Patent Publication Number: US-2021189111-A1

Title: Curable fluoroelastomer composition

Description:
BACKGROUND 
     Fluoropolymers are a commercially important class of materials that include, for example, crosslinked and uncrosslinked fluorocarbon elastomers and semi-crystalline or glassy fluorocarbon plastics. 
     Fluorocarbon elastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated and non-halogenated monomers, such as hexafluoropropene, have particular utility in high temperature applications, such as seals, gaskets, and linings. See, for example, R. A. Brullo, “Fluoroelastomer Rubber for Automotive Applications,”  Automotive Elastomer  &amp;  Design , June 1985, “Fluoroelastomer Seal Up Automotive Future,”  Materials Engineering , October 1988, and W. M. Grootaert, et al., “Fluorocarbon Elastomers,” Kirk-Othmer,  Encyclopedia of Chemical Technology , Vol. 8, pp. 990-1005 (4 th  ed., John Wiley &amp; Sons, 1993). 
     SUMMARY 
     There is a desire to identify a novel curing system for partially fluorinated fluoropolymers. In one aspect, a curable partially fluorinated polymer composition is disclosed comprising: 
     (i) a partially fluorinated fluoropolymer, wherein the partially fluorinated amorphous fluoropolymer comprises carbon-carbon double bonds or is capable of forming carbon-carbon double bonds along the partially fluorinated amorphous fluoropolymer; and 
     (ii) a crosslinking component comprising a fluorinated sulfonamide polyol of the formula: 
     
       
         
         
             
             
         
       
     
     wherein
 
R f  is a fully or partially fluorinated group;
 
each R 1  is independently selected from alkylene or oxyalkylene or poly(oxyalkylene), and each R 2  is R 1 —OH, H, alkyl or aryl; and
 
subscript c is 1 or 2,
 
with the proviso that the curing component has at least two R 1 —OH groups.
 
     It will be understood that the polyols of Formula I include the alkali, alkali-earth metals and other salts thereof. Such salts may be prepared as described in U.S. Pat. No. 5,681,881 (Jing et al.), incorporated herein by reference. 
     In another aspect, an article comprising the cured composition described above is disclosed. 
     In yet another aspect a method of making a partially fluorinated elastomer is disclosed comprising curing the curable partially fluorinated polymer composition disclosed above. 
     As used herein, “alkyl” and “alkylene” mean the monovalent and divalent residues remaining after removal of one and two hydrogen atoms, respectively, from a linear or branched chain hydrocarbon having 1 to 20 carbon atoms. Examples of “alkyl” as used herein include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, norbornyl and the like. Unless otherwise noted, alkyl groups may be mono- or polyvalent. 
     “Fluorinated” refers to hydrocarbon compounds that have one or more C—H bonds replaced by C—F bonds; 
     “Fluoroalkyl has essentially the meaning as “alkyl” except that one or more of the hydrogen atoms of the alkyl radical are replaced by fluorine atoms. 
     “Fluoroalkylene has essentially the meaning as “alkylene” except that one or more of the hydrogen atoms of the alkyl radical are replaced by fluorine atoms. 
     “Perfluoroalkyl” has essentially the meaning as “alkyl” except that all or essentially all of the hydrogen atoms of the alkyl radical are replaced by fluorine atoms, e.g. perfluoropropyl, perfluorobutyl, perfluorooctyl, and the like. 
     “Perfluoroalkylene” has essentially the meaning as “alkylene” except that all or essentially all of the hydrogen atoms of the alkylene radical are replaced by fluorine atoms, e.g., perfluoropropylene, perfluorobutylene, perfluorooctylene, and the like 
    
