Abstract: In a process for producing a stabilized oxymethylene copolymer by heat-melting, at a temperature ranging between the melting point of the copolymer and a temperature 100.degree. C.

Abstract: A process for producing a polyacetal homopolymer or copolymer which comprises continuously feeding a liquid starting mixture containing molten trioxane and a catalyst and optionally a comonomer through a feed opening of a reactor, said reactor being a continuously stirring-type mixer having two stirring shafts having a plurality of plate-like paddles fixed thereto the cross-section of each of said paddles taken perpendicularly of the axial direction of the stirring shaft having a shape of a convex lens, an ellipse or a quasipolygon inscribing a phantom circle at each vertex, one of said paddles facing another paddle fixed to the other stirring shaft and said one paddle being positioned such that it rotates while the edges thereof keep a slight clearance from the inner surface of the barrel and the other paddle; polymerizing the starting mixture while moving it toward the discharge opening by the rotation of the paddles, the improvement wherein the profiles of the paddles are changed, or the arrangement of the

Abstract: In a process for producing an oxymethylene homopolymer or copolymer having improved stability which comprises polymerizing trioxane or a mixture of trioxane and a cyclic ether and/or a cyclic acetal in bulk in the presence of a catalyst which is at least one compound selected from the group consisting of boron trifluoride, boron trifluoride hydrate and coordination compounds of boron trifluoride with organic compounds containing an oxygen or sulfur atom, the improvement which comprises performing the bulk polymerization without destroying the bulk polymerization system, or which comprises adding a tertiary phosphine compound to the polymerization system to deactivate the catalyst, before the polymerization system formed by the bulk polymerization is destroyed.

Abstract: In a process for producing a stabilized oxymethylene copolymer which comprises heat-melting an oxymethylene copolymer having unstable, unblocked terminals obtained by the copolymerization of trioxane with a cyclic acetal and/or a cyclic ether to heat decompose it in the presence of available heat stabilizers; the improvement which comprises heating said oxymethylene copolymer having unblocked terminals in a mixer at a temperature between the melting point of said oxymethylene copolymer and a point 100.degree. C. higher than said melting point under a pressure of 0.

Abstract: In a method for mixing a trioxane, a polymerization catalyst and a comonomer for producing of oxymethylene copolymers by continuously copolymerizing trioxane with a cyclic ether or a cyclic acetal as a comonomer, the improved method comprises following steps:spouting a comonomer and a polymerization catalyst from nozzle openings which are set adjacent to each other,while washing both openings at the tip end of the nozzles with a flow of trioxane,whereby mixing said comonomer, said polymerization catalyst and said trioxane,and then feeding the mixture to a polymerization reactor to effect copolymerization.The raw materials are mixed together before they are fed to the polymerization reactor, and no clogging trouble at the tip end of the nozzle for feeding a polymerization catalyst occurs. Further the resulting copolymer has a much superior heat stability.

Abstract: An acetal resin composition comprising an admixture of 100 parts by weight of an acetal resin and 0.01 to 15 parts by weight of a petroleum resin, said petroleum resin being prepared by polymerizing a cracked petroleum fraction boiling between -15.degree. C. and 200.degree. C. and containing unsaturated hydrocarbons, and having a molecular weight in the range of 400 to 2500 and a second order transition temperature in the range of 35.degree. to 90.degree. C.

Abstract: A process for polymerizing trioxane made from an aqueous solution of methanol-containing formaldehyde by a conventional method or copolymerizing the trioxane with another monomer, characterized bycooling the trioxane to crystallize it,allowing the trioxane in a crystalline state to stand in an open system in an atmosphere of air or an inert gas to remove polyoxymethylene dimethoxide from the trioxane,melting the trioxane, andpolymerizing the trioxane or copolymerizing the trioxane and the another monomer.

Abstract: A process for continuously producing an oxymethylene polymer by continuously polymerizing a starting monomer containing at least 50 mole% of trioxane in bulk in the presence of a catalyst, which comprises feeding the starting monomer into a first-stage polymerization reactor having a self-cleaning action to perform a first-stage polymerization reaction until the conversion reaches 40 to 70%, withdrawing the reaction mixture as a powder from the outlet of the first-stage polymerization reactor, feeding the reaction mixture into a second-stage polymerization reactor having a stirring action to perform a second-stage polymerization reaction until the conversion reaches 95 to 100%, and then withdrawing the polymerization product as a powder from the outlet of the second-stage polymerization reactor.