Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Patent
1996-07-10
1997-11-18
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
525398, 525405, 526 61, 528241, C08G 400, C08G 600
Patent
active
056888970
DESCRIPTION:
BRIEF SUMMARY
This application is a 371of PCT/JP95/00579 filed Mar. 28, 1995.
TECHNICAL FIELD
The present invention relates to a method for producing an oxymethylene copolymer having excellent heat stability. Particularly, the present invention relates to a method for producing an oxymethylene copolymer having excellent heat stability by volatilizing residual polymerization catalyst to decrease its amount in the oxymethylene copolymer. The residual polymerization catalyst is contained in crude oxymethylene copolymer obtained by copolymerizing trioxane and a cyclic ether and/or a cyclic formal.
BACKGROUND ART
A crude oxymethylene copolymer obtained by copolymerizing trioxane and a cyclic ether and/or a cyclic formal contains active polymerization catalyst. Therefore, after the polymerization catalyst is deactivated, terminal moieties of the oxymethylene copolymer are generally stabilized by using an extruder.
It is known to deactivate the polymerization catalyst in an aqueous solution comprising a basic substance. However, this method has as a drawback that a molecular weight of the oxymethylene copolymer decreases and the amount of unstable terminal moieties increases before terminal stabilization because water simultaneously causes decomposition of main chains of the oxymethylene copolymer during deactivation of the polymerization catalyst.
Another known deactivation method involves deactivating the polymerization catalyst by adding a basic substance to crude oxymethylene copolymer. This method is industrially preferable because the main chain of the oxymethylene copolymer does not decompose during deactivation of the polymerization catalyst and facilities can be simplified. As examples of this method, Japanese Patent Publication No. 51014/1983 discloses a method which comprises adding a tertiary phosphine compound as a deactivation agent to a crude oxymethylene copolymer and then feeding the oxymethylene copolymer to an extruder to stabilize terminal moieties. U.S. Pat. No. 4,751,272 discloses a method for deactivating the polymerization catalyst by adding a hindered amine compound to the oxymethylene copolymer after polymerization. However, in these methods, since deactivated polymerization catalyst remains in the oxymethylene copolymer, heat stability of the product deteriorates.
U.S. Pat. No. 5,344,911 discloses a method for deactivating a polymerization catalyst, which comprises conducting copolymerization by using 1.times.10.sup.-3 to 1.times.10.sup.-2 % by mol of a polymerization catalyst based on a total amount of monomers, and then cooling the resultant product to below 45.degree. C. within 30 seconds after copolymerization. However, in this method, the molecular weight of the oxymethylene copolymer decreases and the amount of unstable terminal moieties increases before terminal stabilization because water causes decomposition of main chains of the oxymethylene copolymer while the polymerization catalyst is deactivated by cooling.
DISCLOSURE OF THE INVENTION
The present inventors have made extensive and intensive studies to obtain an oxymethylene copolymer having high heat stability. As a result, they have found a method for producing an oxymethylene copolymer having high heat stability by decreasing the amount of residual polymerization catalyst contained in the oxymethylene copolymer.
That is, the present invention provides a method for producing an oxymethylene copolymer, which comprises:
copolymerizing trioxane and a cyclic ether and/or a cyclic formal in the presence of at least one polymerization catalyst selected from the group consisting of boron trifluoride, boron trifluoride hydrate, and a coordination compound of an organic compound having an oxygen or a sulphur atom with boron trifluoride to form an oxymethylene copolymer containing residual polymerization catalyst,
volatilizing the residual polymerization catalyst to decrease its amount in the oxymethylene copolymer, by heating the obtained oxymethylene copolymer in an atmosphere of inert gas at or below its melting point, and/or reducing
REFERENCES:
patent: 4458064 (1984-07-01), Chatterjee
patent: 4692290 (1987-09-01), Steele et al.
patent: 4751272 (1988-06-01), Okita et al.
patent: 5344911 (1994-09-01), Yamamoto et al.
Komatsu Sumio
Tanigawa Yukio
Tanimura Noritaka
Asahi Kasei Kogyo Kabushiki Kaisha
Foelak Morton
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