Fluoroelastomer composition having excellent processability and low temperature properties

FIELD OF THE INVENTION
 This invention relates to fluoroelastomers that are capable of being
 crosslinked with polyhydroxy compounds to produce cured compositions
 having excellent processability and low temperature properties.
 BACKGROUND OF THE INVENTION
 Elastomeric fluoropolymers (i.e. fluoroelastomers) exhibit excellent
 resistance to the effects of heat, weather, oil, solvents and chemicals.
 Such materials are commercially available and are most commonly either
 dipolymers of vinylidene fluoride (VF.sub.2) with hexafluoropropylene
 (HFP) or terpolymers of VF.sub.2, HFP, and tetrafluoroethylene (TFE).
 While these di- and terpolymers have many desirable properties, including
 low compression set and excellent processability, their low temperature
 flexibility is not adequate for all applications.
 It is known that incorporation of per fluorinated ether monomer units into
 vinylidene fluoride elastomers improves low temperature properties. For
 example, Carlson, in U.S. Pat. No. 5,214,106 discloses that when
 perfluoro(methyl vinyl) ether (PMVE) is substituted for HFP, the resultant
 VF.sub.2 /PMVE/TFE copolymers have glass transition temperature (T.sub.g)
 values which are 10.degree.-20.degree. C. lower than those of the
 corresponding VF.sub.2 /HFP/TFE copolymers. T.sub.g is often used as an
 indicator of low temperature flexibility because polymers having low glass
 transition temperatures maintain elastomeric properties at low
 temperatures.
 Kruger, in U.S. Pat. No. 5,696,216, discloses PMVE-containing
 fluoroelastomers that are similar to those disclosed by Carlson. Those
 disclosed by Kruger contain copolymerized units of VF.sub.2 ; at least one
 fluorinated propene and or fluorinated methyl vinyl ether; TFE; at least
 one perfluoro(polyoxyalkyl vinyl) ether, and a crosslinking site.
 The compositions of Carlson and Kruger are most effectively crosslinked
 through use of peroxide cure systems. However, when compression molding
 equipment is used with peroxide curable VF.sub.2 /PMVE copolymers the
 compositions generally exhibit a tendency to stick to and foul the mold.
 Tetrapolymers of VF.sub.2, HFP, TFE and perfluoro(alkyl vinyl) ethers
 (PAVE) other than PMVE are also known to exhibit improved low temperature
 properties compared to terpolymers of VF.sub.2, HFP and TFE. For example,
 Arcella, et al. in U.S. Pat. No. 5,260,393 disclose a tetrapolymer
 comprising copolymerized units of 48-65 wt. % VF.sub.2, 21-36 wt. % HFP,
 3-9 wt. % PAVE, and 0-17 wt. % TFE. The compositions can be cured using a
 bisphenol curing system and do not exhibit the mold fouling problems
 associated with peroxide cures of VF.sub.2 /PMVE copolymers. Similarly,
 British Patent 1,296,084 discloses fluoroelastomeric tetrapolymers
 containing copolymerized units of 48-65 wt. % VF.sub.2, 8-23 wt. % HFP,
 4-15 wt. % TFE, and 17-30 wt. % PAVE. Such compositions have good low
 temperature properties and are curable with bisphenols or amines. Although
 these tetrapolymers exhibit good low temperature properties, many
 applications require improved low temperature and processability
 performance.
 Merely raising the PAVE content while lowering the HFP content is not a
 solution to the problem of improving low temperature performance of
 VF.sub.2 /HFP/PAVE/TFE terpolymers. This is because polymers wherein the
 level of HFP is below about 8-10 mole percent do not contain sufficient
 copolymerized monomer sequences consisting of HFP units flanked by
 VF.sub.2 units to permit efficient crosslinking with bisphenols. As is
 well known in the art, efficient curing of VF.sub.2 /HFP-containing
 fluoroelastomers with a bisphenol/accelerator system is possible only when
 a --CH.sub.2 -- group in the polymer backbone is flanked by two
 perfluorinated carbons (e.g. CF.sub.2 CF(CF.sub.3)CH.sub.2 CF.sub.2
 CF.sub.2), rendering the hydrogens acidic enough to be abstracted by base.
 The dehydrofluorinated polymers are easily crosslinked by bisphenols.
 Furthermore, as discussed by W. W. Schmiegel, in Angewandte
 Makromolekulare Chemie, 76/77, 39 (1979), completely eliminating HFP to
 form VF.sub.2 /TFE/PMVE terpolymers results in formation of monomer
 sequences consisting of TFE/VF.sub.2 /TFE; TFE/VF.sub.2 /PMVE;
 PMVE/VF.sub.2 /PMVE; and PMVE/VF.sub.2 /TFE. Although such sites readily
 undergo elimination of HF or HOCF.sub.3 in the presence of base, the
 double bonds thus formed are not easily crosslinked by bisphenols or any
 other traditional crosslinking agents.
 There thus exists an unfulfilled need in the art for a method of providing
 copolymers of VF.sub.2, TFE, and PAVE that maintain optimum low
 temperature properties, but which exhibit low mold sticking
 characteristics, improved processability and are easily curable.
 SUMMARY OF THE INVENTION
 The present invention is directed to a fluoroelastomer consisting
 essentially of copolymerized units of 23-65 weight percent vinylidene
 fluoride, 25-75 weight percent perfluoro(alkyl vinyl) ether, 0-30 weight
 percent tetrafluoroethylene, and 0.3-5 weight percent
 2-hydropentafluoropropene.
 In addition, the invention is directed to a curable composition comprising
 A. a fluoroelastomer consisting essentially of copolymerized units of 23-65
 weight percent vinylidene fluoride, 25-75 weight percent perfluoro(alkyl
 vinyl) ether, 0-30 weight percent tetrafluoroethylene, and 0.3-5 weight
 percent 2-hydro-pentafluoropropene;
 B. a polyhydroxy crosslinking agent;
 C. a cure accelerator; and
 D. a metal oxide or metal hydroxide.
 A preferred embodiment of the curable compositions of the invention
 additionally comprises a modified silane coated mineral filler.
 A further preferred embodiment of the curable compositions of the invention
 additionally comprises a molecular sieve.
 DETAILED DESCRIPTION OF THE INVENTION
 The polymers of the present invention include both uncured (raw) and cured
 fluorinated copolymers. The copolymers are capable of undergoing
 crosslinking reactions with polyhydroxylic compounds to form elastomeric
 compositions that exhibit unusually good low temperature properties.
 The polymer backbones of the copolymers consist essentially of
 copolymerized units of VF.sub.2, PAVE, 2-hydropentafluoropropene (i.e.
