Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-12-22
2001-07-03
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S616000, C568S685000
Reexamination Certificate
active
06255536
ABSTRACT:
FIELD
The present invention relates to perfluorinated vinyl ethers and to the preparation thereof. These monomers are valuable comonomers for fluoroelastomers with enhanced low temperature properties.
BACKGROUND
The benefits of modifying fluoropolymers by vinyl ethers are described in various review articles. See, for example, Modern Fluoropolymers, John Scheirs, Wiley Series in Polymer Science 1997 and in other literature (e.g. Emel 'yanov et al, Zh. Org. Khim (1994) 30(8) 1266-70; Krespan, Carl G., DuPont de Nemours U.S. Pat. No. 4,273,728).
Partly fluorinated vinyl ethers and their copolymers are described in A. E. Feiring et al, DuPont de Nemours U.S. Pat. No. 5,326,917. Long chain vinyl ethers provide in fluoroelastomers excellent low temperature properties (see Uschold et al, U.S. Pat. No. 4,513,128).
The preparation of perfluoro(alkyl vinyl ethers) by fluorination with elemental fluorine is known. See Hung et al, U.S. Pat. No. 5,350,497. This patent discloses the fluorination of selected partially fluorinated (di)chloroethyl ethers (followed by dehalogenation to the corresponding perfluoro(alkyl vinyl ether).
Perfluorinated long chain perfluoroethers are difficult to prepare, especially those vinyl ethers without branching and more than 3 atoms in the alkyl group. For example, perfluorovinyl ethers are commonly prepared by two routes. See, for example, Modern Fluoropolymers, J. Scheirs, Wiley 1997 pp 376-378.
Addition of perfluorinated acid fluorides to hexafluoropropylene oxide results in an acid fluoride that may be converted to a salt and pyrolyzed to give the described perfluorovinyl ether. The oligomerization of hexafluoropropylene oxide with itself and conversion to a salt and subsequent pyrolysis gives long chain but branched ethers.
A more recent process prepares perfluorovinyl ethers by using perfluoro alkyl hypofluorites and dichlorodifluoroethylene followed by dehalogenation using, for example, Zn.
As noted, it is difficult to provide long chain perfluorinated ethers, especially vinyl ethers, when using these processes. A difficulty in the dichloro process includes the hazards of making and handling the R
2
f
—OF species. Because of these hazards, this species also has a limited availability. An improved process for making perfluorinated vinyl ethers is needed, particularly for making linear perfluorinated vinyl ethers.
SUMMARY
The present invention describes a process for the preparation of a perfluorinated vinyl ether of the formula CF
2
═CF—O—R
f
wherein R
f
is a linear, branched or cyclic perfluorinated aliphatic group that may contain oxygen atoms thereby forming additional ether linkages. R
f
groups containing such oxygen atoms are referred to as perfluoroalkyleneoxy groups. R
f
preferably contains from 1-20, more preferably from 1 to 10, carbon atoms in the backbone. R
f
may also contain sites of terminal unsaturation.
Preferably, the perfluorinated ethers prepared according to the invention are selected from perfluorinated linear vinyl ethers of the formula CF
2
═CF—O—R
f
. In one embodiment, the vinyl ethers are preferably free of chlorine atoms.
The process of the invention comprises the steps of:
(a) providing a hydrocarbon precursor comprising at least one 2-alkoxypropionate moiety, derivative, or equivalent that may be partially halogenated,
(b) fluorinating the hydrocarbon precursor to provide a perfluorinated intermediate,
(c) converting the perfluorinated intermediate to its corresponding perfluorinated acid metal salt, and
(d) converting the perfluorinated acid metal salt to its corresponding perfluorovinyl ether.
As used herein, the term perfluorinated means that all of the carbon bonded hydrogen atoms have been replaced with fluorine and any unsaturated carbon—carbon bonds have been saturated with fluorine.
