| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 03.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 21.03.00 |
| PATENT TITLE |
Base resistant fluorinated polymers |
| PATENT ABSTRACT |
Disclosed herein are copolymers of tetrafluoroethylene and n-alkyl trifluorovinyl ether which further contain either curesite repeat units and/or iodine. Such curesite repeat units, upon exposure to free radicals, may crosslink the copolymers. The iodine is introduced by carrying out free radical polymerization in the presence of an organic iodide chain transfer agent. The polymers according to the invention are especially useful as elastomers and/or as molding resins for articles or parts that may be exposed to a basic environment. The preparation of such polymers by aqueous emulsion polymerization is also disclosed. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 23.10.98 |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A polymer which is the product of free radically copolymerizing, in the presence of an organic iodide, a reaction mixture of monomers comprising tetrafluoroethylene, a compound of the formula CF.sub.2 .dbd.CFOR.sup.1, wherein R.sup.1 is an n-alkyl containing 1 to 6 carbon atoms, and, optionally, other free radically copolymerizable monomers, provided that: said polymer contains about 0.1 to about 5 percent by weight of iodine; and repeat unit (I), derived from tetrafluoroethylene, and repeat unit (II), derived from a compound of the formula CF.sub.2 .dbd.CFOR.sup.1, are at least 50 mole percent of the repeat units of said polymer. 2. The polymer as recited in claim 1 wherein R.sup.1 is ethyl, n-propyl or n-butyl. 3. The polymer as recited in claim 2 wherein R.sup.1 is n-butyl. 4. The polymer as recited in claim 1 wherein the molar ratio of (I):(II) is about 3:1 to about 13:7. 5. The polymer as recited in claim 1 which also contains one or more comonomers selected from the group consisting of vinylidene fluoride, hexafluoropropylene, and a perfluoro(alkyl vinyl ether), wherein the alkyl group contains 1 to 5 carbon atoms. 6. The polymer as recited in claim 1 which is an elastomer. 7. The polymer as recited in claim 1 which is crosslinked. 8. The polymer as recited in claim 1 which consists essentially of repeat units derived from repeat units derived from tetrafluoroethylene and a compound of the formula CF.sub.2 .dbd.CFOR.sup.1. 9. The polymer as recited in claim 1 which contain about 0.5 to about 2.5 percent by weight iodine. 10. The polymer as recited in claim 1 wherein said organic iodide is selected from the group consisting of CH.sub.2 I.sub.2, R.sup.4 I, where R.sup.4 is a perfluoroalkyl, and I(CH.sub.2 CH.sub.2).sub.p (CF.sub.2).sub.m (CH.sub.2 CH.sub.2).sub.p I, wherein m is 1-10, and each p is independently 0 or 1. 11. The polymer as recited in claim 10 wherein m is 2 or 4, and p is 0. 12. The polymer as recited in claim 1 which is not crosslinked. 13. The polymer as recited in claim 1 which has been crosslinked by contact with free radicals. 14. A polymer comprising the following repeat units: ##STR3## and a crosslink-functional repeat unit (III) by means of which the polymer is readily crosslinked upon exposure of said polymer to free radicals; wherein R.sup.1 is an alkyl containing 1 to 6 carbon atoms; provided that (I)+(II)+(III) are at least about 50 mole percent of the repeat units in said polymer, and further provided said polymer is not crosslinked. 15. A polymer comprising the following repeat units: ##STR4## and a crosslink-functional repeat unit (III) by means of which the polymer is readily crosslinked upon exposure of said polymer to free radicals; wherein R.sup.1 is an alkyl containing 1 to 6 carbon atoms; provided that (I)+(II)+(III) are at least about 50 mole percent of the repeat units in said polymer, and further provided said polymer has been crosslinked by contact with free radicals. |
| PATENT DESCRIPTION |
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. SUMMARY OF THE INVENTION This invention concerns a first polymer 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 molar ratio of [(I)+(II)]:(III) is about 200:1 to about 20:1. The repeat 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 to 80.degree. C. at a tetrafluoroethylene pressure of about 1 to 6 MPa. The present invention also concerns a second polymer, 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 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 (TFE), 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. Pat. No. 2,917,548, hereby incorporated by reference in its entirety. In a preferred embodiment, R.sup.1 in (II) and (V) are ethyl, n-propyl or n-butyl, more preferably n-butyl. If a polymer consisted only of repeat units (I) and (II), it could only be free radically crosslinked with relative difficulty. Repeat unit (III) enables