 1,1,3,3,3-pentafluoropropene), referred to herein as HPFP, and,
 optionally, TFE. That is, each of the first three monomers (and optionally
 TFE) must be present in the polymer chain, but higher order polymers, i.e.
 those containing other additional monomer units, the addition of which
 does not affect the basic and novel characteristics of the polymer, are
 also within the scope of the present invention. For example, the
 tetrapolymer VF.sub.2 /PAVE/TFE/HPFP can contain other copolymerized vinyl
 or olefin monomers such as vinyl fluoride, trifluoroethylene,
 trifluoropropene, chlorotrifluoroethylene, alkyl vinyl ether, vinyl
 acetate, vinyl chloride, ethylene, and propylene, generally in quantities
 of up to about 5 wt. %. In addition, the fluoroelastomer copolymers of
 this invention may contain up to about 1 wt. % iodine bound to polymer
 chain ends, the iodine being introduced via use of an iodine-containing
 chain transfer agent during polymerization.
 The fluoroelastomers of the invention contain between 23-65 wt. %
 copolymerized vinylidene fluoride units, preferably between 33-55 wt. % of
 such units. If less than 23 wt. % vinylidene fluoride units are present,
 the polymerization rate is very slow. In addition, good low temperature
 flexibility cannot be achieved. Vinylidene fluoride levels above 65 wt. %
 result in polymers that contain crystalline domains and are characterized
 by poor low temperature compression set resistance and reduced fluids
 resistance.
 Perfluoro(alkyl vinyl) ethers (PAVE) suitable for use as comonomers include
 those of the formula
EQU CF.sub.2.dbd.CFO(R.sub.f' O).sub.n (R.sub.f" O).sub.m R.sub.f (I)
 where R.sub.f' and R.sub.f" are different linear or branched
 perfluoroalkylene groups of 2-6 carbon atoms, m and n are independently
 0-10, and R.sub.f is a perfluoroalkyl group of 1-6 carbon atoms.
 A preferred class of perfluoro(alkyl vinyl) ethers includes compositions of
 the formula
EQU CF.sub.2.dbd.CFO(CF.sub.2 CFXO).sub.n R.sub.f (II)
 where X is F or CF.sub.3, n is 0-5, and R.sub.f is a perfluoroalkyl group
 of 1-6 carbon atoms.
 A most preferred class of perfluoro(alkyl vinyl) ethers includes those
 ethers wherein n is 0 or 1 and R.sub.f contains 1-3 carbon atoms. Examples
 of such perfluorinated ethers include perfluoro(methyl vinyl) ether and
 perfluoro(propyl vinyl) ether. Other useful monomers include compounds of
 the formula
EQU CF.sub.2.dbd.CFO[(CF.sub.2).sub.m CF.sub.2 CFZO].sub.n R.sub.f (III)
 where R.sub.f is a perfluoroalkyl group having 1-6 carbon atoms,
 m=0 or 1, n=0-5, and Z=F or CF.sub.3.
 Preferred members of this class are those in which R.sub.f is C.sub.3
 F.sub.7, m=0, and n=1.
 Additional perfluoro(alkyl vinyl) ether monomers include compounds of the
 formula
EQU CF.sub.2.dbd.CFO[(CF.sub.2 CFCF.sub.3 O).sub.n (CF.sub.2 CF.sub.2 CF.sub.2
 O).sub.m (CF.sub.2).sub.p ]C.sub.x F.sub.2x+1 (IV)
 where m and n independently=1-10, p=0-3, and x=1-5.
 Preferred members of this class include compounds where n=0-1, m=0-1, and
 x=1.
 Examples of useful perfluoro(alkoxy vinyl) ethers include
EQU CF.sub.2.dbd.CFOCF.sub.2 CF(CF.sub.3)O(CF.sub.2 O).sub.m C.sub.n F.sub.2n+1
 (V)
 where n=1-5, m=1-3, and where, preferably, n=1.
 Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl)
 ethers may also be used.
 The perfluoro(alkyl vinyl) ether content of the fluoroelastomers of the
 invention ranges from 25-75 wt. %. If perfluoro(methyl vinyl) ether is
 used, then the fluoroelastomer preferably contains between 30-44 wt. %
 copolymerized perfluoroether units. If less than 25 wt. % perfluoro(alkyl
 vinyl) ether is present, the low temperature properties of the
 fluoroelastomers are adversely affected.
 Copolymerized units of tetrafluoroethylene may also be present in the
 fluoroelastomers of the invention at levels up to 30 wt. %. The presence
 of copolymerized units of TFE is desirable for the purpose of increasing
 fluorine content without unduly compromising low temperature flexibility.
 High fluorine content promotes good fluid resistance. If TFE is present as
 a comonomer, it is preferably copolymerized in amounts of at least 3 wt.
 %. Levels of 3 wt. % or greater TFE lead to improved fluid resistance in
 some end use applications. TFE levels above 30 wt. % result in some
 polymer crystallinity which affects low temperature compression set and
 flexibility.
 The fourth copolymerized monomer unit in the polymers of the invention is
 2-hydropentafluoropropene (HPFP). A particular characteristic of the HPFP
 monomer is that it acts as an independent cure site monomer that takes
 part in crosslinking reactions with polyhydroxylic curing agents. Polymers
 that contain copolymerized HPFP monomer units do not require the presence
 of copolymerized monomer sequences of VF.sub.2 flanked by
 perfluoromonomers (e.g. HFP/VF.sub.2 /HFP) for initiation of
 dehydrofluorination. Introduction of copolymerized HPFP units into the
 VF.sub.2 /HFP copolymer chain creates sites that exceed the reactivity of
 HFP/VF.sub.2 /HFP sequences. HFP is a perfluorinated monomer and thus
 contains no hydrogens. It cannot function as an independent cure site
 monomer because it is incapable of undergoing dehydrofluorination. In
 fact, HFP-containing VF.sub.2 copolymers of PMVE must contain at least
 about 8-10 wt. % HFP in order to provide a sufficient concentration of
 --CF.sub.2 CF(CF.sub.3)CH.sub.2 CF.sub.2 CF.sub.2 -- sequences for
 effective cure by polyhydroxylic compounds.
 HPFP/TFE/PMVE terpolymers are disclosed in U.S. Pat. Nos. 5,478,902 and
 5,719,245. In addition, HPFP/TFE/PMVE tetrapolymers containing not more
 than about 20 mole percent of an additional monomer are disclosed therein.
 Compositions containing high levels of VF.sub.2 comonomer are not
 disclosed. In addition, U.S. Pat. No. 5,874,506 discloses VF.sub.2
 /TFE/HFP/HPFP tetrapolymers. The polymers must contain 16-30 mol % HFP.
 Pentapolymers containing up to 5 mol % of additional comonomers are also
 disclosed therein. The tetrapolymers and pentapolymers disclosed in this
 reference do not exhibit good low temperature properties and have very
 different fluids resistance from the polymers of the present invention.
 Because of the ease of hydrogen abstraction in HPFP-containing VF.sub.2
 fluoroelastomers, the polymers of the present invention require only low
 levels of HPFP, i.e. 0.3-5 wt. %, to promote efficient polyhydroxylic
 cures. This permits adjustment of other comonomer levels to maximize
 particular physical properties. Thus, the polymers of the present
 invention exhibit excellent cure characteristics with only low levels of
 HPFP. They maintain the high temperature compression set resistance
 properties and excellent cure response characteristic of polymers having
 significant amounts of copolymerized VF.sub.2. Further, they exhibit a
 combination of excellent low temperature properties and processability not
 found in prior art fluoroelastomers. Preferably levels of HPFP will be
 between 0.7 and 3.0 wt. %.
