Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Patent
1992-06-02
1994-02-22
Kight, III, John
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
528232, 528233, 528239, 528242, 528244, 528485, 528489, 524155, 524157, 524158, 524284, 524401, 524745, 524779, 524786, C08G 1402
Patent
active
052888401
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a polyoxymethylene copolymer. In more particular, the invention relates to a polyoxymethylene copolymer having a specified terminal group composition and excellent in stability and mechanical properties.
BACKGROUND ART
Polyoxymethylenes synthesized by prior art techniques are classified broadly into homopolymers and copolymers. Polyoxymethylene homopolymers and polyoxymethylene copolymers of the prior art respectively have only one of the two desirable characteristics, namely either excellent mechanical property or excellent stability. That is, polyoxymethylene homopolymers obtained by homopolymerization of formaldehyde or trioxane are excellent in mechanical properties but are not satisfactory in stability; on the other hand, polyoxymethylene copolymers obtained by copolymerization of formaldehyde or trioxane with a cyclic ether or cyclic formal are excellent in stability but are poor in mechanical properties. With respect to long term resistance to heat or resistance to hot water, furthermore, even polyoxymethylene copolymers are not satisfactory.
Polyoxymethylene copolymers are usually obtained by copolymerizing formaldehyde or trioxane with a cyclic ether. U.S. Pat. No. 3,027,352 describes a copolymer obtained by cationically copolymerizing trioxane with ethylene oxide or 1,4-dioxolane.
Further, U.S. Pat. No. 3,337,503 discloses the use of methylal as a molecular weight controlling agent in the polymerization of trioxane. When methylal is used as the molecular weight controlling agent, the terminal group of the resulting polymer becomes the methoxy group.
In the polymerization of formaldehyde or trioxane or the copolymerization thereof with a comonomer using cationic catalyst, hydride shift (i.e., hydrogen abstraction) takes place, which results in scission of the main chain of the polymer and makes it impossible to obtain a high molecular weight polymer. Moreover, it is known that the terminals formed by the scission become the methoxy group and the formate group.
Further, when compounds having hydroxyl groups, such as water, methanol, formic acid, etc., are present in polymerization, they function as a chain transfer agent and form unstable terminal structures. A usually adopted remedial method is to decompose these unstable structures and stabilize the terminal groups as hydroxyethoxy groups, by application of post-treatment after polymerization. In the case of formic acid, however, terminal formate groups are formed simultaneously.
As described above, in the previous polyoxymethylene copolymers, terminal formate groups are formed during polymerization by chain transfer reaction caused by formic acid, which is an impurity in trioxane, and by hydride shift reaction, which is a side reaction caused by cationic catalyst, so that it has been difficult to reduce terminal formate groups.
The present invention relates to a polyoxymethylene copolymer which has both excellent stability and excellent mechanical property. In more particular, the invention relates to a polyoxymethylene copolymer which is excellent in stability and mechanical property and further in long term resistance to heat and resistance to hot water, and to the process for producing the same.
DISCLOSURE OF THE INVENTION
The present inventors have made extensive study on the stability of polyoxymethylene. As the result, they have found that by restricting to a certain range the amount of inserted oxyalkylene units in polyoxymethylene copolymer and the amount of terminal formate groups in the copolymer, a polyoxymethylene copolymer can be obtained which has highly excellent stability and mechanical property and excellent long term resistance to heat and resistance to hot water. The present invention has been accomplished on the basis of above finding.
Thus, the present invention relates to a polyoxymethylene copolymer having a molecular weight of 10,000-200,000 which comprises oxymethylene units (--CH.sub.2 O) and oxyalkylene units ##STR1## wherein R and R.sub.0 may be the same or diffe
REFERENCES:
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Chemical Abstracts, vol. 104, No. 26, Jun. 30, 1986, p. 16.
Chemical Abstracts, vol. 89, No. 4, Jul. 24, 1978, p. 19.
Matsuzaki Kazuhiko
Morishita Hirohisa
Acquah S. A.
Asahi Kasei Kabushiki Kaisha
Kight III John
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