Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-11
2003-12-02
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S326400, C525S359200, C525S195000, C525S200000, C524S424000
Reexamination Certificate
active
06657012
ABSTRACT:
TECHNICAL FIELD
This invention relates to fluoropolymer compositions having nitrile group-containing cure-site components.
BACKGROUND
Fluorine-containing polymers (also known as “fluoropolymers”) are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers, and semi-crystalline or amorphous fluoroplastics. Fluoroplastics are generally of high thermal stability and are particularly useful at high temperatures. They may also exhibit extreme toughness and flexibility at very low temperatures. Some have very low dielectric loss and high dielectric strength, and may have unique low friction properties.
Fluoroelastomers exhibit significant tolerance to high temperatures and harsh chemical environments. Consequently, they are particularly well-adapted for use as seals, gaskets, and other molded parts in systems that are exposed to elevated temperatures and/or corrosive chemicals. Such parts are widely used in the chemical processing, semiconductor, aerospace, and petroleum industries, among others.
Fluoroelastomers often include a cure-site component to facilitate cure in the presence of a catalyst. One class of useful cure-site components includes nitrile group-containing monomers. Organotin catalysts are typically used as cure catalysts. Such catalysts, however, are toxic and can leave undesirable extractable metal residues in the cured product.
SUMMARY
In one aspect, the invention relates to a composition that includes (a) a fluoropolymer having interpolymerized units derived from a cure site monomer comprising a nitrile group; and (b) a catalyst composition that includes a compound having the formula:
where M is a divalent metal, X is an anionic group, and n is 2 to 6, preferably 3 to 5.
In yet another aspect, the invention provides a method for curing this composition, as well as the cured compositions.
The compositions retain the advantages of the use of nitrile group-containing cure site monomers such as the high temperature performance properties and chemical resistance typically achieved when organotin compounds are used as the catalyst system with such cure site monomers. At the same time, the compositions exhibit markedly improved compression set values. The compositions are useful in applications where polymer stability (e.g., thermal stability) and/or chemical resistance are important. They are also useful in silicon wafer fabrication.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims.
DETAILED DESCRIPTION
Suitable fluoropolymers include interpolymerized units derived from a nitrile group-containing monomer and, preferably, at least two principal monomers. Examples of suitable candidates for the principal monomer include perfluoroolefins (e.g., tetrafluoroethylene and hexafluoropropene), perfluorovinyl ethers (e.g., perfluoroalkyl vinyl ethers and perfluoroalkoxy vinyl ethers), and hydrogen-containing monomers such as olefins (e.g., ethylene, propylene, and the like) and partially-fluorinated olefins such as vinylidene fluoride.
Suitable perfluorinated vinyl ethers include those of the formula:
CF
2
═CFO(R′
f
O)
a
(R″
f
O)
b
R
f
(1)
wherein R′
f
and R″
f
are the same or are different linear or branched perfluoroalkylene groups of 1-6 carbon atoms; a and b are, independently, 0 or an integer from 1 to 10; and R
f
is a perfluoroalkyl group of 1-6 carbon atoms.
A preferred class of perfluoroalkyl vinyl ethers includes compositions of the formula:
CF
2
═CFO(CF
2
CFXO)
n
R
f
(2)
where: X is F or CF
3
; n is 0-5, and R
f
is a perfluoroalkyl group of 1-6 carbon atoms.
Most preferred perfluoroalkyl vinyl ethers are those where, in reference to either Formula 1 or 2 above, n is 0 or 1 and R
f
contains 1-3 carbon atoms. Examples of such perfluorinated ethers include perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.
Other useful perfluorinated monomers include those compounds of the formula:
CF
2
═CFO[(CF
2
)
m
(CFZ)
u
O]
n
R
f
(3)
where R
f
is a perfluoroalkyl group having 1-6 carbon atoms, m is 0-2, u is 0 or 1, n is 0-5, provided that both m and n are not zero, and Z is F or CF
3
. Preferred members of this class are those in which R
f
is C
3
F
7
or CF
3
, m is 0, and n is 1.
Additional perfluoroalkyl vinyl ether monomers useful in the invention include those of the formula:
CF
2
═CFO[(CF
2
CF(CF
3
)O)
g
(CF
2
)
k
(OCF
2
)
p
]C
x
F
2x+1
(4)
where g is 0 or an integer from 1-10, k is an integer of from 1-6, p is 0-3, and x is 1-5, provided that when k is 0, p is also 0. Preferred members of this class include compounds where n is 0 or 1, m is 0 or 1, and x is 1.
Perfluoroalkoxy vinyl ethers useful in the invention include those of the formula:
CF
2
═CFO(CF
2
)
t
(CFZ)
u
O(CF
2
O)
w
C
x
F
2x+1
(5)
wherein Z is F or CF
3
, t is 1-3, u is 0-1, w is 0-3, and x is 1-5, preferably 1. Specific, representative, examples of useful perfluoroalkoxy vinyl ethers include CF
2
═CFOCF
2
OCF
2
CF
2
CF
3
, CF
2
═CFOCF
2
OCF
3
, CF
2
═CFO(CF
2
)
3
OCF
3
, and CF
2
═CFOCF
2
CF
2
OCF
3
.
Mixtures of perfluoroalkyl vinyl ethers and perfluoroalkoxy vinyl ethers may also be employed.
Perfluoroolefins useful in the invention include those of the formula:
CF
2
═CF—R
5
f
, (6)
where R
5
f
is fluorine or a perfluoroalkyl of 1 to 8, preferably 1 to 3, carbon atoms.
In addition, partially-fluorinated monomers or hydrogen-containing monomers such as olefins (e.g., ethylene, propylene, and the like), and vinylidene fluoride can be used in the fluoropolymer of the invention.
One example of a useful fluoropolymer is composed of tetrafluoroethylene and at least one perfluoroalkyl vinyl ether as principal monomer units. In such copolymers, the copolymerized perfluorinated ether units constitute from about 15 to about 50 mole percent (mol %) (more preferably 15 to 35 mol %) of total monomer units present in the polymer.
One or more other fluoropolymers may be incorporated into the fluoropolymer having interpolymerized units derived from a cure site monomer comprising a nitrile group. In addition, one or more other fluoropolymers (which may include one or more copolymers) may be blended with the fluoropolymer (which may comprise a copolymer) having interpolymerized units derived from a cure site monomer comprising a nitrile group. Such other fluoropolymers useful in a blend and/or copolymer include the entire array described above. The other fluoropolymer(s) may lack interpolymerized units derived from a cure site monomer comprising a nitrile group and/or may include reactive sites adapted to a selected curative system. For example, two different fluoropolymers, each having interpolymerized units derived from a cure site monomer comprising a nitrile group may be blended to provide the fluoropolymer for the present invention.
Another fluoropolymer may be included along with another curative, such as described below, to provide particular properties. For example, a fluoropolymer suitable for peroxide curing and a peroxide curative may be included to improve chemical stability. Such a blend balances the thermal stability and the chemical stability of the resultant blend, and also may provide economic benefits. These other curatives also may be used to cure a blend of nitrile-containing fluoropolymers without the need to include a fluoropolymer lacking nitrile groups.
The fluoropolymers may be prepared by methods known in the art. For example, the polymerization process can be carried out by any free-radical polymerization of the monomers, e.g., as solutions, emulsions, or dispersions in an organic solvent or water. Polymerization in an aqueous emulsion or suspension often is preferred because of the rapid and nearly complete conversion of monomers, easy remova
Grootaert Werner M. A.
Kolb Robert E.
3M Innovative Properties Company
Harts Dean M.
Wilson D. R.
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