 The polymers of this invention may be prepared using free radical batch or
 semi-batch, or continuous free radical emulsion polymerization processes.
 They may also be prepared by free radical suspension polymerization
 processes.
 For example, if a continuous emulsion process is utilized, the polymers are
 generally prepared in a continuous stirred tank reactor. Polymerization
 temperatures may be in the range of 40.degree. to 145.degree. C.,
 preferably 100.degree. to 135.degree. C. at pressures of 2 to 8 MPa.
 Residence times of 20 to 60 minutes are preferred. Free radical generation
 may be effected through use of a water-soluble initiator such as ammonium
 persulfate, either by thermal decomposition or by reaction with a reducing
 agent such as sodium sulfite. An inert surface-active agent such as
 ammonium perfluorooctanoate may be utilized to stabilize the dispersion,
 usually in conjunction with addition of a base such as sodium hydroxide or
 a buffer such as disodium phosphate to control pH in the range 3 to 7.
 Unreacted monomer is removed from the reactor effluent latex by
 vaporization at reduced pressure. Polymer is recovered from the stripped
 latex by coagulation. For example, coagulation may be effected by reducing
 latex pH to about 3 by addition of acid, then adding a salt solution, such
 as an aqueous solution of calcium nitrate, magnesium sulfate, or potassium
 aluminum sulfate, to the acidified latex. The polymer is separated from
 the serum, then washed with water and subsequently dried. After drying,
 the product may be cured.
 Chain transfer agents may be used in the polymerization in order to control
 the molecular weight distribution of the resulting polymers. Examples of
 chain transfer agents include isopropanol; methyl ethyl ketone; ethyl
 acetate; diethyl malonate; isopentane; 1,3-diiodoperfluoropropane;
 1,4-diiodoperfluorobutane; 1,6-diiodoperfluorohexane;
 1,8-diiodoperfluorooctane; methylene iodide; trifluoromethyl iodide;
 perfluoro(isopropyl) iodide; and perfluoro(n-heptyl) iodide.
 Polymerization in the presence of iodine-containing chain transfer agents
 may result in a polymer with one or two iodine atoms per fluoroelastomer
 polymer chain, bound at the chain ends (see for example U.S. Pat. No.
 4,243,770 and U.S. Pat. No. 15 4,361,678). Such polymers may have improved
 flow and processability compared to polymers made in the absence of a
 chain transfer agent. Generally, up to about 1 weight percent iodine
 chemically bound to fluoroelastomer chain ends will be incorporated into
 the polymer, preferably from 0.1-0.3 wt. %.
 Another embodiment of the present invention is a curable composition that
 comprises the above-described copolymers and a polyhydroxylic curing
 agent. The polymers of the invention are also curable with amines and
 amine derivatives, for example carbamates.
 Any of the known polyhydroxylic aromatic crosslinking agents that require
 accelerators for satisfactory cure rates are suitable for use with the
 fluoroelastomers of the present invention. The crosslinking agent is
 usually added in amounts of from about 0.5-4 parts by weight per hundred
 parts by weight fluoroelastomer (phr), usually 1-2.5 phr. Preferred
 crosslinking agents are di- tri-, tetrahydroxybenzenes, naphthalenes,
 anthracenes and bisphenols of the formula
 ##STR1##
 where A is a stable divalent radical, such as a difunctional aliphatic,
 cycloaliphatic, or aromatic radical of 1-13 carbon atoms, or a thio, oxy,
 carbonyl, sulfinyl, or sulfonyl radical; A is optionally substituted with
 at least one chlorine or fluorine atom; x is 0 or 1; n is 1 or 2 and any
 aromatic ring of the polyhydroxylic compound is optionally substituted
 with at least one atom of chlorine, fluorine, or bromine, a --CHO group,
 or a carboxyl or acyl radical (e.g. a --COR where R is OH or a C.sub.1
 -C.sub.8 alkyl, aryl, or cycloalkyl group). It will be understood from the
 above formula describing bisphenols that the --OH groups can be attached
 in any position (other than number one) in either ring. Blends of two or
 more such compounds can also be used.
 Referring to the bisphenol formula shown in the previous paragraph, when A
 is alkylene, it can be, for example, methylene, ethylene, chloroethylene,
 fluoroethylene, difluoroethylene, 1,3-propylene, 1,2-propylene,
 tetramethylene, chlorotetramethylene, fluorotetramethylene,
 trifluorotetramethylene, 2-methyl-1,3-propylene, 2-methyl-1,2-propylene,
 pentamethylene, and hexamethylene. When A is alkylidene, it can be for
 example ethylidene, dichloroethylidene, difluoroethylidene, propylidene,
 isopropylidene, trifluoroisopropylidene, hexafluoroisopropylidene,
 butylidene, heptachlorobutylidene, heptafluorobutylidene, pentylidene,
 hexylidene, and 1,1-cyclohexylidene. When A is a cycloalkylene radical, it
 can be for example 1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene,
 2-fluoro-1,4-cyclohexylene, 1,3-cyclohexylene, cyclopentylene,
 chlorocyclopentylene, fluorocyclopentylene, and cycloheptylene. Further, A
 can be an arylene radical such as m-phenylene, p-phenylene,
 2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene, o-phenylene,
 methylphenylene, dimethylphenylene, trimethylphenylene,
 tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene,
 5-chloro-1,4-naphthylene, 1,5-naphthylene, and 2,6-naphthylene.
 Other useful crosslinking agents include hydroquinone, dihydroxybenzenes
 such as catechol, resorcinol, 2-methyl resorcinol, 5-methyl resorcinol,
 2-methyl hydroquinone, 2,5-dimethyl hydroquinone; 2-t-butyl hydroquinone;
 and 1,5-dihydroxynaphthalene.
 Additional polyhydroxy curing agents include alkali metal salts of
 bisphenol anions, quaternary ammonium salts of bisphenol anions and
 quaternary phosphonium salts of bisphenol anions. For example, the salts
 of bisphenol A and bisphenol AF. Specific examples include the disodium
 salt of bisphenol AF, the dipotassium salt of bisphenol AF, the monosodium
 monopotassium salt of bisphenol AF and the benzyltriphenylphosphonium salt
 of bisphenol AF. Quaternary ammonium and phosphonium salts of bisphenol
 anions and their preparation are discussed in U.S. Pat. Nos. 4,957,975 and
 5,648,429.
 In addition, derivatized polyhydroxy compounds, such as diesters, are
 useful crosslinking agents. Examples of such compositions include diesters
 of phenols, such as the diacetate of bisphenol AF, the diacetate of
 sulfonyl diphenol, and the diacetate of hydroquinone.