    
     DETAILED DESCRIPTION 
     In the present disclosure, it has been found that a partially fluorinated fluoropolymer can be cured with a fluorinated polyol compound of Formula I and the conjugate base thereof. 
     The fluoropolymers of the present disclosure are partially fluorinated polymers. As disclosed herein, an amorphous partially fluorinated polymer is a polymer comprising at least one carbon-hydrogen bond and at least one carbon-fluorine bond on the backbone of the polymer. In one embodiment, the partially fluorinated polymer is highly fluorinated, wherein at least 60, 70, 80, or even 90% of the polymer backbone comprises C—F bonds. 
     The fluoropolymer of the present disclosure also comprises carbon-carbon double bonds and/or is capable of forming carbon-carbon double bonds along the polymer chain. In one embodiment, the partially fluorinated fluoropolymer comprises carbon-carbon double bonds along the backbone of the partially fluorinated fluoropolymer or is capable of forming carbon-carbon double bonds along the backbone of the partially fluorinated fluoropolymer. In another embodiment, the partially fluorinated fluoropolymer comprises carbon-carbon double bonds or is capable of forming carbon-carbon double bonds in a pendent group off of the backbone of the partially fluorinated fluoropolymer. 
     The fluoropolymer capable of forming carbon-carbon double bonds means that the fluoropolymer contains units capable of forming double bonds. Such units include, for example, two adjacent carbons, along the polymer backbone or pendent side chain, wherein a hydrogen is attached to the first carbon and a leaving group is attached to the second carbon. During an elimination reaction (e.g., thermal reaction, and/or use of acids or bases), the leaving group and the hydrogen leave forming a double bond between the two carbon atoms. An exemplary leaving group includes: a fluoride, an alkoxide, a hydroxide, a tosylate, a mesylate, an amine, an ammonium, a sulfide, a sulfonium, a sulfoxide, a sulfone, and combinations thereof. Those fluoropolymers capable of forming carbon-carbon bonds generally have the structure ˜CH—CX˜, where the tilde is a bond and X is a leaving groups such that when treated with base will provide the requisite unsaturation. In many embodiments the polymer has ˜CH—CF˜ in the backbone, which may be dehydrofluorinated. 
     The fluoropolymer comprises a plurality of these groups (carbon-carbon double bonds or groups capable of forming double bonds) to result in a sufficient cure. Generally, this means at least 0.1, 0.5, 1, 2, or even 5 mol %; at most 7, 10, 15, or even 20 mole % (i.e., moles of these carbon-carbon double bonds or precursors thereof per mole of polymer). 
     In one embodiment, the amorphous partially fluorinated polymer is derived from at least one hydrogen containing monomer such as vinylidene fluoride. 
     In one embodiment, the amorphous fluoropolymer comprises adjacent copolymerized units of vinylidene fluoride (VDF) and hexafluoropropylene (HFP); copolymerized units of VDF (or tetrafluoroethylene) and a fluorinated comonomer capable of delivering an acidic hydrogen atom to the polymer backbone, such as trifluoroethylene; vinyl fluoride; 3,3,3-trifluoropropene-1; pentafluoropropene (e.g., 2-hydropentafluoropropylene and 1-hydropentafluoropmpylene); 2,3,3,3-tetrafluoroproperie; and combinations thereof. 
     In some embodiments, small amounts (e.g., less than 10, 5, 2, or even 1 wt %) of additional monomers may be added so long as the amorphous fluoropolymer is able to be cured using the curing agent disclosed herein. 
     In one embodiment, the amorphous fluoropolymer is additionally derived from a hydrogen containing monomer including: pentafluoropropylene (e.g., 2-hydropentafluropropylene), propylene, ethylene, isobutylene, and combinations thereof. 
     In one embodiment, the amorphous fluoropolymer is additionally derived from a perfluorinated monomer. Exemplary perfluorinated monomers include: hexafluoropropene; tetrafluoroethylene; chlorotrifluoroethylene; perfluoro(alkylvinyl ether) such as perfluoromethyl vinyl ether, CF 2 ═CFOCFCF 2 CF 2 OCF 3 , CF 2 ═CFOCF 2 OCF 2 CF 2 CF 3 , CF 2 ═CFOCF 2 OCF 2 CF 3 , CF 2 ═CFOCF 2 OCF 3 , and CF 2 ═CFOCF 2 OC 3 F 7 , perfluoro(alkylallyl ether) such as perfluoromethyl allyl ether, perfluoro(alkyloxyallyl ether) such as perfluoro-4,8-dioxa-1-nonene (i.e., CF 2 ═CFCF 2 O(CF 2 ) 3 OCF 3 , and combinations thereof. 
     Exemplary types of polymers include those comprising interpolymerized units derived from (i) vinylidene fluoride, tetrafluoroethylene, and propylene; (ii) vinylidene fluoride, tetrafluoroethylene, ethylene, and perfluoroalkyl vinyl ether, such as perfluoro(methyl vinyl ether); (iii) vinylidene fluoride with hexafluoropropylene; (iv) hexafluoropropylene, tetrafluoroethylene, and vinylidene fluoride; (v) hexafluoropropylene and vinylidene fluoride, (vi) vinylidene fluoride and perfluoroalkyl vinyl ether; (vii) vinylidene fluoride, tetrafluoroethylene, and perfluoroalkyl vinyl ether, (viii) vinylidene fluoride, perfluoroalkyl vinyl ether, hydropentafluoroethylene and optionally, tetrafluoroethylene; (ix) tetrafluoroethylene, propylene, and 3,3,3-trifluoroproperte; (x) tetrafluoroethylene, and propylene; (xi) ethylene, tetrafluoroethylene, and perfluoroalkyl vinyl ether, and optionally 3,3,3-trifluoropropylene; (xii) vinylidene fluoride, tetrafluoroethylene, and perfluoroalkyl allyl ether, (xiii) vinylidene fluoride and perfluoroalkyl allyl ether; (xiv) ethylene, tetrafluoroethylene, and perfluoroalkyl vinyl ether, and optionally 3,33-trifluoropropylene; (xv) vinylidene fluoride, tetrafluoroethylene, and perfluoroalkyl allyl ether, (xvi) vinylidene fluoride and perfluoroalkyl allyl ether; (xvii) vinylidene fluoride, tetrafluoroethylene, and perfluoroalkyloxyallyl ether, (xviii) vinylidene fluoride and perfluoroalkyloxyallyl ether; (xiv) vinylidene fluoride, tetrafluoroethylene, and perfluoroalkyloxyallyl ether, (xv) vinylidene fluoride and perfluoroalkyloxyallyl ether; and (xvi) combinations thereof. 
     Advantageously, by using the curing agent disclosed herein, the amorphous fluoropolymers of the present disclosure can be cured without the need for pendent bromine, iodine, or nitrile cure sites along the polymer backbone. Often, the iodine and bromine-containing cure site monomers, which are polymerized into the fluoropolymer and/or the chain ends, can be expensive among other things. 
     The amorphous fluoropolymer of the present disclosure is substantially free of I, Br, and nitrile groups, wherein the amorphous fluoropolymer comprises less than 0.1, 0.05, 0.01, or even 0.005 mole percent relative to the total polymer. 
     In one embodiment, the amorphous fluoropolymers of the present disclosure are non-grafted, meaning that they do not comprise pendant groups including vinyl, allyl, acrylate, amido, sulfonic acid salt, pyridine, carboxylic ester, carboxylic salt, hindered silanes that are aliphatic or aromatic tri-ethers or tri-esters. In one embodiment, the amorphous fluoropolymer does not comprise a monophenol graft. 
     The above described amorphous fluoropolymers may be blended with one or more additional crystalline fluoropolymers. With the instant curing compounds, the crystalline fluoropolymers may be cured into the matrix of the amorphous fluoropolymer 
     Commercially available crystalline fluoropolymers include, for example, those fluoropolymers having the trade designation “THV” (e.g., “THV 200”, “THV 400”, “THV 500”, “THV 610”, or “THV 800”) as marketed by Dyneon, St. Paul, Minn.; “KYNAR” (e.g., “KYNAR 740”) as marketed by Atofina, Philadelphia, Pa.; “HYLAR” (e.g., “HYLAR 700”) as marketed by Ausimont USA, Morristown, N.J.; and “FLUOREL” (e.g., “FLUOREL FC-2178”) as marketed by Dyneon. 
     Useful fluoropolymers also include copolymers of HFP, TFE, and VDF (i.e., THV). These polymers may have, for example, VDF monomeric units in a range of from at least about 2, 10, or 20 percent by weight up to 30, 40, or even 50 percent by weight, and HFP monomeric units in a range of from at least about 5, 10, or 15 percent by weight up to about 20, 25, or even 30 percent by weight, with the remainder of the weight of the polymer being TFE monomeric units. Examples of commercially available THV polymers include those marketed by Dyneon, LLC under the trade designations “3M DYNEON FLUOROPLASTIC THV 221GZ”, “3M DYNEON FLUOROPLASTIC THV 221AZ”, “3M DYNEON FLUOROPLASTIC THV 415GZ”, “3M DYNEON FLUOROPLASTIC THV 815GZ”, “3M DYNEON FLUOROPLASTIC THV 500GZ”, “3M DYNEON FLUOROPLASTIC THV 610GZ”, “3M DYNEON FLUOROPLASTIC ET 6218Z”, “3M DYNEON FLUOROPLASTIC ET 6235Z”, “DYNEON FLUOROTHERMOPLASTIC THV 2030G”, “DYNEON FLUOROTHERMOPLASTIC THV 220”, “DYNEON FLUOROTHERMOPLASTIC THV 415”, “DYNEON FLUOROTHERMOPLASTIC THV 500A”, “DYNEON FLUOROTHERMOPLASTIC THV 610G”, or “DYNEON FLUOROTHERMOPLASTIC THV 810G”. 
     Useful fluoropolymers also include copolymers of ethylene, TFE, and HFP. These polymers may have, for example, ethylene monomeric units in a range of from at least about 2, 10, or 20 percent by weight up to 30, 40, or even 50 percent by weight, and HFP monomeric units in a range of from at least about 5, 10, or 15 percent by weight up to about 20, 25, or even 30 percent by weight, with the remainder of the weight of the polymer being TFE monomeric units. Such polymers are marketed, for example, under the trade designation “DYNEON FLUOROTHERMOPLASTIC HTE” (e.g., “DYNEON FLUOROTHERMOPLASTIC HTE X 1510” or “DYNEON FLUOROTHERMOPLASTIC HTE X 1705”) by Dyneon LLC. 
     Useful fluoropolymers also include copolymers of tetrafluoroethylene and propylene (TFE/P). These copolymers may have, for example, TFE monomeric units in a range of from at least about 20, 30 or 40 percent by weight up to about 50, 65, or even 80 percent by weight, with the remainder of the weight of the polymer being propylene monomeric units. Such polymers are commercially available, for example, under the trade designations “AFLAS” (e.g., “AFLAS TFE ELASTOMER FA 100H”, “AFLAS TFE ELASTOMER FA 150C”, “AFLAS TFE ELASTOMER FA 150L”, or “AFLAS TFE ELASTOMER FA 150P”) as marketed by Dyneon, LLC, or “VITON” (e.g., “VITON VTR-7480” or “VITON VTR-7512”) as marketed by E.I. du Pont de Nemours &amp; Company, Wilmington, Del. 
     Useful fluoropolymers also include copolymers of ethylene and TFE “ETFE”). These copolymers may have, for example, TFE monomeric units in a range of from at least about 20, 30 or 40 percent by weight up to about 50, 65, or even 80 percent by weight, with the remainder of the weight of the polymer being propylene monomeric units. Such polymers may be obtained commercially, for example, as marketed under the trade designation “DYNEON FLUOROTHERMOPLASTIC ET 6235” by Dyneon LLC. 
     VDF-containing fluoropolymers can be prepared using emulsion polymerization techniques as described, for example, in U.S. Pat. No. 4,338,237 (Sulzbach et al.) or U.S. Pat. No. 5,285,002 (Grootaert), the disclosures of which are incorporated herein by reference. 
     The curable composition further comprises a fluorinated sulfonamide polyol curing agent of the formula: 
     
