Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Patent
1981-08-12
1983-04-19
Phynes, Lucille M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
525398, 528249, 528250, C08G 208
Patent
active
043806201
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for preparing a polyoxymethylene having a desired molecular weight and exhibiting improved melt fluidity and processability. More particularly, it is directed to the preparation of a polyoxymethylene superior in melt fluidity and in processability by polymerizing formaldehyde in the presence of a polyhydric alcohol as a molecular weight regulator.
BACKGROUND ART
It is stated in the specification of British Pat. No. 796,862 that the molecular weight of formaldehyde polymer depends upon the amounts of traces of water, methanol, and formic acid present in the polymerization system. The specification of U.S. Pat. No. 3,017,389 also describes a process for polymerizing formaldehyde in the presence of an anionic initiator and of a chain transfer agent such as a monoester, monohydric alcohol, acid anhydride, amide, or imide. Among the chain transfer agents referred to in these patent specifications, while compounds having a so-called active hydrogen give adequate rates of chain transfer, compounds including monoesters, acid anhydrides, amides, and imides, which have no active hydrogen, possess the disadvantage of showing low rates of chain transfer, which results in unsatisfactory regulation of the molecular weight. Moreover, the use of any of these chain transfer agents including monohydric alcohols as well gives a polyoxymethylene of inadequate melt fluidity and processability. Thus, there is still great room for improvement in these techniques.
On the other hand, U.S. Pat. No. 3,436,375 discloses the polymerization of trioxane or formaldehyde using a cationic polymerization catalyst in the presence of a poly-hydric compound. In the polymerization by use of a cationic polymerization catalyst, there occurs a main chain scission reaction referred to as hydride shift reaction, causing a decrease in molecular weight of the polymer. Additionally, this type of main chain scission occurs significantly in the polymerization of formaldehyde, and it is therefore extremely difficult with a cationic polymerization catalyst to obtain a polyoxymethylene with a sufficiently high molecular weight.
Polyoxymethylenes are widely used as engineering thermoplastics and are usually shaped by using molding techniques such as injection and extrusion. Improvements of polyoxymethylenes in melt fluidity and in processability are expected to develop applications thereof to a great extent.
DISCLOSURE OF THE INVENTION
As a result of extensive studies on the method of regulating the molecular weight of polyoxymethylene, the present inventors found that a polyhydric alcohol having at least three alcoholic hydroxyl groups in the molecule functions as a good molecular weight regulator, and that the produced polymer is excellent in melt fluidity and in processability, and they have accomplished this invention.
The object of the invention is to provide a technique for regulating the molecular weight in the polymerization of formaldehyde and at the same time to provide polyoxymethylenes having excellent melt fluidity and processability.
This object can be attained by polymerizing formaldehyde in the presence of an anionic polymerization catalyst and in the presence of a polyhydric alcohol having at least three alcoholic hydroxyl groups in the molecule.
When formaldehyde is polymerized in the presence of such a polyhydric alcohol, chain transfer and chain branching take place, thereby affecting the molecular weight of the polymer being regulated. The branched polymer thus produced has improved melt fluidity, and as a result it exhibits good processability in extrusion or injection molding.
Branching of polyoxymethylene chains can take place only in the presence of a polyhydric alcohol having at least three alcoholic hydroxyl groups in the molecule because the use of any other alcohol having one or two alcoholic hydroxyl groups gives rise to chain transfer but not chain branching.
BEST MODE FOR CARRYING OUT THE INVENTION
Now the invention is described more precisely.
The polyhydric
REFERENCES:
patent: 3017389 (1962-01-01), Langsdorf et al.
patent: 3436375 (1969-04-01), McAndrew
patent: 3457228 (1969-07-01), Fischer et al.
patent: 3485799 (1969-12-01), Park
patent: 3631124 (1971-12-01), Burg et al.
M. Imoto et al., "Formaldehyde--Its Chemistry and Industry", (1965), pp. 65-87.
W. Fukuta et al., "Polymerization of Formaldehyde by Cationic or Anionic Catalyst", (1961), pp. 154-157.
S. J. Barker et al., "Polyacetals", pp. 11-23.
Hamada Minoru
Matsuzaki Kazuhiko
Sakurai Hisaya
Asahi Kasei Kogyo Kabushiki Kaisha
Phynes Lucille M.
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