Low temperature fluorocarbon elastomers

Details Low temperature fluorocarbon elastomers Low temperature fluorocarbon elastomers

1999-05-18

2001-09-25

Lipman, Bernard (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

Reexamination Certificate

active

06294627

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the preparation of fluorocarbon polymeric and cured elastomeric materials containing perfluoroether units, particularly repeating units derived from perfluoroalkylvinyl ether compounds.
BACKGROUND OF THE INVENTION
Fluorocarbon elastomers are synthetic elastomeric polymers with a high fluorine content. See, for example, W. M. Grootaert et al., “Fluorocarbon Elastomers”, Kirk-Othmer, Encyclopedia of Chemical Technology, Vol 8, pp. 900-1005 (4th ed., John Wiley & Sons, 1993). Fluorocarbon elastomers, particularly the copolymers of vinylidene fluoride (VF2) with other ethylenically unsaturated halogenated monomers, such as C
3
F
6
(hexafluoropropylene or HFP), have become the polymers of choice for high temperature applications, such as seals, gaskets, and linings, especially when shaped articles thereof are subject to exposure to aggressive or harsh environments, such as solvents, lubricants, and oxidizing or reducing conditions. See, for example, U.S. Pat. No. 4,912,171 (Grootaert et al.), which discloses a fluoroelastomeric polymer prepared from VF2, tetrafluoroethylene (TFE), and a copolymerizable hydrocarbon olefin.
A major drawback to many applications of shaped articles made of such fluorocarbon elastomers has been their inability to satisfactorily function at low temperatures. Typically, at temperatures only slightly below 0° C., shaped articles made from copolymers of VF2 and HFP become stiff and fail to perform satisfactorily.
Low temperature flexibility of VF2 elastomers may be improved by substituting perfluoro(allyl vinyl ethers) for the HFP in VF2/HFP/TFE copolymers as discussed in U.S. Pat. No. 5,214,106 (Carlson et al.). Polymers of perfluorovinyl ethers or copolymers with LTE are also discussed in U.S. Pat. No. 3,817,960 (Resnick).
Cured perfluoroelastomers may be provided that exhibit enhanced low temperature properties through the incorporation by conventional compounding techniques of a selected perfluoropolyether into the perfluoroelastomer compound as discussed in U.S. Pat. No. 5,268,405 (Ojakaar et al.). A higher than normal loading of such additives may be accomplished by using a compatibility extender such as discussed in U.S. Pat. No. 3,632,788 (Stivers et al.). These additives are not permanently incorporated into the polymers and can be lost during post treatment and use of the shaped articles.
Many other fluorinated ethers have been described in the literature. One type is characterized by one of several homopolymeric segments or blocks of repeating units of the formula —CF(CF
3
)CF
2
—O— made from hexafluoropropylene oxide. Another type is that characterized by blocks of repeating units of the formula —CF
2
CF
2
—O— made from tetrafluoroethylene oxide. Others, made by reacting oxygen with tetrafluoroethylene or hexafluoropropylene, are characterized by a backbone of repeating —CF
2
O—, —CF(CF
3
)CF
2
O—, or —CF(CF
3
)O— units, a backbone of randomly distributed —CF
2
O— and —CF
2
CF
2
O— units, a backbone of —CF(CF
3
)CF
2
O— and —CF
2
CF
2
O—units and optionally a, —CF
2
O— and —CF(CF
3
)O— units. Another type of fluorinated ether is that characterized by backbone units of the formula —(CF
2
)
a
O(CF
2
)
b
— made by photopolymerization.
A peroxide-vulcanizable, fluorine-containing elastomer can be attained by copolymerizing a perfluoro(vinylether) compound represented by the general formula: CF
2
═CFO(CF
2
CF(CF
3
)O)
m
(CF
2
)
n
X, wherein X is a bromine atom or an iodine atom and m and n each are 1, 2 or 3; and a fluorine-containing olefin having 2 to 8 carbon atoms in the presence of an iodine and bromine-containing compound represented by the general formula: RBr
n
I
m
, wherein R is a fluorohydrocarbon group, a chlorofluorohydrocawbon group, a chlorohydrocarbon group or a hydrocarbon group, and n and m each are 1 or 2 as disclosed in U.S. Pat. No. 5,225,504 (Tatsu et al.).