       
         
         
             
             
         
       
     
     wherein
 
R f  is a fully or partially fluorinated group;
 
each R 1  is independently a (hetero)hydrocarbyl group selected from alkylene, ether or polyether (oxyalkylene or poly(oxyalkylene)), and each R 2  is H, alkyl or aryl; and
 
subscript c is 1 or 2,
 
with the proviso that the crosslinking component has at least two R 1 —OH groups.
 
     In some embodiments R 1  and/or R 2  may comprise an ether or a polyether of the formula —(R 5 O) y R 5 —, where R 5  is an alkylene group having from 2 to about 4 carbon atoms, such as —CH 2 CH 2 —, —CH 2 CH 2 CH 2 —, —CH(CH 3 )CH 2 —, and —CH(CH 3 )CH(CH 3 )—, and y is a number between about 1 and about 15 inclusive. The oxyalkylene units in said polyether can be the same, such as in poly(oxypropylene) or poly(oxyethylene), or can be present as a mixture, such as in a straight or branched chain of randomly distributed oxyethylene and oxypropylene units, i.e., poly(oxyethylene-co-oxypropylene), or as in straight or branched chain blocks of oxypropylene units. 
     The ether group is terminated for example with a hydroxyl to provide the R 1 —OH, or the R 2  may be terminated with a with a C 1 -C 15  alkyl group, an aryl group or combination thereof. 
     Specific examples of ether/polyether groups include:
     —(CH 2 CH 2 O) y C 8 H 17 ,   —(CH 2 CH 2 O) y H,   —(CH 2 CH 2 O) y CH[CH 2 CH(CH 3 ) 2 ][CH 2 CH(CH 3 )CH 2 CH(CH 3 ) 2 ],   —(CH 2 CH 2 O) y C 10 H 21 ,   —(CH 2 CH 2 OyC 6 H 4 —C(CH 3 ) 2 —CH 2 —C(CH 3 ) 3 ,   —(CH 2 CH(CH 3 )O) y CH 2 CH 3 ], and   —(CH 2 CH(CH 3 )O) y H, wherein y is 1-15.   