the polymer to be readily crosslinked when exposed to free radicals (or sources of energy that create free radicals). The ability to readily form crosslinks at a sufficiently high level or concentration is important for elastomeric polymers, in order to provide good vulcanizate properties. In a preferred embodiment of the first kind of polymer according to the present invention, the polymer is an elastomer, i.e., a copolymer that is above its glass transition temperature and contains no appreciable amount of crystallinity at 20.degree. C., as measured by differential scanning calorimetry. Repeat units and monomers which readily enable crosslinking of fluoropolymers under free radical conditions are well known. See, for instance, U.S. Pat. Nos. 4,035,565, 4,564,662, 4,745,165, 4,694,045, 4,948,852, 4,973,633 and 5,173,553, all of which are hereby incorporated by reference in their entirety. Crosslink-functional monomers which are adapted to provide a reactive curesite for the polymer, include those that contain bromine in a side chain. Suitable bromine-containing curesite monomers include bromotetrafluorobutene, bromotrifluoroethylene, and brominated fluorovinyl ethers such as CF.sub.2 .dbd.CFOCF.sub.2 CF.sub.2 Br and CF.sub.3 CH.sub.2 OCF.dbd.CFBr. Free-radical crosslinking sites may also be found on repeat units which contain alkyl groups having at least 1 methine hydrogen atom (a hydrogen atom bound to a carbon atom which in turn is bound to three other carbon atoms) in a side chain, or which contain an alkyl ether group in a side chain, wherein the alkyl is substituted or unsubstituted. More than one repeat unit (III) that promotes free radical crosslinking of the polymer may be present. Preferred repeat units (III) are as follows: ##STR2## wherein i and k is an integer in the range of 2 to 10, preferably 2 or 4, j is an integer in the range of 1 to 4, preferably 1, and each R.sup.2 is independently an alkyl group containing 1 to 4 carbons. It is preferred if both R.sup.2 groups are methyl. The monomers for preferred repeat unit (IIIA) can be made by methods described in P. Tarrant, et al., J. Org. Chem., vol. 34, p. 864ff (1969). The monomers which polymerize to form the above repeat units (IIIB) and (IIIC) can be made by the reaction of an alkoxide of the corresponding alcohol with tetrafluoroethylene, as will be readily appreciated by the skilled artisan. Preferably, in the above-described polymers, the molar ratio of (I):(II) is about 3:1 to about 13:7, and/or the molar ratio of [(I)+(II)]:(III) is about 130:1 to about 70:1. In the first polymer according to the present invention, up to 50 mole percent of the repeat units may be units other than (I), (II), and (III). These other units may be derived from a wide variety of known monomers which free radically copolymerize with the monomers from which repeat units (I), (II) and (III) are derived. For examples of such known monomers, see, for instance, W. Gerhartz, et al., Ed., Ullmann's Encyclopedia of Industrial Chemistry, vol. A11, at p. 393-429 (VCH Verlagsgesellschaft mbH, Weinheim 5th Ed. 1988); and H. F. Mark, et al., Ed., Encyclopedia of Polymer Science and Technology, at p. 577-648 (John Wiley & Sons, New York 3d Ed. 1989), of which the cited pages are hereby incorporated by reference. Accordingly, suitable optional comonomers include vinylidene fluoride, hexafluoropropylene, perfluoro(alkyl vinyl ether), preferably wherein the alkyl group contains 1 to 5 carbon atoms, especially perfluoro(methyl vinyl ether). Preferably, the optional repeat units are present in the first polymer in an amount of less than 35 mole percent of the repeat units of the first polymer. More preferably, the first polymer consists essentially of repeat units (I), (II) and (III). The first polymers according to the present invention may be prepared by free radical polymerization using methods known to the skilled artisan. See, for instance, W. Gerhartz, et al., Ed., Ullmann's Encyclopedia of Industrial Chemistry, vol. A11, at p. 393-429 (VCH Verlagsgesellschaft mbH, Weinheim, 5th Ed. 1988); and H. F. Mark, et al., Ed., Encyclopedia of Polymer science and Technology, at 577-648 (John Wiley & Sons, New York 3d Ed. 1989). These polymers may be made by batch, semi-batch or continuous processes, employing solution, aqueous, non-aqueous suspension, or emulsion polymerization processes. Such polymers should preferably be of sufficient molecular weight so that a useful crosslinkable elastomer can be formed, although lower molecular weights may also be useful, for example, as crosslinkable caulks. Preferably, the first or second polymers according to the present invention is made by an aqueous emulsion polymerization carried out at about 30 to 80.degree. C., preferably about 35 to 45.degree. C., and most preferably about 40.