

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 present invention provides a method for producing an oxymethylene copolymer which involves polymerizing trioxane and a comonomer cationically at a polymerization temperature of 135 C. to 300 C. in the presence of a protic acid salt having the molecular weight of 1000 or less, and at least one polymerization initiator selected from the group consisting of protic acids, protic acid anhydrides, and protic acid ester compounds having the molecular weight of 1000 or less.

The present invention provides a method for producing an oxymethylene copolymer which involves polymerizing trioxane and a comonomer cationically at a polymerization temperature of 135 C. to 300 C. in the presence of a protic acid salt having the molecular weight of 1000 or less, and at least one polymerization initiator selected from the group consisting of protic acids, protic acid anhydrides, and protic acid ester compounds having the molecular weight of 1000 or less.

A high-quality polyacetal produced by a process including supplying a raw material comprising trioxane, a comonomer capable of copolymerizing with trioxane and a non-volatile protonic acid to a reactor of a continuous stirring/mixing machine type; carrying out a polymerization reaction of the raw material to produce a reaction mixture; vaporizing an unreacted monomer to separate the unreacted monomer from the reaction mixture and supplying the unreacted monomer to the raw material supplying; collecting a polyacetal copolymer from the reaction mixture into a collection unit which is arranged downstream from a discharge port and is adjusted to have a gauge pressure of 0.2 kPa or more; and adding a basic compound to the collected polyacetal and then subjecting the resultant mixture to a melt-kneading treatment to deactivate the non-volatile protonic acid.

A process for producing a polyacetal copolymer, the process making catalyst deactivation easy and efficient. Trioxane as a major monomer is copolymerized with one or more comonomers that are a cyclic ether and/or cyclic formal having at least one carbon-carbon bond, using a nonvolatile protonic acid as a polymerization catalyst at 100 C. or lower until the conversion reaches 50% and thereafter at a polymerization environment temperature of 115 C. to 140 C. This process includes: a crushing step in which a dry-process crusher is used to obtain a crude polyacetal copolymer crushed to such a degree that when the crude copolymer is screened with a sieve having an opening size of 11.2 mm, 90 parts by weight or more thereof passes therethrough; and a deactivation step in which a basic compound (e) is added to the crude copolymer and the mixture is melt-kneaded to thereby deactivate the polymerization catalyst.

A process for producing a polyacetal copolymer, the process making catalyst deactivation easy and efficient. Trioxane as a major monomer is copolymerized with one or more comonomers that are a cyclic ether and/or cyclic formal having at least one carbon-carbon bond, using a nonvolatile protonic acid as a polymerization catalyst at 100 C. or lower until the conversion reaches 50% and thereafter at a polymerization environment temperature of 115 C. to 140 C. This process includes: a crushing step in which a dry-process crusher is used to obtain a crude polyacetal copolymer crushed to such a degree that when the crude copolymer is screened with a sieve having an opening size of 11.2 mm, 90 parts by weight or more thereof passes therethrough; and a deactivation step in which a basic compound (e) is added to the crude copolymer and the mixture is melt-kneaded to thereby deactivate the polymerization catalyst.

Poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof are used in molding materials comprising polyoxymethylene or a copolymer containing a majority of oxymethylene units, for improving the flexural toughness of moldings formed from the molding materials.

A high-quality polyacetal produced by a process including supplying a raw material comprising trioxane, a comonomer capable of copolymerizing with trioxane and a non-volatile protonic acid to a reactor of a continuous stirring/mixing machine type; carrying out a polymerization reaction of the raw material to produce a reaction mixture; vaporizing an unreacted monomer to separate the unreacted monomer from the reaction mixture and supplying the unreacted monomer to the raw material supplying; collecting a polyacetal copolymer from the reaction mixture into a collection unit which is arranged downstream from a discharge port and is adjusted to have a gauge pressure of 0.2 kPa or more; and adding a basic compound to the collected polyacetal and then subjecting the resultant mixture to a melt-kneading treatment to deactivate the non-volatile protonic acid.

A process for producing a polyacetal copolymer, the process making catalyst deactivation easy and efficient. Trioxane as a major monomer is copolymerized with one or more comonomers that are a cyclic ether and/or cyclic formal having at least one carbon-carbon bond, using a nonvolatile protonic acid as a polymerization catalyst at 100 C. or lower until the conversion reaches 50% and thereafter at a polymerization environment temperature of 115 C. to 140 C. This process includes: a crushing step in which a dry-process crusher is used to obtain a crude polyacetal copolymer crushed to such a degree that when the crude copolymer is screened with a sieve having an opening size of 11.2 mm, 90 parts by weight or more thereof passes therethrough; and a deactivation step in which a basic compound (e) is added to the crude copolymer and the mixture is melt-kneaded to thereby deactivate the polymerization catalyst.