 When cured with polyhydroxy compounds, the curable compositions will also
 generally include a cure accelerator. The most useful accelerators are
 quaternary phosphonium salts, quaternary alkylammonium salts, or tertiary
 sulfonium salts. Particularly preferred accelerators are
 n-tetrabutylammonium hydrogen sulfate, tributylallylphosphonium chloride
 and benzyltriphenylphosphonium chloride. Other useful accelerators include
 those described in U.S. Pat. Nos. 5,591,804; 4,912,171; 4,882,390;
 4,259,463 and 4,250,278 such as tributylbenzylammonium chloride,
 tetrabutylammonium bromide, tetrabutylammonium chloride, benzyl
 tris(dimethylamino)phosphonium chloride;
 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenonium chloride, [(C.sub.6
 H.sub.5).sub.2 S.sup.+ (C.sub.6 H.sub.13)][Cl].sup.-, and [(C.sub.6
 H.sub.13).sub.2 S(C.sub.6 H.sub.5)].sup.+ [CH.sub.3 CO.sub.2 ].sup.-. In
 general, about 0.2 phr accelerator is an effective amount, and preferably
 about 0.35-1.5 phr is used.
 If quaternary ammonium or phosphonium salts of bisphenols are used as
 curing agents, then addition of a cure accelerator is not necessary.
 The polyhydroxy cure system will also contain a metal compound composed of
 a divalent metal oxide, such as magnesium oxide, zinc oxide, calcium
 oxide, or lead oxide, or a divalent metal hydroxide; or a mixture of the
 oxide and/or hydroxide with a metal salt of a weak acid, for example a
 mixture containing about 1-70 percent by weight of the metal salt. Among
 the useful metal salts of weak acids are barium, sodium, potassium, lead,
 and calcium stearates, benzoates, carbonates, oxalates, and phosphites.
 The amount of the metal compound added is generally about 1-15 phr, about
 2-10 parts being preferred.
 Diamines and diamine carbamates are also useful curing agents for the
 compositions of the invention. Examples of useful diamines include
 N,N'-dicinnamylidene-1,6-hexanediamine, trimethylenediamine, cinnamylidene
 trimethylenediamine, cinnamylidene ethylenediamine, and cinnamylidene
 hexamethylenediamine. Examples of useful carbamates are
 hexamethylenediamine carbamate, bis(4-aminocyclohexyl)methane carbamate,
 1,3-diaminopropane monocarbamate, ethylenediamine carbamate and
 trimethylenediamine carbamate. Usually about 0.1-5 phr of the carbamate is
 used.
 Other additives may be compounded into the fluoroelastomer to optimize
 various physical properties. Such additives include carbon black,
 stabilizers, plasticizers, lubricants, pigments, fillers, and processing
 aids typically utilized in perfluoroelastomer compounding. Any of these
 additives can be incorporated into the compositions of the present
 invention, provided the additive has adequate stability for the intended
 service conditions.
 Carbon black is used in elastomers as a means to balance modulus, tensile
 strength, elongation, hardness, abrasion resistance, conductivity, and
 processability of the compositions. Carbon black is generally useful in
 amounts of from 5-60 phr.
 In addition, or in the alternative, fluoropolymer fillers may be present in
 the composition. Generally from 1 to 50 phr of a fluoropolymer filler is
 used, and preferably at least about 5 phr is present. The fluoropolymer
 filler can be any finely divided, easily dispersed plastic fluoropolymer
 that is solid at the highest temperature utilized in fabrication and
 curing of the perfluoroelastomer composition. By solid, it is meant that
 the fluoroplastic, if partially crystalline, will have a crystalline
 melting temperature above the processing temperature(s) of the
 perfluoroelastomer(s). Such finely divided, easily dispersed
 fluoroplastics are commonly called micropowders or fluoroadditives.
 Micropowders are ordinarily partially crystalline polymers.
 A preferred additive class includes molecular sieves, particularly
 zeolites. Molecular sieve zeolites are crystalline aluminosilicates of
 Group IA and Group IIA elements, such as sodium, potassium, magnesium, and
 calcium. Chemically, they are represented by the empirical formula:
 M.sub.2/n O.Al.sub.2 O.sub.3.ySiO.sub.2.wH.sub.2 O where y is 2 or
 greater, n is the cation valence, and w represents the water contained in
 the voids of the zeolite. Commercially available examples of such
 compositions include Molecular Sieve 3A, Molecular Sieve 4A, Molecular
 Sieve 5A, and Molecular Sieve 13X, all available from Aldrich Chemical
 Co., Inc. Milwaukee, Wis. Use of this class of additives prevents sponging
 and improves heat aging of vulcanizates upon press curing in many
 instances. In general, use of about 1-5 phr is sufficient.
 Other preferred additives include modified silane coated mineral fillers.
 By "modified silane" is meant that the silane contains at least one
 reactive functional group such as an amino group, or an epoxy group. The
 mineral fillers used in this invention are preferably somewhat alkaline,
 such as calcium metasilicates (CaSiO.sub.3), especially wollastonite.
 Wollastonite coated with either an aminosilane or an epoxysilane is
 especially preferred. These compounds are commercially available from
 Quartzwerke GmbH of Freschen, Germany as Tremin.RTM.283 EST (epoxysilane
 treated wollastonite) and Tremin.RTM.283 AST (aminosilane treated
 wollastonite). These modified silane coated mineral fillers prevent
 sponging of the fluoroelastomer composition during press cure and also
 accelerate the cure rate. Generally, about 5 to 80 phr modified silane
 coated mineral filler is useful in the compositions of this invention,
 about 10 to 60 phr being preferred.
 Organotin hydrides are another class of additive that may be employed.
 Tri-n-butyltin hydride (TBTH) is especially preferred. These tin hydride
 fillers accelerate the cure rate of the compositions of this invention and
 increase the modulus and improve the compression set resistance of the
 cured compounds. Generally, about 0.2 to 1.5 phr organotin hydride filler
 is useful, about 0.4 to 0.8 phr being preferred.
 The crosslinking agent, accelerator, metal oxide, and other additives are
 generally incorporated into the polymer by means of an internal mixer or
 on a rubber mill. The resultant composition is then cured, generally by
 means of heat and pressure, for example by compression transfer or
 injection molding.
 The curable compositions of the present invention are useful in production
 of gaskets, tubing, seals and other molded components. Such articles are
 generally produced by molding a compounded formulation of the curable
 composition with various additives under pressure, curing the part, and
 then subjecting it to a post cure cycle. The cured compositions have
 excellent low temperature flexibility and processability as well as
 excellent thermal stability and chemical resistance. They are particularly
 useful in applications such as seals and gaskets requiring a good
 combination of oil resistance, fuel resistance and low temperature
 flexibility, for example in fuel injection systems, fuel line connector
 systems and in other seals for high and low temperature automotive uses.
 The invention is now illustrated by certain embodiments wherein all parts
 and percentages are by weight unless otherwise specified.