+-.5.degree. C. in a semi-batch or continuous mode, at a TFE pressure of about 1-6 MPa, preferably 1-3 MPa. Such a polymerization is illustrated by Example 12 herein. The first polymers according to the present invention may be in a crosslinked or uncrosslinked form. These polymers may be crosslinked by mixing them with a suitable amount of at least one free radical generator, typically about 1 to about 10 weight percent of the generator in the reaction mixture, and heating to generate free radicals and hence crosslink. As the artisan will readily understand, free radicals should be generated which are of sufficiently high energy to cause crosslinking. Suitable free radical generators include 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane (available as Lupersol.RTM./Luperco.RTM. 101XL from Atochem, Inc.), 2,5-dimethyl-2,5-bis-t-butylperoxy)hex-3-yne (available as Lupersol.RTM./Luperco.RTM. 130XL from Atochem, Inc.), di-t-butyl peroxide, and dicumyl peroxide. Suitable coagents, such as triallyl isocyanurate or trimethallyl isocyanurate, may also be used to improve the efficiency of crosslinking by the radical generator. The second polymer of the present invention is a polymer which is made by free radical polymerization of TFE (IV) and CF.sub.2 .dbd.CFOR.sup.1 (V), wherein R.sup.1 is an alkyl group containing 1 to 6 carbon atoms. In this case, R.sup.1 preferably contains 2 to 4 carbon atoms. It is also preferred that R.sup.1 is n-alkyl. It is especially preferred that R.sup.1 is n butyl. The polymerization to make the second polymer is carried out by essentially the same methods employed to prepare the first polymer disclosed herein (see above), except that an organic iodide must be present and the monomer for making repeat unit (III) may not necessarily be present. The organic iodide acts as a chain transfer agent, thereby resulting in iodine atoms becoming part of the product polymer. The product polymer contains about 0.1 to about 5 weight percent of iodine, preferably about 0.5 to about 2.5 weight percent of iodine. For listings of such iodides, and how such iodides are used, see U.S. Pat. Nos. 4,158,678, 4,243,770, 4,948,852 and 4,973,633, which are hereby incorporated by reference. Preferred iodides are R.sup.4 I, wherein R.sup.4 is perfluoroalkyl, CH.sub.2 I.sub.2, and I(CH.sub.2 CH.sub.2).sub.p (CF.sub.2).sub.m (CH.sub.2 CH.sub.2).sub.p I, wherein m is 1-10, preferably 2, and each p is independently 0 or 1, preferably 0. The weight percent of iodine in the polymer may be measured as described in Analytical Chemistry, vol. 22, p. 1047ff (1950). The iodine analyses reported herein were done by Schwartzkopf Microanalytical Laboratories using this method. The second polymer according to the present invention is preferably elastomeric. This second polymer may optionally contain up to 50 mole percent of repeat units derived from monomers other than TFE (IV) and CF.sub.2 .dbd.CFOR.sup.3 (V). The optional and preferred monomers listed above for the first polymer are also optional and preferred for the second polymer. In addition, any of the repeat units (III) mentioned above may be present in the second polymer (as part of the optional repeat units). The preferred repeat units (III) mentioned above are also the preferred optional repeat units in the second polymer. The second polymer herein may be crosslinked or uncrosslinked. The polymer may be free radically crosslinked by methods described above for the first polymer. Polymers according to the present invention, of both the first and second kind described herein, are useful as elastomers and molding resins for making parts which require heat and chemical, especially base, resistance. When used as thermoplastic molding resins, the polymers may be crosslinked during molding by incorporating a free radical generating agent that decomposes at the molding temperatures. If the polymer is elastomeric, however, it is preferably crosslinked during, for example, molding or extrusion, as is done with most elastomers. The resulting parts are useful, for example, in gaskets and seals, including o-rings, especially where chemical and temperature resistance, particularly base resistance, is required. These polymers are especially useful when used in contact with certain basic fluids, such as monoamines and polyamines. Except where noted, all pressures in the following Examples are gauge pressures. The following abbreviations are used in the Examples: ______________________________________ BTFB 4-bromo-3,3,4,4-tetrafluorobut-1-ene BuFVE n-butyl trifluorovinyl ether DSC Differential Scanning Calorimetry TFE tetrafluoroethylene T.sub.g glass transition temperature TGA ThermoGravimetric Analysis ______________________________________ |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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