     It will be appreciated that Formula I include compounds of the formula; 
     
       
         
         
             
             
         
       
     
     where
 
R f  is a fully or partially fluorinated group; each R 1  is independently a (hetero)hydrocarbyl group selected from alkylene, ether or polyether; and
 
subscript c is 1 or 2.
 
     Compounds of Formula I will also include compounds of the formula 
     
       
         
         
             
             
         
       
     
     R f  is a fully or partially fluorinated group;
 
each R 4  is a (hetero)hydrocarbyl group selected from H, monovalent aryl, alkyl or ether, polyether or —R 1 —OH.
 
     The R f  groups can contain straight chain, branched chain, or cyclic polyvalent perfluorinated groups in any combination and are of the general formula: —C n F 2n   −  for divalent groups, —C n F 2n-1 — for trivalent groups, —C n F 2n-2 — for tetravalent groups, etc. Divalent groups with n=3 to 8 being more preferred and with n=2 to 5 being the most preferred. The compounds of Formula I will include the corresponding salts, or conjugate bases. 
     Minor amounts of hydrogen or chlorine atoms can also be present as substituents, provided that no more than one atom of either is present for every two carbon atoms. Preferably the R f  group is entirely perfluorinated. 
     The perfluoroalkylene groups may comprise 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms. A typical divalent perfluoroalkylene is —CF 2 —CF 2 —, —CF 2 —CF 2 —CF 2 —, —CF(CF 3 )—CF 2 —, —CF 2 —, —CF 2 —CF 2 —CF 2 —CF 2 —CF 2 —CF 2 —, cyclic —C 6 F 12 — or CF(CF 3 )—. 
     In some embodiments the R f  group may be selected from perfluoroether groups:
     [R f   13 —O—R f   14 —(R f   15 ) q ]—[(CH 2 ) y —OH] x , IV where   [R f   13 —O—R f   14 —(R f   15 ) q ] has a valence of x from abstraction of two or more F atoms from any of the R f   13 , R f   14 , or R f   15  groups,   R f   13  represents a perfluoroalkylene group,   R f   14  represents a perfluoroalkyleneoxy group,   R f   15  represents a perfluoroalkylene group and q is 0 or 1   subscript y is 1 to 8; and   subscript xis 2 to 4.   