EXAMPLES
 Test Methods
 Cure Characteristics
 Unless otherwise noted, cure characteristics were measured using a Monsanto
 oscillating disk rheometer (ODR), under conditions corresponding to ASTM D
 2084 at 1.degree. arc, 24 minutes, 180.degree. C. The following cure
 parameters were recorded:
 M.sub.H : maximum torque level, in units of dN.multidot.m
 M.sub.L : minimum torque level, in units of dN.multidot.m
 Delta M: difference between maximum and minimum torque, in units of
 dN.multidot.m
 t.sub.s 2: minutes to a 2.26 dNm rise above M.sub.L
 tc50: minutes to 50% of maximum torque
 tc90: minutes to 90% of maximum torque
 Tensile Properties
 Unless otherwise noted, stress/strain properties were measured on test
 specimens that had been press cured at 180.degree. C. for 15 minutes and
 then post cured in a hot air oven for 24 hours at 232.degree. C. The
 following physical property parameters were recorded; test methods are in
 parentheses:
 M.sub.100 : modulus at 100% elongation in units of MPa (ISO 37)
 T.sub.B : tensile strength in units of MPa (ISO 37)
 T.sub.S : tear strength in units of dN/m (ISO 34, Die B)
 E.sub.B : elongation at break in units of % (ISO 37)
 TR-10: temperature of retraction (ISO 2921)
 According to the TR test method, a standard test piece of length 50 mm is
 stretched at room temperature and then cooled in a bath (usually filled
 with isopropanol) to a temperature of about 10.degree. C. less than the
 T.sub.g of the polymer. The test piece is then allowed to retract freely
 while the test temperature is raised at a rate of 1.degree. C. per minute.
 Readings of the retracted length are taken every 2 minutes until the
 retraction reaches 75%. TR-10 is the temperature at which a retraction of
 10% is achieved.
 Hardness (Shore A, ISO 868)
 Compression set of small pip samples (ISO 815)
 Example 1
 A polymer of the invention, Polymer 1A, was prepared by continuous emulsion
 polymerization, carried out at 120.degree. C. in a well-stirred 2.0 liter
 stainless steel liquid full reaction vessel. An aqueous solution,
 consisting of 2.68 g/hour (g/h) ammonium persulfate, 1.4 g/h sodium
 hydroxide, 3.4 g/h ammonium perfluorooctanoate, and 0.7 g/h isopropanol in
 deionized water, was fed to the reactor at a rate of 4 L/hour. The reactor
 was maintained at a liquid-full level at a pressure of 6.2 MPa by means of
 a back-pressure control valve in the effluent line. After 30 minutes,
 polymerization was initiated by introduction of a gaseous monomer mixture
 consisting of 113.1 g/h tetrafluoroethylene (TFE), 614.1 g/h vinylidene
 fluoride (VF.sub.2), and 391.2 g/h perfluoro(methylvinyl) ether (PMVE) fed
 through a diaphragm compressor. After 15 minutes more,
 2-hydropentafluoropropylene (HPFP) was added to the remainder of the
 gaseous mixture and added at a rate of 32.9 g/h. After 1.5 hours, effluent
 dispersion was collected for 6 hours. The effluent polymer dispersion,
 which had a pH of 4.5 and contained 22.0 wt. % solids, was separated from
 residual monomers in a degassing vessel at atmospheric pressure.
 Fluoroelastomer product was isolated from the dispersion by reducing the
 pH to about 3 with dilute nitric acid and coagulating with calcium nitrate
 solution. The coagulated polymer was allowed to settle, supernatant serum
 was removed, and the polymer was washed by reslurrying in water twice
 before filtering. The wet crumb was dried in an air oven at approximately
 50.degree.-65.degree. C. to a moisture content of less than 1%. About 6.7
 kg of polymer was recovered at an overall conversion of 97%. The product,
 composed of 10.09 wt. % TFE units, 53.96 wt. % VF.sub.2 units, 34.05 wt. %
 PMVE units and 1.9 wt. % HPFP units, was an amorphous elastomer having a
 glass transition temperature of -28.degree. C., as determined by
 differential scanning calorimetry (heating mode, 10.degree. C./minute,
 inflection point of transition). Inherent viscosity of the elastomer was
 0.87 dL/g, measured at 30.degree. C. in methyl ethyl ketone, and Mooney
 viscosity, ML-10 (121.degree. C.), was 49.
 A second polymer of the invention, Polymer 1B, was prepared in
 substantially the same manner. An aqueous solution, consisting of 2.64 g/h
 APS, 1.2 g/h sodium hydroxide, and 2.2 g/h ammonium perfluorooctanoate in
 deionized water, was fed to the reactor at a rate of 4 L/h. After 30
 minutes, polymerization was initiated by introducing a gaseous monomer
 mixture consisting of 113.1 g/h TFE, 614.1 g/h VF.sub.2, and 391.2 g/h
 PMVE fed through a diaphragm compressor. After 15 minutes more, HPFP was
 added to the remainder of the gaseous mixture and was fed to the reactor
 at a rate of 32.9 g/h. After 1.5 hours, effluent dispersion was collected
 for 2.5 hours. The effluent polymer dispersion, having a pH of 4.0 and
 containing 21.7% solids, was separated from residual monomers.
 Fluoroelastomer product was isolated from the dispersion by reducing the
 pH to about 3 with dilute sulfuric acid and coagulating with potassium
 aluminum sulfate solution. The coagulated polymer was treated as described
 for Polymer 1A and wet crumb was dried in an air oven at approximately
 50-65.degree. C. to a moisture content of less than 1%. About 2.8 kg of
 polymer was recovered at an overall conversion of 98%. The polymer
 product, composed of 9.99 wt. % TFE units, 54.12 wt. % VF.sub.2 units,
 33.85 wt. % PMVE units and 2.04 wt. % HPFP units, was an amorphous
 elastomer having a glass transition temperature of -29.degree. C., as
 determined by differential scanning calorimetry (heating mode, 10.degree.
 C./minute, inflection point of transition). Inherent viscosity of the
 elastomer was 1.10 dL/g, measured at 30.degree. C. in methyl ethyl ketone,
 and Mooney viscosity, ML-10 (121.degree. C.), was 89.
 A third polymer, Control Polymer A, was prepared generally according to the
 process disclosed in U.S. Pat. No. 4,214,060. It differed from Polymers 1A
 and 1B in that the cure site monomer 4-bromo-3,3,4,4-tetrafluorobutene-1
 (BTFB) was used in place of HPFP. The copolymer was composed of 55 wt. %
 VF.sub.2 units, 10 wt. % TFE units, 34.8 wt. % PMVE units and 1.2 wt. %
 BTFB units.
 Samples of Polymer 1A, Polymer 1B, and Control Polymer A were compounded on
 a two-roll rubber mill with the components shown in Table I. Cure
 characteristics and physical properties of the cured compositions,
 measured according to the Test Methods described above, are also reported
 in Table I.
 The physical properties of Samples 1A-1D compared favorably to those of the
 Control polymer, which has desirable physical properties and good low
 temperature sealing performance. In addition, Samples 1A-1D were much
 easier to demold than the Control.