None of these materials, however, have sufficient low temperature flexibility, particularly flexibility at temperatures as low as −50° C. or lower.
SUMMARY OF THE INVENTION
The present invention provides a fluorocarbon polymer which includes: repeating units derived from one or more perfluorinated ethers of the formula CF
2
═CFO—(CF
2
)
m
—(O(CF
2
)
p
)
n
—OR
f
1
wherein R
f
1
is a perfluorinated (C
1
-C
4
)alkyl group, m=1-4, n=0-6, and p=1-2; and repeating units derived from vinylidene fluoride; wherein the polymer has a glass transition temperature of −50° C. or lower and an oxygen to carbon ratio of at least about 0.2. Preferably, when m is 2 or 3 in the above formula, n is not 0.
The fluorocarbon polymer preferably further includes an effective amount (preferably, 0.2-5 mole-%) of cure site moieties derived from one or more compounds of the formulae: a) CX
2
═CX(Z), wherein (i) X is H or F; and (ii) Z is Br, I, or R
f
2
U wherein U=Br, I, or CN and R
f
2
=a perfluorinated divalent linking group optionally containing O atoms; and (b) Y(CF
2
)
q
Y, wherein: (i) Y is Br or I; and (ii) q=1-6.
The present invention also provides an elastomeric polymer prepared from a crosslinkable composition comprising a fluorocarbon polymer as described above. The crosslinkable composition can further include a free radical initiator, such as a peroxide initiator, a co-curing agent, such as a triallyl isocyanurate, and/or one or more fillers. The elastomeric polymer can be used to make seals, hoses, diaphragms, coatings, etc.
The present invention further provides methods of preparing an elastomeric polymer as described above. A preferred method includes: (a) providing a crosslinkable composition comprising a fluorocarbon polymer, the polymer comprising: i) repeating units derived from one or more perfluorinated ethers of the formula (Formula I): CF
2
═CFO—(CF
2
)
m
—(O(CF
2
)
p
)
n
—OR
f
1
wherein R
f
1
is a perfluorinated (C
1
-C
4
)alkyl group, m=1-4, n=0-6, and p=1-2; ii) repeating units derived from vinylidene fluoride; and iii) 0.2-5 mole-% of cure site moieties derived from one or more compounds of the formulae: CX
2
═CX(Z), wherein: X is H or F; and Z is Br, I, or R
f
2
U wherein U=Br, I, or CN and R
f
2
=a perfluorinated divalent linking group optionally containing O atoms; and Y(CF
2
)
q
Y, wherein: Y is Br or I; and q=1-6; wherein the polymer has a glass transition temperature of −50° C. or lower and an oxygen to carbon ratio of at least about 0.2; and (b) subjecting the crosslinkable composition to conditions effective to at least partially cure it. Preferably, the step of subjecting the crosslinkable composition to conditions effective to at least partially cure it includes applying heat and pressure and/or subjecting the composition to radiation.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to the preparation of fluorocarbon polymers, particularly curable fluorocarbon polymers having cure site, cured elastomers, and the processes for their curing. These materials have a variety of uses. The fluorocarbon polymers can be cured to provide fluorocarbon elastomers for use in seals, gaskets, hoses, diaphragms, linings, and other shaped articles, that have improved performance characteristics, particularly flexibility, at low temperatures. They can also be used as coatings. Even if not cured, these materials can be used in caulk or as diluents in thermoplastics, for example, to provide enhanced low temperature properties.
Preferably, the fluorocarbon polymers are prepared from perfluoroalkylvinyl ether and vinylidene fluoride, and have a Tg of less than about −50° C., and more preferably, less than about −60° C. Herein, particularly in the claims, Tg is defined as the midpoint on the curve obtained from a differential scanning calorimeter (DSC) analysis of the polymer using ASTM E1356-91 (Reapproved 1995). For certain of the examples in the Examples Section, the Tg values are slightly lower than would be obtained if this method were used. These values were obtained using

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