In a first embodiment of the process of the invention, an appropriate hydrocarbon (e.g., containing at least one 2-alkoxy propionate moiety, derivative or equivalent) precursor is provided which includes a hydrocarbon acid derivative. Such derivatives include, for example, acid fluorides, anhydrides, esters and the like. This derivative is then perfluorinated to provide a corresponding perfluorinated acid derivative intermediate. The intermediate is then converted to its corresponding perfluorinated acid metal salt and subsequently converted to the desired perfluorovinyl ether.
In a second embodiment of the invention, a partially fluorinated hydrocarbon precursor is provided by reacting hexafluoropropylene oxide with an alcohol or a species such as sodium alkoxide. The precursor is then fully fluorinated by replacing any remaining carbon bonded hydrogen atoms with fluorine atoms to provide a perfluorinated acid derivative intermediate. The intermediate is then converted to its corresponding perfluorinated metal salt and subsequently converted to the desired perfluorovinyl ether.
In a third embodiment of the invention, a partially fluorinated hydrocarbon precursor is provided by reacting a fluorinated olefin with an alcohol, 2) fully fluorinating the precursor, 3) hydrolyzing the fluorinated precursor to an acid derivative, 4) converting the acid derivative to its corresponding perfluorinated acid metal salt, 5) converting the salt product to its corresponding perfluorovinyl ether.
In a fourth embodiment of the invention a perfluorovinyl ether having the formula R
f
OCF
2
OCF═CF
2
is provided wherein R
f
is as described above.
DETAILED DESCRIPTION
The perfluorinated vinyl ethers prepared according to the present invention are useful in the preparation of fluoroelastomers, especially those that are used at low temperatures. Such elastomers are known. See, for example, Uschold et al., U.S. Pat. No. 4,513,128.
The embodiment selected is not critical to the practice of the invention. However, there are certain process steps common to each of the embodiments of the invention.
Fluorination of the precursors may be accomplished by either electrochemical fluorination (ECF) or direct fluorination (DF). ECF is described in U.S. Pat. No. 2,713,593 and WO 98/50603. DF is described in U.S. Pat. No. 5,488,142.
Conversion of the perfluorinated precursor to the metal salt is preferably accomplished by treatment with a base, e.g. saponification.
Conversion of the perfluorinated metal salt to the vinyl ether is preferably accomplished by pyrolysis. Typically this is done by drying the salt and then heating the salt to a temperature of from 170° C. to 250° C. with or without the presence of a solvent or other medium.
The following discussion specifically addresses three embodiments of the invention. It is not intended to limit the scope of the disclosure to these embodiments. Rather it illustrates the versatility of the process.
In the first embodiment of the invention, the perfluorovinyl ether may be prepared by
(a) providing a hydrocarbon ester, anhydride, acid halide or acid precursor which comprises at least one 2-alkoxypropionate moiety, derivative or equivalent,
(b) fluorinating the precursor to provide a perfluorinated acid derivative intermediate,
(c) converting the perfluorinated intermediate to its perfluorinated metal salt, and
(d) pyrolyzing the perfluorinated metal salt to the corresponding perfluorovinyl ether.
More specifically, the first embodiment may be exemplified by the following synthesis sequence:
where R
h
is a C
1
-C
20
alkyl or aromatic group, which may be linear, branched, cyclic and which may contain additional ether linkages. The X
h
moiety is selected from the group consisting of R
h
, lower alkoxy, (such as —OCH
3
, —OCH
2
CH
3
), OC(O)CH(CH
3
)OR
h
, —F and —Cl. R
f
is a perfluorinated version of R
h
and X
f
is a perfluorinated version of X
h
.
In the case where a divinyl ether is desired, a precursor may be represented as
R′
h
(OCH(CH
3
)C(O)X
h
)
2
where R′
h
is described in a similar manner to R
h
above except it is divalent. The R
h
moieties in this particular precursor may be the same or different. Such a divinyl ether is CF
2
═CFOR′
f
OCF═CF
2
wherein
Guerra Miguel A.
Hare Erik D.
Hintzer Klaus
Moore George G. I.
Qiu Zai-Ming
Dyneon LLC
Lilly James V.
Shaver Paul F.
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