 TABLE I
 Sample 1 Sample 2 Sample 3 Sample 4 Control
 Formulation
 Polymer 1A 100 100
 Polymer 1B 100 100
 Control Polymer A 100
 MT Carbon Black.sup.1 30 30 30 30 30
 Calcium Oxide VG 6 6 6 6
 Calcium Hydroxide 5
 Molecular sieve 13X 3 3 3 3
 VPA No. 2.sup.2 0.5 0.5 0.5 0.5 0.5
 Luperox 101 XL.sup.3 4
 Diak #8.sup.4 2
 TBAHS.sup.5 0.5 0.6 0.5 0.6
 Bisphenol AF.sup.6 2.5 3 2.5 3
 Cure Characteristics
 M.sub.L, dNm 4.32 4.09 7.14 6.92 10.26
 M.sub.H, dNm 45.6 50.75 43.86 55.54 56.84
 Delta M, dNm 41.28 46.66 36.72 48.62 46.6
 t.sub.S 2 2.72 2.77 3.22 3.37 1.8
 tc50, minutes 5.37 6.13 7.26 7.9 3.72
 tc90, minutes 12.49 11.8 18.04 16.15 7.16
 Stress Strain
 Properties
 T.sub.B, MPa 12.8 12.4 15.1 15.3 20.1
 E.sub.B, % 254 219 244 230 212
 M.sub.100, MPa 4.5 4.7 5 5.3 6.1
 TS, kN/m 22.5 22.4 20.1 21.8 20.9
 Hardness (Shore A) 71.5 73.1 70.7 72.3 68.7
 TR-10, .degree. C. -26 -26 -28
 Compression Set
 @200.degree. C., 70 hours, % 37.5 38.8 32 35
 26.2
 .sup.1 Thermax FF N 990 medium thermal carbon black (available from Lehmann
 & Voss Co.)
 .sup.2 Rice Bran Wax (available from DuPont Dow Elastomers L.L.C.)
 .sup.3 2,5-Dimethyl-2,5-di(t-butylperoxy)hexane, 45% Active (available from
 Atochem)
 .sup.4 Trimethylallylisocyanurate (available from DuPont Dow Elastomers
 L.L.C.)
 .sup.5 Tetrabutylammonium hydrogen sulfate (available from DuPont Dow
 Elastomers L.L.C.)
 .sup.6 4,4'(Hexafluoroisopropylidene)diphenol (available from DuPont Dow
 Elastomers L.L.C.)
 Example 2
 Polymer 2, a polymer of the invention, was prepared by continuous emulsion
 polymerization carried out at 110.degree. C. in a well-stirred 4.0 liter
 stainless steel reaction vessel, substantially according to the procedure
 described for preparation of Polymer 1A. An aqueous solution consisting of
 6.47 g/h ammonium persulfate, 3.6 g/h sodium hydroxide, and 5.5 g,/h
 ammonium perfluorooctanoate, in deionized water was fed to the reactor at
 a rate of 8 L/h. After 30 minutes, the reaction was initiated by
 introducing a gaseous monomer mixture consisting of 524.0 g/h TFE, 748.9
 g/h VF.sub.2, 888.9 g/h PMVE, and 60.4 g/h HPFP fed through a diaphragm
 compressor. After 2 hours, effluent dispersion was collected for 4 hours.
 The effluent polymer dispersion, having a pH of 4.5 and containing 20.9
 wt. % solids was separated from residual monomers. Fluoroelastomer was
 isolated from the dispersion by reducing pH to about 3 with dilute
 sulfuric acid and coagulating with potassium aluminum sulfate solution.
 The coagulated polymer was collected as described in Example 1. The wet
 crumb was dried in an air oven at approximately 50-65.degree. C. to a
 moisture content of less than 1%. About 8.4 kg of polymer was recovered at
 an overall conversion of 95%. The polymer, composed of 24.51 wt. % TFE
 units, 35.14 wt. % VF.sub.2 units, 39.20 wt. % PMVE units and 1.15 wt. %
 HPFP units, was an amorphous elastomer having a glass transition of
 -24.degree. C. as determined by differential scanning calorimetry (heating
 mode, 10.degree. C. /min, inflection point of transition). Inherent
 viscosity of the fluoroelastomer was 0.71 dL/g, measured at 30.degree. C.
 in methyl ethyl ketone, and Mooney viscosity, ML-10 (121.degree. C.), was
 104.
 Control Polymer B was prepared in substantially the same manner as Polymer
 1A. An aqueous solution, consisting of 2.77 g/h ammonium persulfate, 0.80
 g/h sodium hydroxide, and 2.25 g/h ammonium perfluorooctanoate, in
 deionized water, was fed to the reactor at a rate of 4 L/h. After 30
 minutes, the reaction was initiated by introducing a gaseous monomer
 mixture consisting of 320.6 glh TFE, 389.5 g/h VF.sub.2, and 477.4 g/h
 PMVE. After 1.5 hours, effluent dispersion was collected for 7 hours. The
 effluent polymer dispersion, when separated from residual monomers had a
 pH of 3.2 and contained 22.6 weight percent solids. The fluoroelastomer
 was isolated by coagulation as described for Polymer 1A. The wet crumb was
 dried in an air oven at approximately 50-65.degree. C. to a moisture
 content of less than 1%. About 7.9 kg of polymer was recovered at an
 overall conversion of 98%. The polymer, composed of 27.29 wt% TFE units,
 33.30 wt. % VF.sub.2 units, and 39.41 wt. % PMVE. units had an inherent
 viscosity was 0.88 dL/g, measured at 30.degree. C. in methyl ethyl ketone,
 and Mooney viscosity, ML-10 (121.degree. C.) of 100.
 Samples of Polymer 2 and Control Polymer B were compounded with the
 components shown in Table II. Cure characteristics were measured by ODR.
 Control B, which contained no copolymerized HPFP, exhibited essentially no
 cure response.
 TABLE II
 Formulation (parts by weight) Sample 2 Control Sample B
 Polymer 2 100 0
 Control Polymer B 0 100
 MT Carbon Black.sup.1 10 10
 TBAHS.sup.2 1 1
 Bisphenol AF.sup.3 2 2
 MgO 2 2
 Ca(OH).sub.2 2 2
 Cure Characteristics
 M.sub.H, dNm 49.7 --
 delta M, dN.m 39.5 0.6
 t.sub.s 2, minutes 2.7 --
 tc90, minutes 9.7 --
 .sup.1 Thermax FF N 990 medium thermal carbon black (available from Lehmann
 & Voss Co.)
 .sup.2 Tetrabutylammonium hydrogen sulfate (available from DuPont Dow
 Elastomers L.L.C.)
 .sup.3 4,4'(Hexafluoroisopropylidene)diphenol (available from DuPont Dow
 Elastomers L.L.C.)