     Compounds of Formulas I-III are generally prepared by alkylation of the corresponding fluorinated sulfonamides, which in turn are prepared by reaction of the fluorinated sulfonyl fluorides with ammonia. Reference may be made to U.S. Pat. Nos. 2,803,656, 2,732,398 (Brice), U.S. Pat. No. 4,533,713 (Howells) and U.S. Pat. No. 9,725,683 (Lamanna et al.), each incorporated herein by reference. 
     Compounds of Formula I in which R 2  is not R 1 —OH may be prepared by a first reaction of a fluorinated sulfonyl fluoride with an amine of the formula R 2 —NH 2 , followed by a second alkylation of the sulfonamide product with a compound of the formula X—R 1 —OH, where X is a leaving groups such as halide or tosylate. Alternatively, a sulfonamide may be sequentially alkylated with R 2 —X and X—R 1 —OH, in either order. It will be understood that a mixture of products of Formula I will result. 
     The curing agent should be used in quantities substantial enough to cause the amorphous fluoropolymer to cure, as indicated by a rise in torque on a moving die rheometer. For example, at least 0.5-20 parts of the crosslinking agent per 100 parts of the amorphous fluoropolymer is used. If too little curing agent is used, the amorphous fluoropolymer will not cure. If too much curing agent is used, the amorphous fluoropolymer can become brittle. For example, no more than 20 millimoles of the curing agent per 100 parts of the amorphous fluoropolymer is used. One or a blend of polyol compounds with Formula I may be used. 
     In addition to the polyol curing agents of Formula I, the curable composition may optionally include a second, optional crosslinking agent. Examples of the optional crosslinking agent include polyol compounds, polythiol compounds, polyamine compounds, amidine compounds, bisaminophenol compounds, oxime compounds, and the like. In some embodiments, the second crosslinking agent may comprise a non-fluorinated hydrocarbyl polyol analogous to Formula I. 
     Generally, examples are not restricted for selecting the specific combination of the sulfonamides of Formula I and secondary crosslinking agent and/or crosslinking promoter, depending on the type of polymer, but typical examples are presented below. For example, with a vinylidene fluoride system (binary system or ternary system), a polyol compound, polyamine compound, polythiophen compound is preferable. With a tetrafluoroethylene-propylene-vinylidene fluoride-based fluorine rubber (ternary) system, polyol compound, polyamine compound, polythiol compound, or the like is preferable. 
     Examples of preferable polyol compounds include 2,2-bis(4-hydroxyphenyl) hexafluoropropane, 4,4′-dihydroxy diphenyl sulfone, 4,4′-diisopropylidene diphenol, and the like. 
     Examples of preferable polythiol compounds include 2-dibutyl amino-4,6-dimercapto-s-triazine, 2,4,6-trimercapto-s-triazine, and the like. 
     Examples of preferable polyamine compounds include hexamethylene diamine carbamate, N,N′-dicinnamylidene-1,6-hexanediamine, 4,4′-methylene bis(cyclohexylamine) carbonate, and the like. 
     Examples of preferable amidine compounds include p-toluene sulfonate salts of 1,8-diazabicyclo[5.4.0]undec-7-ene, and the like. 
     Examples of preferable bisaminophenol compounds include 2,2-bis(3-amino-4-hydroxyphenyl))-hexafluoropropane, 2,2-bis[3-amino-4-(N-phenylamino) phenyl]hexafluoropropane, and the like. 
     In some embodiments, a combination of polyols of Formula I may be combined with a secondary fluorinated compounds of the Formula Z-Q-R f —O—(R fo )R f -Q-Z, as described in U.S. Pat. Nos. 5,384,374 and 5,266,650, Guerra et al, each incorporated herein by reference. 
     If using an optional second crosslinking agent, the molar ratios of the polyol curing agent of Formula I to the second crosslinking agent may be from 5:1 to 1:1. 
     The curable composition may further comprise an acid acceptor including organic, inorganic, or blends of thereof. Examples of inorganic acceptors include magnesium oxide, lead oxide, calcium oxide, calcium hydroxide, dibasic lead phosphate, zinc oxide, barium carbonate, strontium hydroxide, calcium carbonate, hydrotalcite, etc. Organic acceptors include amines, epoxies, sodium stearate, and magnesium oxalate. Particularly suitable acid acceptors include calcium hydroxide, magnesium oxide and zinc oxide. Blends of acid acceptors may be used as well. The amount of acid acceptor will generally depend on the nature of the acid acceptor used. 
     If the presence of an extractable metal compound is not desirable (such as semiconductor applications), the use of inorganic acid acceptors should be minimized, and these preferably should not be used at all. For example, a hardening composition with a formula that does not use an inorganic acid acceptor is particularly useful for sealing materials and gaskets for manufacturing semiconductor elements, sealing materials that are in contact with water, hot water, or the like, and sealing materials for high temperature areas such as automotive applications. 
     Examples of preferred acid acceptors that are commonly used include zinc oxide, calcium hydroxide, calcium carbonate, magnesium oxide, hydrotalcite, silicon dioxide (silica), lead oxide, and the like. These compounds are generally used in order to bond with HF and other acids. These acids are possibly produced at high temperatures that can be encountered during the hardening process when molding a molded article using the fluoropolymer composition, or at temperatures that demonstrate the function of fluoropolymers and the like. 
     In one embodiment, at least 0.5, 1, 2, 3, or even 4 parts of the acid acceptor per 100 parts of the amorphous fluoropolymer are used. In one embodiment, no more than 10, 7, or even 5 parts of the acid acceptor per 100 parts of the amorphous fluoropolymer are used. 
     The curable composition may further comprise an organo onium compound added to the composition as a phase transfer catalyst to assist with the crosslinking of the amorphous fluoropolymer and/or may be used to generate the double bonds on the fluoropolymer through dehydrofluorination. Such organo onium compounds include quaternary ammonium hydroxides or salts, quaternary phosphonium hydroxides or salts, and ternary sulfonium hydroxides or salts. 
     Briefly, a phosphonium and ammonium salts or compounds comprise a central atom of phosphorous or nitrogen, respectively, covalently bonded to four organic moieties by means of a carbon-phosphorous (or carbon-nitrogen) covalent bonds and is ionically associated with an anion. The organic moieties can be the same or different. 
     Briefly, a sulfonium compound is a sulfur-containing organic compound in which at least one sulfur atom is covalently bonded to three organic moieties having from 1 to 20 carbon atoms by means of carbon-sulfur covalent bonds and is ionically associated with an anion. The organic moieties can be the same or different. The sulfonium compounds may have more than one relatively positive sulfur atom, e.g. [(C 6 H 5 ) 2 S + (CH 2 ) 4 S + (C 6 H 5 ) 2 Cl − , and two of the carbon-sulfur covalent bonds may be between the carbon atoms of a divalent organic moiety, i.e., the sulfur atom may be a heteroatom in a cyclic structure. 
     Many of the organo-onium compounds useful in this invention are described and known in the art. See, for example, U.S. Pat. No. 4,233,421 (Worm), U.S. Pat. No. 4,912,171 (Grootaert et al.), U.S. Pat. No. 5,086,123 (Guenthner et al.), and U.S. Pat. No. 5,262,490 (Kolb et al.), U.S. Pat. No. 5,929,169, all of whose descriptions are herein incorporated by reference. Another class of useful organo-onium compounds include those having one or more pendent fluorinated alkyl groups. Generally, the most useful fluorinated onium compounds are disclosed by Coggio et al. in U.S. Pat. No. 5,591,804. 
