Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1997-12-03
1998-12-22
Smith, Jeffrey T.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526206, 526249, C08F 1624
Patent
active
058521500
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Disclosed herein are polymers derived from tetrafluoroethylene, an alkyl trifluorovinyl ether, and a curesite monomer and/or an organic iodide compound. A process for preparing such polymers is also disclosed. Such polymers are especially useful as base resistant elastomers.
TECHNICAL BACKGROUND
Fluoropolymers are generally well known for their chemical and thermal resistance. Partially fluorinated polymers, however, usually have some weakness towards certain types of chemicals, particularly bases. Such polymers often undergo dehydrofluorination or other reactions in the presence of bases, making them unsuitable for use in basic environments. This is particularly true for partially fluorinated polymers which are elastomers, since they are often used as seals for systems which are basic. For this reason, partially fluorinated polymers which are relatively stable to bases have been sought.
U.S. Pat. No. 3,159,609 describes copolymers of tetrafluoroethylene (TFE) and alkyl trifluorovinyl ethers. These polymers are not described as being readily crosslinkable.
U.S. Pat. Nos. 4,158,678, 4,243,770, 4,948,852 and 4,973,633 describe the use of organic iodides as chain transfer agent in fluoromonomer polymerizations. None of these references teach the polymers of this invention.
U.S. Pat. No. 3,525,724 describes polymers containing repeat units derived from tetrafluoroethylene, alkyl trifluorovinyl ethers, and the repeat unit --CF.sub.2 C(O)--. Such polymers are not free radically crosslinkable, as defined herein.
SUMMARY OF THE INVENTION
This invention concerns a first polymer, which is not crosslinked, comprising the repeat units ##STR1## and a crosslink-functional repeat unit (III), which enables said polymer to readily crosslink upon exposure of said polymer to free radicals, wherein R.sup.1 is an alkyl group containing 1 to 6 carbon atoms. Preferably, the molar ratio of (I):(II) is about 4:1 to about 1:1, and the units (I)+(II)+(III) are, in combination, about 50 mole percent or more of the repeat units making up the polymer.
In the above formulas, the repeat unit (I) can be derived from the monomer tetrafluoroethylene (IV), and the repeat unit (II) can be derived from a monomer of the formula CF.sub.2 .dbd.CFOR.sup.3 (V).
A novel process for preparing the above-described polymer is also disclosed, which process comprises reacting an admixture of monomers comprising at least 50 mole percent of a combination of tetrafluoroethylene, at least one monomer within the formula CF.sub.2 .dbd.CFOR.sup.1, and at least one crosslink-functional comonomer, wherein the polymerization process is carried out in an aqueous emulsion at a temperature of from about 30.degree. to 80.degree. C. at a tetrafluoroethylene pressure of about 1 to 6 MPa.
The present invention also concerns a second polymer, which is not crosslinked, which is made by free radically copolymerizing, in the presence of an organic iodide, the following monomers: tetrafluoroethylene (IV), a compound of the formula CF.sub.2 .dbd.CFOR.sup.1 (V), wherein R.sup.1 is alkyl containing 1 to 6 carbon atoms, and, optionally, other free radically copolymerizable monomers, such that the polymer product contains about 0.1 to about 5 percent by weight of iodine. The monomers (IV) and (V) react to form, respectively, repeat units (I) and (II), as defined above, which repeat units, in combination, are at least 50 mole percent of the repeat units making up the polymer product.
DETAILS OF THE INVENTION
The present invention includes two kinds of copolymers which which are useful as base resistant elastomers and which contain a repeat unit derived from a trifluorovinyl ether monomer. The first polymer described herein has three necessary repeat units, herein labelled (I), (II) and (III). Unit (I) is derived from tetrafluoroethylene (TEE), while repeat unit (II) is derived from a trifluorovinyl ether monomer of the formula CF.sub.2 .dbd.CFOR.sup.1 (V). The monomer from which repeat unit (II) is derived may be made by the method described in U.S.
REFERENCES:
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E. I. Du Pont de Nemours and Company
Sarafim N.
Smith Jeffrey T.
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