 Example 3
 Polymer 3, a polymer of the invention, was prepared by semi-batch emulsion
 polymerization carried out at 80.degree. C. in a well-stirred reaction
 vessel. A 33 liter, horizontally agitated reactor was charged with 24.0
 liters of deionized, deoxygenated water and 55.0 g ammonium
 perfluorooctanoate. The reactor was heated to 80.degree. C. and then
 pressurized to 1.5 MPa with a mixture of 10.0 wt. % TFE, 20.0 wt. %
 VF.sub.2, 35.0 wt. % PMVE, and 35 wt. % HPFP. A 40.0 ml sample of a 1%
 ammonium persulfate/3% disodium hydrogen phosphate initiator solution was
 then added. A mixture of 55.0 wt. % VF.sub.2, 33.0 wt. % PMVE, 10.0 wt. %
 TFE, and 2.0 wt. % HPFP was supplied to the reactor to maintain a pressure
 of 1.5 MPa throughout the polymerization. After 300 g of monomer mixture
 had been supplied to the reactor, 13.6 ml of 1,4 diiodoperfluorobutane was
 fed to the reactor over one hour. After the diiodo addition was complete,
 initiator was added at a rate sufficient to maintain 500 g/hour monomer
 consumption. After a total of 8172 g monomer mixture was supplied to the
 reactor, requiring 121 ml initiator solution, monomer addition was
 discontinued and the reactor purged of residual monomer. The resulting
 emulsion was coagulated by addition of sulfuric acid and potassium alum,
 and washed with deionized water. The polymer crumb was dried for two days
 at 60.degree. C. Polymer 3, composed of 52.79 wt. % VF.sub.2 units, 14.80
 wt. % TFE units, 30.57 wt. % PMVE units, 1.67 wt. % HPFP units and 0.17
 wt. % I, had a Mooney viscosity, ML-10 (121.degree. C.), of 51. A sample
 of Polymer 3 was compounded with the components shown in Table III. Curing
 characteristics and physical properties of the cured composition were
 measured according to the Test Methods, except an Alpha Technologies MDR
 was used to measure cure characteristics at a temperature of 180.degree.
 C. and rotor amplitude of 0.5.degree., and physical properties were
 measured on slabs of this composition which had been press cured at
 170.degree. C. for 4 minutes and then post-cured in an air oven at
 230.degree. C. for 24 hours. Results are reported in Table III.
 TABLE III
 Sample 3
 Formulation (phr)
 Polymer 3 100
 Tremin .RTM. 283 600 EST.sup.1 45.0
 MT Carbon Black.sup.2 2.5
 Calcium Oxide 6.0
 Elastomag .RTM. 170.sup.3 1.0
 Molecular sieve 13x 3.0
 Bisphenol AF.sup.4 2.0
 TBAHS.sup.5 0.5
 VPA No.2.sup.6 1.0
 Cure Characteristics
 M.sub.L, dNm 2.35
 M.sub.H, dNm 26.47
 t.sub.s 2, minutes 0.33
 tc90, minutes 1.81
 Stress Strain Properties
 T.sub.B, MPa 12.9
 E.sub.B, % 157
 M.sub.100 MPa 9.6
 Hardness (Shore A) 77.1
 Compression Set
 @200.degree. C., 70 hours, % 36.4
 .sup.1 Calcium meta-silicate treated with aminosilane (available from
 Quartzwerke GmbH Freschen, Germany)
 .sup.2 Thermax FF N 990 medium thermal carbon black (available from Lehmann
 & Voss Co.)
 .sup.3 Magnesium oxide (available from Morton Performance Chemicals, Inc.).
 .sup.4 4,4'(Hexafluoroisopropylidene)diphenol (available from DuPont Dow
 Elastomers L.L.C.)
 .sup.5 Tetrabutylammonium hydrogen sulfate (available from DuPont Dow
 Elastomers L.L.C.)
 .sup.6 Rice Bran Wax (available from DuPont Dow Elastomers L.L.C.)
 Example 4
 Polymer 4, a polymer of the invention, was prepared by continuous emulsion
 polymerization in a well-stirred stainless steel liquid full reaction
 vessel. The reactor was heated to 125.degree. C. and the aqueous solution
 was fed at 4 L/h. The aqueous feed consisted of 1.58 g/h ammonium
 persulfate (APS), 1.2 g/h sodium hydroxide, and 2.2 g/h ammonium
 perfluorooctanoate (FC-143) and 0.47 g/h isopropanol in deionized water.
 The reactor was kept liquid-full at 6.2 MPa by means of a back-pressure
 control valve in the effluent line. After 30 minutes, the reaction was
 started by introducing a gaseous monomer mixture consisting of 88.2 g/h
 tetrafluoroethylene (TFE), 614.1 g/h vinylidene fluoride (VF.sub.2), and
 413.8 g/h perfluoromethylvinyl ether (PMVE) fed through a diaphragm
 compressor. After 15 minutes, another gaseous monomer was added to the
 rest of the gaseous mixture, 35.2 g/h 2-hydropentafluoro-propylene (HPFP).
 After 1.5 hours, effluent dispersion was collected for 5 hours.
 The effluent polymer dispersion was separated from residual monomers in a
 degassing vessel at atmospheric pressure. The dispersion had a pH of 4.6
 and contained 21.4 weight percent solids. The fluoroelastomer was isolated
 from the dispersion by reducing pH to about 3 with dilute sulfuric acid
 and coagulating with potassium aluminum sulfate solution. The coagulated
 polymer was allowed to settle, supernatant serum was removed, and the
 polymer was washed by reslurrying in the water twice before filtering. The
 wet crumb was dried in an air oven at approximately 50.degree.-65.degree.
 C. to a moisture content of less than 1%.
 Polymer product was recovered at an overall conversion of 97%. The polymer
 had the composition of 7.8 wt. % TFE, 54.29 wt. % VF.sub.2, 35.98 wt. %
 PMVE and 1.93 wt. % HPFP. The polymer was an amorphous elastomer with a
 glass transition of -29.degree. C. as determined by differential scanning
 calorimetry (heating mode, 10.degree. C. /minute, inflection point of
 transition). Fluoroelastomer inherent viscosity was 1.14 dL/g, measured at
 30.degree. C. in methyl ethyl ketone, and Mooney viscosity was measured as
 ML-10 (121.degree. C.)=82.
 Polymer 4 was compounded on a two-roll rubber mill with the additives shown
 in Table IV. Curing characteristics, measured in accordance with the Test
 Methods (except 1.degree. arc, 180.degree. C., 12 minutes), are also shown
 in Table IV. Sample 4A, containing tri-n-butyltin hydride, exhibited a
 much faster cure rate (70.5 dNm/minute) than Sample 4B, which did not
 contain tin hydride.
 TABLE IV
 Sample 4A Sample 4B
 Formulation (phr)
 Polymer 4 100 100
 MT Carbon Black.sup.1 30 30
 Elastomag 170.sup.2 3 3
 Calcium Oxide VG 6 6
 Moecular sieve 13x 3 3
 VC50.sup.3 2.5 2.5
 VPA No. 2.sup.4 1.0 0
 Tri-n-butyltin hydride 0 1.0
 Cure Characteristics
 ML, dNm 11.5 12.2
 MH, dNm 54.6 55.7
 Delta M, dNm 43.1 43.5
 t.sub.s 2, minutes 1.56 1.10
 tc50, minutes 2.51 1.58
 tc90, minutes 3.87 2.39
 Peak Rate, dNm/minute 39 70.5
 .sup.1 Thermax FF N 990 medium thermal carbon black (available from Lehmann
 & Voss Co.)
