Abstract: A polyoxymethylene copolymer which is a polyoxymethylene copolymer obtained by copolymerizing trioxane and 8 to 20 mol, per 100 mol of the trioxane, of 1,3-dioxolane and which (i) has a crystallization time period of 10 to 2,000 seconds at 143° C., (ii) withstands 30 to 1,000 cycles of a bending durability test and (iii) has residence heat stability for 40 minutes or more, and a molded article formed of the copolymer. According to the present invention, there can be provided a polyoxymethylene copolymer excellent in bending durability and heat stability and excellent in moldability, and a molded article formed thereof.

Abstract: A polyoxymethylene copolymer which is a polyoxymethylene copolymer obtained by copolymerizing trioxane and 8 to 20 mol, per 100 mol of the trioxane, of 1,3-dioxolane and which (i) has a crystallization time period of 10 to 2,000 seconds at 143° C., (ii) withstands 30 to 1,000 cycles of a bending durability test and (iii) has residence heat stability for 40 minutes or more, and a molded article formed of the copolymer.

Abstract: A process for producing a polyphenylene ether, which comprises contacting, with an aqueous solution of a chelating agent, a polyphenylene ether solution and adding a water-soluble poor solvent for the polyphenylene ether to precipitate the polyphenylene ether; and recovering the thus precipitated polyphenylene ether. A mixture remaining after the recovery of the polyphenylene ether is brought into contact with water to extract the water-soluble poor solvent, and a water phase containing the thus extracted water-soluble poor solvent is recovered by separation. The water-soluble poor solvent is separated and removed from the water phase by distillation, and the whole or a part of the remaining water phase is recycled as water to be brought into contact with the mixture, the remaining water phase having a content of a high-boiling-point organic substance of 1 wt. % or less.

Abstract: A process for producing an oxymethylene copolymer by polymerizing trioxan and 1,3-dioxolan in the presence of a cationically active catalyst, wherein (1) 1,3-dioxolan is used in an amount of 0.01 to 2.9 mol % based on trioxan; and (2) the cationically active catalyst is used in an amount of 1×10−7 to 1.2×10−4 mol based on 1 mol of trioxan. The process of the present invention makes it possible to obtain at a high yield an oxymethylene copolymer which has almost as high mechanical strength and stiffness as an oxymethylene homopolymer while retaining the tenacity and heat stability of an oxymethylene copolymer.

Abstract: A process for producing a polyphenylene ether, which comprises contacting, with an aqueous solution of a chelating agent, a polyphenylene ether solution and adding a water-soluble poor solvent for the polyphenylene ether to precipitate the polyphenylene ether; and recovering the thus precipitated polyphenylene ether. A mixture remaining after the recovery of the polyphenylene ether is brought into contact with water to extract the water-soluble poor solvent, and a water phase containing the thus extracted water-soluble poor solvent is recovered by separation. The water-soluble poor solvent is separated and removed from the water phase by distillation, and the whole or a part of the remaining water phase is recycled as water to be brought into contact with the mixture, the remaining water phase having a content of a high-boiling-point organic substance of 1 wt. % or less.

Abstract: An acetal resin composition comprising:(A) 100 parts by weight of an acetal resin,(B) 0.01 to 5 parts by weight of a terminal-etherified polyalkylene glycol of the formula (I)R.sup.1 --O--(--R.sup.2 --O--).sub.m --R.sup.3wherein R.sup.1 is a hydrogen atom, an aliphatic hydrocarbon group having 1 to 7 carbon atoms, an aryl group or an aralkyl group, R.sup.2 is an alkylene group having 2 to 3 carbon atoms, R.sup.3 is an aliphatic hydrocarbon group having 1 to 7 carbon atoms, an aryl group or an aralkyl group, and m is a number of at least 20, and(C) 0.01 to 2 parts by weight of an ester from a polyhydric alcohol having 2 to 10 carbon atoms and a higher fatty acid having 22 to 32 carbon atoms. This acetal resin composition has highly improved mold releasability when injection-molded without any substantial impairment of mechanicla properties and thermal stability inherent to an acetal resin and gives precision molded articles having little molding strain.

Abstract: An improved method of stabilizing a polyoxymethylene copolymer, which comprises(1) heat-melting a crude copolymer of trioxane and a cyclic ether and/or a cyclic acetal to form a first stabilized copolymer having a decomposition ratio (D.sub.220.sup.60), determined when it is heated at 220.degree. C. for 60 minutes in vacuum, of up to 2% by weight, and then(2) bringing the first stabilized copolymer into contact with steam containing 0.01 to 5% by weight of a basic compound at a temperature of at least 100.degree. C. but not exceeding the melting point of the copolymer to form a second stabilized copolymer.

Abstract: A process for producing an oxymethylene copolymer by copolymerizing trioxane with at least one cyclic comonomer selected from the group consisting of cyclic ethers and cyclic formals, said process comprising(1) polymerizing trioxane alone or with a cyclic comonomer in the presence of a polymerization catalyst until the conversion of trioxane reaches 10 to 95%, and(2) thereafter adding a cyclic comonomer and a polymerization catalyst to the reaction system and continuing the polymerization.

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 method for recovering polyphenylene oxide having a high bulk density and a reduced content of fine particles from a solution of a polyphenylene oxide, which comprises adding a non-solvent composed of a lower alkyl alcohol and water to an aromatic solvent solution of a polyphenylene oxide substantially free from impurities to precipitate the polyphenylene oxide, the weight ratio of the aromatic solvent to the lower alkyl alcohol being from 1:1 to 1:2 and the weight ratio of the lower alkyl alcohol to water being from 1:0.005 to 1:0.1 in the precipitation system, and the addition of the non-solvent being controlled such that a liquid composition of the aromatic solvent, the lower alkyl alcohol and water forms a single phase; and recovering the precipitated polyphenylene oxide.