Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1996-05-06
1998-04-21
Marquis, Melvyn I.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
528408, 528417, C08G 6391
Patent
active
057418667
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for producing an acetal copolymer. More particularly, the present invention is concerned with a method for producing an acetal copolymer, which comprises copolymerizing trioxane with a cyclic ether which is copolymerizable therewith, wherein the cyclic ether is one which is obtained by adding to a fresh cyclic ether containing a peroxide derived therefrom in an amount of 15 ppm by weight or less in terms of hydrogen peroxide at least one sterically hindered phenol in an amount of from 10 to 500 ppm by weight, based on the weight of the fresh cyclic ether. By the method of the present invention, an acetal copolymer having high thermal stability can be stably obtained.
BACKGROUND ART
Methods for producing acetal copolymers by copolymerizing formaldehyde or a cyclic oligomer thereof, such as trioxane or tetraoxane, with a cyclic ether copolymerizable therewith have conventionally been known, and widely used on a commercial scale. However, the acetal copolymers obtained by conventional methods have an unsatisfactory thermal stability.
A factor causing a lowering of the thermal stability of acetal copolymers consists in decomposition of the acetal copolymers by oxidation.
In the course of the production of an acetal copolymer, oxidative decomposition of the acetal copolymer is likely to occur during the polymerization reaction of monomers and post-treatments of the obtained copolymer, such as removal of unreacted monomers, washing and drying of the obtained acetal copolymer. Examined Japanese Patent Application Publication No. 3-63965 (corresponding to EP 0128739 A1) discloses a method for producing an acetal copolymer, in which, for the purpose of preventing a lowering of the polymerization yield, a sterically hindered phenol is added to a monomer prior to the initiation of the polymerization reaction, in order to suppress not only the decomposition position of the main chain of the acetal copolymer during the polymerization reaction but also the oxidative decomposition of the acetal copolymer during the post-treatments. However, the thermal stability of the acetal copolymer obtained by the above-mentioned method is still unsatisfactory.
SUMMARY OF THE INVENTION
In these situations, the present inventors have made extensive and intensive studies with a view toward finding a cause for the oxidative decomposition of the acetal copolymer, which decomposition gives rise to a lowering of the thermal stability of the acetal copolymer. As a result, it has unexpectedly been found that, a peroxide, which is derived from a cyclic ether (hereinafter, frequently referred to simply as "derived peroxide"), (the derived peroxide is thus caused to be present in the cyclic ether to be used as a comonomer for producing an acetal copolymer though it is in a relatively small amount) largely influences the oxidative decomposition of the acetal copolymer. The amount of derived peroxide present in the cyclic ether increases during the storing of the cyclic ether, and when a cyclic ether, the derived peroxide content of which has exceeded a certain critical level, is used as a comonomer for copolymerization with trioxane, the thermal stability of the resultant acetal copolymers becomes extremely low.
In the copolymerization reaction of trioxane with a cyclic ether, the trioxane as a main monomer, which is originally liquid, undergoes phase change (phase transition) to a solid through a viscous liquid by the addition of a cation-active catalyst, while the copolymerization reaction advances. The period from the addition of the catalyst to the solidification of the liquid monomer is called a "polymerization induction period". As a result of further studies of the present inventors, it has also been unexpectedly found that, when a cyclic ether containing a derived peroxide in an amount exceeding a certain critical level is used, the polymerization induction period becomes extremely long, so that a continuous operation of copolymerization for producing an acetal copolymer be
REFERENCES:
patent: 4758608 (1988-07-01), Collins et al.
Schenck, et al. "Mit Benzophenon Photosensibilisierte Autoxydation Von Sek.Alkoholen Und Athern. Darstellung Von .alpha.-Hydroperoxyden" Chem. Bar., 96: 509-513 (1963) No Translation.
Ikeda, et al. "Autoxidation of 2-Alkenyldioxolanes and 2-Alkenyl-1,3-Dioxanes" J. Org. Chem., 29: 286-288 (1964).
Seyfarth, et al. "Reaktionen Von 2-Halogenmethyl-1.3-Dioxolanen Mit Molekularem Sauerstoff, Auslosung Einer Neuartigen Umlagerung" Chem. Ber., 101: 623 (1968) No Translation.
Hermann, et al. "Uber Den Einflu.beta. Von Reglern Auf Die Polymerisation Des Trioxans" Macromol Chem., 90: 1, 6 (1966) No Translation.
Yahiro Shyuzi
Yamamoto Minoru
Asahi Kasei Kogo Kabushiki Kaisha
Marquis Melvyn I.
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