 .sup.2 Magnesium oxide (available from Morton Performance Chemicals, Inc.).
 .sup.3 An 80 wt. %/20 wt. % salt of bisphenol AF reacted with
 benzyltriphenylphosphonium chloride (available ftom DuPont Dow Elastomers
 L.L.C.)
 .sup.4 Rice Bran Wax (available from DuPont Dow Elastomers L.L.C.)
 Example 5
 Polymer 5, a polymer of the invention, was prepared by emulsion
 polymerization. A continuous emulsion polymerization was carried out in a
 well-stirred stainless steel liquid full reaction vessel. The reactor was
 heated to 110.degree. C. and the aqueous solution was fed at 3 L/h. The
 aqueous feed consisted of 1.27 g/hour (g/h) ammonium persulfate (APS),
 0.91 g/h sodium hydroxide, 1.7 g/h ammonium perfluorooctanoate (FC-143),
 and 0.35 g/h isopropanol in deionized water. The reactor was kept
 liquid-full at 6.2 MPa by means of a back-pressure control valve in the
 effluent line. After 30 minutes, the reaction was started by introducing a
 gaseous monomer mixture consisting of 61.2 g/h tetrafluoroethylene (TFE),
 462.4 g/h vinylidene fluoride (VF.sub.2), and 321.7 g/h
 perfluoro(methylvinyl) ether (PMVE) fed through a diaphragm compressor.
 After 15 minutes, another gaseous monomer was added to the rest of the
 gaseous mixture, 27.0 g/h 2-hydropentafluoropropylene (HPFP). After 1.5
 hours, effluent dispersion was collected for 6 hours.
 The effluent polymer dispersion was separated from residual monomers in a
 degassing vessel at atmospheric pressure. The dispersion had a pH of 5.8
 and contained 21.4 weight percent solids. The fluoroelastomer was isolated
 from the dispersion by reducing pH to about 3 with dilute nitric acid and
 coagulating with calcium nitrate solution. The coagulated polymer was
 allowed to settle, supernatant serum was removed, and the polymer was
 washed by reslurrying in the water twice before filtering. The wet crumb
 was dried in an air oven at approximately 50.degree.-65.degree. C. to a
 moisture content of less than 1%.
 Polymer product was recovered at an overall conversion of 97%. The polymer
 had a copolymerized monomer composition of 7.16 wt. % TFE, 54.06 wt. %
 VF.sub.2, 36.85 wt. % PMVE and 1.9 wt. % HPFP. The polymer was an
 amorphous elastomer with a glass transition temperature of -28.degree. C.
 as determined by differential scanning calorimetry (heating mode,
 10.degree. C./minute, inflection point of transition). Fluoroelastomer
 inherent viscosity was 1.22 dL/g, measured at 30.degree. C. in methyl
 ethyl ketone, and Mooney viscosity was measured as ML-10 (121.degree.
 C.)=98.
 Polymer 5 was compounded on a two-roll rubber mill with the additives shown
 in Table V. Curing characteristics and physical properties of the cured
 compositions were measured according to the Test Methods and are also
 reported in Table V.
 TABLE V
 5A 5B 5C 5D 5E 5F 5G
 Formulation, phr
 Polymer 5 100 100 100 100 100 100
 100
 MT Carbon Black.sup.1 2.5 2.5 2.5 2.5 2.5 2.5
 2.5
 Tremin .RTM. 283 400 EST.sup.2 45 0 0 0 0
 0 0
 Tremin .RTM. 283 600 EST.sup.3 0 45 0 0 0
 0 0
 Tremin .RTM. 283 600 AST.sup.4 0 0 45 0 0
 0 0
 Tremin .RTM. 283 EST 800M.sup.5 0 0 0 45 0
 0 0
 Tremin .RTM. 283 800 TST.sup.6 0 0 0 0 45
 0 0
 Nyad .RTM. 400.sup.7 0 0 0 0 0 45 0
 Blanc Fixe Micro.sup.8 0 0 0 0 0 0
 70
 Calcium Oxide VG 6 6 6 6 6 6 6
 Elastomag .RTM. 170.sup.9 1 1 1 1 1 1
 1
 Molecular sieves 13x 3 3 3 3 3 3 3
 Bisphenol AF.sup.10 2 2 2 2 2 2 2
 TBAHS.sup.11 0.5 0.5 0.5 0.5 0.5 0.5
 0.5
 VPA No. 2.sup.12 1 1 1 1 1 1 1
 Cure Characteristics
 ML, dNm 3.26 3.07 3.47 3.65 3.71 2.64
 3.06
 MH, dNm 22.9 24.5 23.6 24.4 24.6 21.1
 22.1
 Delta M, dNm 19.6 21.4 20.1 20.7 20.9 18.5
 19.0
 t.sub.S 2, minutes 0.55 0.48 0.58 0.53 0.48 0.94
 1.17
 tc50, minutes 0.79 0.66 0.8 0.72 0.65 1.44
 2.45
 tc90, minutes 1.95 2.01 2.2 2.38 2.79 2.75
 7.55
 Peak rate, dNm/minute 42.7 58.9 45.9 54.7 58.4 22.5
 6.8
 Stress Strain Properties
 T.sub.B, MPa 12.6 14.1 14.2 15.6 10.1
 1.4
 E.sub.B, % 177.6 178 173 169 196
 210
 M.sub.100, MPa 8.7 8.8 9.4 9.7 7.3
 5.8
 Hardness (Shore A) 73.7 73.9 74.1 74.9 72.1
 73.9
 Compression Set
 @200.degree. C., 70 hours, % 32.7 30.1 30.7 30.4 38.9
 36.9
 Sponging No No No No Yes No No
 .sup.1 Thermax FF N 990 medium thermal carbon black (available from Lehmann
 & Voss Co.)
 .sup.2 Epoxysilane coated wollastonite
 .sup.3 Epoxysilane coated wollastonite
 .sup.4 Aminosilane coated wollastonite
 .sup.5 Epoxysilane coated wollastonite
 .sup.6 Methylsilane coated wollastonite
 .sup.7 Non-coated wollastonite
 .sup.8 Precipitated BaSO.sub.4
 .sup.9 Magnesium oxide (available from Morton Performance Chemicals, Inc.).
 .sup.10 4,4'(Hexafluoroisopropylidene)diphenol (available from DuPont Dow
 Elastomers L.L.C.)
 .sup.11 Tetrabutylammonium hydrogen sulfate (available from DuPont Dow
 Elastomers L.L.C.)
 .sup.12 Rice Bran Wax (available from DuPont Dow Elastomers L.L.C.)