     Exemplary organo onium compounds include: C 3 -C 6  symmetrical tetraalkylammonium salts, unsymmetrical tetraalkylammonium salts wherein the sum of alkyl carbons is between 8 and 24 and benzyltrialkylammonium salts wherein the sum of alkyl carbons is between 7 and 19 (for example tetrabutylammonium bromide, retrabutylammonium chloride, benzyltributylammonium chloride, benzyltriethylammonium chloride, tetrabutylammonium hydrogen sulfate and tetrabutylammonium hydroxide, phenyltrimethylammonium chloride, tetrapentylammonium chloride, tetrapropylammonium bromide, tetrahexylammonium chloride, and tetraheptylammonium bromidetetramethylammonium chloride); quaternary phosphonium salts, such as tetrabutylphosphonium salts, tetraphenylphosphonium chloride, benzyltriphenylphosphonium chloride, tributylallylphosphonium chloride, tributylbenzyl phosphonium chloride, tributyl-2-methoxypropylphosphonium chloride, benzyldiphenyl(dimethylamino)phosphonium chloride, 8-benzyl-1,8-diazobicyclo[5.4.0]7-undecenium chloride, benzyltris(dimethylamitio)phosphonium chloride, and bis(benzyldiphenylphosphine)iminium chloride. Other suitable organo onium compounds include 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene. Phenolate is a preferred anion for the quaternary ammonium and phosphonium salts. 
     In one embodiment, the organo onium compound is used between 1 and 5 millimoles per 100 parts of the amorphous fluoropolymer (mmhr). 
     The fluoropolymer composition can also contain various additives in addition to the aforementioned components. Examples of additives include crosslinking auxiliary agents and/or crosslinking promoting auxiliary agents that combine favorably with the crosslinking agent and/or crosslinking promoter used, fillers (such as carbon black, flowers of zinc, silica, diatomaceous earth, silicate compounds (clay, talc, wollastonite, and the like), calcium carbonate, titanium oxide, sedimentary barium sulfate, aluminum oxide, mica, iron oxide, chromium oxide, fluoropolymer filler, and the like), plasticizers, lubricants (graphite, molybdenum disulfide, and the like), release agents (fatty acid esters, fatty acid amides, fatty acid metals, low molecular weight polyethylene, and the like), colorants (cyanine green and the like), and processing aids that are commonly used when compounding fluoropolymer compositions, and the like. However, these additives are preferably sufficiently stable under the intended conditions of use. 
     Furthermore, the carbon black can be used to achieve a balance between fluoropolymer composition properties such as tensile stress, tensile strength, elongation, hardness, wear resistance, conductivity, processability, and the like. Preferable examples include MT blacks under the product numbers N-991, N-990, N-908, and N-907 (medium thermal black); FEF N-550; and large diameter furnace black, and the like. If carbon black is used, the amount is preferably from approximately 0.1 to approximately 70 mass parts (phr) based on 100 mass parts of the total amount of polymer containing fluorinated olefin units and the additional polymer. This range is particularly preferable for the case where large particle furnace black is used 
     The curable amorphous fluoropolymer compositions may be prepared by mixing the amorphous fluoropolymer, the curing agent, along with the other components (e.g., the acid acceptor, the onium compound, and/or additional additives) in conventional rubber processing equipment to provide a solid mixture, i.e. a solid polymer containing the additional ingredients, also referred to in the art as a “compound”. This process of mixing the ingredients to produce such a solid polymer composition containing other ingredients is typically called “compounding”. Such equipment includes rubber mills, internal mixers, such as Banbury mixers, and mixing extruders. The temperature of the mixture during mixing typically will not rise above about 120° C. During mixing the components and additives are distributed uniformly throughout the resulting fluorinated polymer “compound” or polymer sheets. The “compound” can then be extruded or pressed in a mold, e.g., a cavity or a transfer mold and subsequently be oven-cured. In an alternative embodiment curing can be done in an autoclave. 
     Curing is typically achieved by heat-treating the curable amorphous fluoropolymer composition. The heat-treatment is carried out at an effective temperature and effective time to create a cured fluoroelastomer. Optimum conditions can be tested by examining the cured fluoroelastomer for its mechanical and physical properties. Typically, curing is carried out at temperatures greater than 120° C. or greater than 150° C. Typical curing conditions include curing at temperatures between 160° C. and 210° C. or between 160° C. and 190° C. Typical curing periods include from 3 to 90 minutes. Curing is preferably carried out under pressure. For example, pressures from 10 to 100 bar may be applied. A post curing cycle may be applied to ensure the curing process is fully completed. Post curing may be carried out at a temperature between 170° C. and 250° C. for a period of 1 to 24 hours. 
     The partially fluorinated amorphous fluoropolymer in the curable composition has a Mooney viscosity in accordance with ASTM D1646-06 TYPE A by a MV 2000 instrument (available from Alpha Technologies, Ohio, USA) using large rotor (ML 1+10) at 121° C. Upon curing, using the curing agent disclosed herein, the amorphous fluoropolymer becomes an elastomer, becoming a non-flowing fluoropolymer, and having an infinite viscosity (and therefore no measurable Mooney viscosity). 
     The above curable compositions can be compounded or mixed in one or several steps, and then the mixture can be processed and shaped, for example, by extrusion (for example, in the form of a hose or hose lining) or molding (for example, in the form of an O-ring seal). The shaped article can then be heated to cure the composition and form a cured elastomer article. 
     In some embodiments the desired amounts of conventional additives adjuvants or ingredients are added to the uncured compositions and intimately admixed or compounded therewith by employing any of the usual rubber mixing devices such as Banbury mixers, roll mills, or any other convenient mixing device. The temperature of the mixture on the mill typically will not rise above about 120° C. During milling the components and adjuvants are distributed uniformly throughout the gum. The curing process typically comprises extrusion of the compounded mixture or pressing the compounded mixture in a mold, e.g., a cavity or a transfer mold, and subsequent oven-curing. Pressing of the compounded mixture (press cure) is usually conducted at a temperature between about 95 and about 230° C., preferably between about 150° C. and about 205° C. for a period of from 1 minute to 15 hours, typically from 5 minutes to 30 minutes. A pressure of between about 700 kPa and about 20,600 kPa is usually imposed on the compounded mixture in the mold. The molds first may be coated with a release agent, such as a silicone oil, and prebaked. The molded vulcanizate is then usually post-cured (oven-cured) at a temperature usually between about 150° C. and about 315° C. for a period of from about 2 hours to 50 hours or more depending on the cross-sectional thickness of the article. 
     The compositions of this invention can be used to form seals, O-rings and gaskets. The cured fluorocarbon elastomer mixture has excellent low-temperature flexibility while retaining the desired physical properties, for example tensile strength and elongation, of conventionally compounded and cured compositions. Particularly useful articles that can be fabricated from the fluorocarbon elastomer compositions of this invention are particularly useful as seals, gaskets, and molded parts in automotive, chemical processing, semiconductor, aerospace, and petroleum industry applications, among others. 
     EXAMPLES 
     Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Unless otherwise indicated, all other reagents were obtained, or are available from fine chemical vendors such as Sigma-Aldrich Company, St. Louis, Mo., or may be synthesized by known methods. Table 1 (below) lists materials used in the examples and their sources. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Materials List 
               
            
           
           
               
               
            
               
                 DESIGNATION 
                 DESCRIPTION 
               
               
                   
               
               
                 FC 2145 
                 A low-viscosity copolymer of hexafluoropropylene and vinylidene 
               
               
                   
                 fluoride that does not include an incorporated curative, available 
               
               
                   
                 under the trade designation “3M DYNEON FLUOROELASTOMER  
               
               
                   
                 FC 2145” from 3M Company, Maplewood, MN, USA. 
               
               
                 TPBPC 
                 Triphenylbenzyl phosphonium chloride, available from Sigma-Aldrich 
               
               
                   
                 (St. Louis, MO, USA), diluted to 50% by weight in methanol, also 
               
               
                   
                 available from Sigma-Aldrich. 
               
               
                 C1 
                 Bisphenol-AF, 2,2-Bis(4-hydroxyphenyl) hexafluoropropane, 
               
               
                   
                 available from Sigma-Aldrich. 
               
               
                 C5 
                 FBSEE Diol, C 4 F 9 —SO 2 —N(C 2 H 4 —OH) 2 , prepared as described in US 
               
               
                   
                 Patent application 2010/0160458, page 3, [0058]. 
               
               
                 C31 
                 3EO Diol, C 4 F 9 —SO 2 —N(C 2 H 4 —OH)(C 4 H 4 OC 2 H 4 —OH), prepared as 
               
               
                   
                 described in Synthesis 4 of US Pat. No. 9725683. 
               
               
                 C32 
                 4EO Diol, C 4 F 9 —SO 2 —N(C 2 H 4 OC 2 H 4 —OH) 2 , prepared as described in 
               
               
                   
                 Synthesis 3 of US Pat. No. 9725683. 
               
               
                 Ca(OH) 2   
                 An acid acceptor. Calcium hydroxide commercially available under 
               
               
                   
                 the trade designation “HALLSTAR CALCIUM HYDROXIDE HP-XL” 
               
               
                   
                 from The Hallstar Company, Chicago, IL, USA 
               
               
                 MgO 
                 An acid acceptor. Magnesium oxide powder commercially available 
               
               
                   
                 under the trade designation “ELASTOMAG 170” from Akrochem 
               
               
                   
                 Corp., Akron, OH, USA 
               
               
                 N990 
                 Carbon black, available under the trade designation “N990” from 
               
               
                   
                 Cancarb, Medicine Hat, Alberta, Canada 
               
               
                   
               
            
           
         
       
     
     Compounding 
     150 g batches of fluoropolymer were compounded with 0.78 parts per hundred resin (phr) of TPBPC, various amounts of curing agent as indicated in Table 2, 6 phr of Ca(OH) 2 , 3 phr of MgO, and 20 phr of N990 carbon black, using a two-roll mill. Milling continued until a homogeneous blend formed. Ca(OH) 2 , MgO, and N990 were added as a mixture. The ratios of each component in examples and comparative examples are indicated as phr in Table 2, below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Compounding 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 EXAMPLE 
                 CE-1 
                 EX-1 
                 EX-2 
                 EX-3 
                 EX-4 
                 EX-5 
                 EX-6 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 FC 2145, g  
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 TPBPC, phr 
                 0.78 
                 0.78 
                 0.78 
                 0.78 
                 0.78 
                 0.78 
                 0.78 
               
               
                 C1, phr 
                 2.02 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 C5, phr 
                 — 
                 2.32 
                 4.65 
                 — 
                 — 
                 — 
                 — 
               
               
                 C31, phr 
                 — 
                 — 
                 — 
                 2.59 
                 5.18 
                 — 
                 — 
               
               
                 C32, phr 
                 — 
                 — 
                 — 
                 — 
                 — 
                 2.85 
                 5.70 
               
               
                 Ca(OH) 2 , phr 
                 6 
                 6 
                 6 
                 6 
                 6 
                 6 
                 6 
               
               
                 MgO, phr 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
               
               
                 N990, phr 
                 20 
                 20 
                 20 
                 20 
                 20 
                 20 
                 20 
               
               
                   
               
            
           
         
       
     
     Cure Rheology 
     Cure rheology tests were carried out using uncured, compounded samples using a moving die rheometer (MDR) marketed under the trade designation RPA 2000 by Alpha technologies, Akron, Ohio, in accordance with ASTM D 5289-93a at 177° C. (pre-heated), 12 minute elapsed time, and a 0.5 degree arc. The minimum torque (ML), maximum torque (Mu), the time for the torque to reach a value equal to ML+0.5(M H −M L ), (t′50), and the time for the torque to reach ML+0.9(M H −M L ), (t′90), the scorch time (Ts2), and Tan delta at maximum torque were measured and their values are listed in Table 3. 
     Press-Cure Molding and Physical Property Test 
     The compound was press-cured using a mold (size: 75 millimeters (mm)×150 mm×2 mm or 150 mm×150 mm×2 mm) at 6.5×10 3  kilopascals (kPa) and 177° C. for 10 minutes. Then the elastomer sheets were removed, cooled to room temperature, and then used for physical property test and post-cure. The dog bone specimens were cutout from the sheets with ASTM Die D and subjected to physical property testing similar to the procedure disclosed in ASTM D412-06a (2013). The typical tensile strength deviation is +/−1.4 MPa (200 psi). The typical elongation deviation is +/−25%. Hardness is +/−2. Since this is a destructive test, it doesn&#39;t follow a normal bell shape distribution. It is Weibull distribution. The test results are summarized in Table 3. 
     Post-Cure and Physical Property Test 
     The press-cured elastomer sheet was post cured at 232° C. for 16 hours in a circulating air oven. The samples were then removed from the oven, cooled to room temperature, and physical properties determined. The dog bone specimens were cutout from the sheets with ASTM Die D and subjected to physical property testing similar to the procedure disclosed in ASTM D412-06a (2013). The test results are summarized in Table 3. 
     Heat-Aging and Physical Property Test 
     The dog bone specimens of post cured samples were placed in a circulating air oven for 70 hours at 270° C. The samples were then removed from the oven and cooled to room temperature for measurement of physical properties according to ASTM D412-06a (2013). The test results are summarized in Table 3. 
     O-Ring Molding and Compression Set Test 
     O-rings having a cross-section thickness of 0.139 inch (3.5 mm) were molded at 6.5×10 3  kPa and 177° C. for 10 minutes and then post-cured at 232° C. for 16 hours. The O-rings were subjected to compression set testing similar to the procedure disclosed in ASTM 395-89 method B (2008), with 25% initial deflection. Results of compression tests are reported in Table 3. The typical deviation is +/−2% to 3%. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Curable fluoropolymer curing characteristics,  
               
               
                 and properties of cured fluoropolymers 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 CE-1 
                 *EX-1 
                 **EX-2 
                 EX-3 
                 EX-4 
                 EX-5 
                 EX-6 
               
               
                   
               
            
           
           
               
            
               
                 Curing Characteristics 
               
               
                   
               
               
                 Moving Die Rheometer, 0.5° at 177° C. (350° F.) 12 minute motor 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Minimum torque, M L , N · m 
                 0.061 
                 0.242 
                 0.357 
                 0.100 
                 0.069 
                 0.068 
                 0.040 
               
               
                 Maximum torque, M H , N · m 
                 1.793 
                 0.568 
                 0.849 
                 0.509 
                 0.669 
                 0.610 
                 0.727 
               
               
                 M H -M L , N · m 
                 1.732 
                 0.326 
                 0.493 
                 0.409 
                 0.600 
                 0.541 
                 0.687 
               
               
                 Ts2, minutes 
                 0.62 
                 0.87 
                 0.6 
                 0.65 
                 0.59 
                 0.83 
                 1 
               
               
                 t′50, minutes 
                 0.73 
                 0.479 
                 0.67 
                 0.57 
                 0.7 
                 0.94 
                 1.38 
               
               
                 t′90, minutes 
                 1.06 
                 2.82 
                 2.79 
                 3.35 
                 3.16 
                 3.74 
                 5.53 
               
               
                 Tan delta at maximum torque 
                 0.042 
                 0.201 
                 0.093 
                 0.189 
                 0.106 
                 0.143 
                 0.11 
               
               
                   
               
            
           
           
               
            
               
                 Properties of Cured Gumstocks 
               
               
                   
               
               
                 Physical Properties, press cure 10 minutes at 177° C. (350° F.) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Durometer, shore A 
                 66 
                 * 
                 63 
                 57 
                 60 
                 58 
                 57 
               
               
                 Tensile, MPa 
                 10.2 
                 * 
                 9.7 
                 10.2 
                 9.8 
                 11.6 
                 9.7 
               
               
                 Elongation, % 
                 239 
                 * 
                 206 
                 558 
                 405 
                 504 
                 480 
               
               
                 100% Modulus, MPa 
                 3.3 
                 * 
                 3.4 
                 1.5 
                 2.1 
                 1.7 
                 1.6 
               
            
           
           
               
            
               
                 Physical Properties, post cure 16 hours at 232° C. (450° F.) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Durometer, shore A 
                 67 
                 * 
                 63 
                 63 
                 68 
                 62 
                 66 
               
               
                 Tensile, MPa 
                 14.1 
                 * 
                 11.0 
                 13.1 
                 15.1 
                 13.2 
                 14.4 
               
               
                 Elongation, % 
                 191 
                 ** 
                 190 
                 321 
                 214 
                 311 
                 244 
               
               
                 100% Modulus, MPa 
                 4.5 
                 ** 
                 4.0 
                 2.5 
                 4.8 
                 2.5 
                 4.2 
               
            
           
           
               
            
               
                 Physical Properties, heat aged 70 hours at 270° C. (518° F.) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Durometer, shore A 
                 74 
                 * 
                 68 
                 65 
                 79 
                 69 
                 78 
               
               
                 Tensile, MPa 
                 7.4 
                 * 
                 9.7 
                 10.1 
                 11.4 
                 11.5 
                 12.6 
               
               
                 Elongation, % 
                 151 
                 * 
                 218 
                 324 
                 134 
                 222 
                 123 
               
               
                 100% Modulus, MPa 
                 4.5 
                 * 
                 4.1 
                 2.5 
                 8.4 
                 4.3 
                 11.0 
               
            
           
           
               
            
               
                 Compression Set 70 hours at 200° C. (392° F.) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Compression Set, % 
                 21.1 
                 ** 
                 45 
                 62.7 
                 62 
                 67 
                 70.5 
               
               
                   
               
               
                 *Did not form a good molded product due to scorching; 
               
               
                 **Processable to form a molded sample, but some scorching observed 
               
            
           
         
       
     
     All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.