Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
  • C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08L27/18—Homopolymers or copolymers or tetrafluoroethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/14—Treatment of polymer emulsions
  • C08F6/22—Coagulation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
  • C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
  • C08J3/075—Macromolecular gels
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
  • C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group

Definitions

• the present invention relates to perfluoroelastomeric compositions having an improved thermal resistance, improved sealing properties, improved mechanical properties.
• the cured perfluoroelastomers of the present invention are used in the preparation of manufactured articles as O-ring, gaskets, shaft seals, fuel hoses, etc., showing the combination of the above improved properties.
• fluoroelastomers are used for their high properties of chemical resistance, thermal resistance, good sealing properties and low permeability.
• the market request is to have available perfluoroelastomers having improved above properties. See for example patents EP 1,031,607, EP 1,031,606, U.S. Pat. No. 5,585,449, U.S. Pat. No. 5,948,868, U.S. Pat. No. 5,902,857.
• perfluoroelastomers are used up to temperatures of 230° C. If an improvement of thermal resistance is desired, it is necessary to use particular curing systems. See patents U.S. Pat. No. 5,902,857 and U.S. Pat. No. 5,948,868 wherein the crosslinking agent is a bis-olefin, which allows to obtain manufactured articles usable up to temperatures of the order of 300° C. Generally it is also known that by increasing the use temperature, for example from 275° C. to 300° C., the sealing and thermal resistance properties notably worsen.
• perfluoroelastomers are required, which, cured with conventional crosslinking agents, for example triallylisocyanurate can be mentioned, show an improved combination of the above properties, in particular an use temperature higher than those obtained by using this crosslinking agnt according to the prior art.
• the perfluoroelastomers on the market are usable at most up to 230° C.
• Perfluoroelastomers cured with triallylisocyanurate having a higher thermal rating are desired by users.
• Perfluoroelastomers are likewise required, which, cured with bis-olefins, show an improved combination of the above properties, in particular an use temperature higher than those obtained by using said crosslinking agents according to the prior art.
• the perfluoroelastomers on the market are usable at most up to 300° C. See for example patents U.S. Pat. No. 5,948,868 and U.S. Pat. No. 5,902,857.
• Perfluoroelastomers cured with bis-olefins having a higher thermal rating are desired by users.
• the Applicant has found a solution to the above technical problem and to obtain perfluoroelastomers having the combination of the above improved properties.
• An object of the present invention are perfluoroelastomeric gels having the following properties:
• the gel satisfying the following test the gel subjected to drying in a stove at 90° C. up to a constant weight gives a curable perfluoroelastomer.
• curable perfluoroelastomers From said curable perfluoroelastomers, cured perfluoroelastomers are obtained having an improved thermal resistance, improved sealing properties, improved mechanical properties compared with the perfluoroelastomers obtained according to the prior art, therefore not from perfluoroelastomeric gels.
• the invention perfluoroelastomeric gel contains TFE-based perfluoroelastomers with at least another (per)fluorinated comonomer having at least one unsaturation of ethylene type.
• the comonomer is selected from the following:
• CF 2 ⁇ CFOX (per)fluoro-oxyalkylvinylethers, wherein X is a C 1 -C 12 (per)fluorooxyalkyl, containing one or more ether groups;
• R′ Fn is equal to R Fn or OR Fn wherein R Fn is a linear or branched perfluoroalkyl radical with 1-5 carbon atoms, preferably R′ Fn ⁇ OCF 3 ;
• X 1n and X 2n equal to or different from each other, are F, CF 3 ;
• (per)fluorovinylethers of general formula CFX AI ⁇ CX AI OCF 2 OR AI (A-I) wherein R AI is a C 2 -C 6 linear, branched or C 5 -C 6 cyclic perfluoroalkyl group, or a C 2 -C 6 linear, branched perfluorooxyalkyl group containing from one to three oxygen atoms; R AI can optionally contain from 1 to 2 atoms, equal or different, selected from the following: Cl, Br, I; X AI ⁇ F; the compounds of general formula: CFX AI ⁇ CX AI OCF 2 OCF 2 CF 2 Y AI (A-II) are preferred, wherein Y AI ⁇ F, OCF 3 ; X AI as above; in particular (MOVE 1 ) CF 2 ⁇ CFOCF 2 OCF 2 CF 3 and (MOVE 2 ) CF 2 ⁇ CFOCF 2 OCF 2 CF 2 OCF 3 ; C 3 -C
• Preferred monomeric compositions of the perfluoroelastomers of the invention are the following, the sum of the comonomer percentages being 100%:
• TFE tetrafluoroethylene
• PAVE perfluoroalkylvinylether
• MOVE perfluorovinyl-ethers
• compositions are the following, the sum of the comonomer percent being 100%:
• perfluoroelastomers comprise also monomeric units deriving from a bis-olefin of general formula:
• R 1 , R 2 , R 3 , R 4 , R 5 , R 6 equal to or different from each other, are H or C 1 -C 5 alkyls;
• Z is a C 1 -C 18 linear or branched alkylene or cycloalkylene radical, optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical, as described in EP 661,304 in the name of the Applicant.
• Z is preferably a C 4 -C 12 , more preferably C 4 -C 8 , perfluoroalkylene radical, while R 1 , R 2 , R 3 , R 4 , R 5 , R 6 are preferably hydrogen;
• Z is a (per)fluoropolyoxyalkylene radical, it can comprise units selected from the following:
• Z has formula: -(Q) p —CF 2 O—(CF 2 CF 2 O) m (CF 2 O) n —CF 2 —(Q) p — (II)
• Q is a C 1 l-C 10 alkylene or oxyalkylene radical
• p is 0 or 1
• m and n are numbers such that the m/n ratio is between 0.2 and 5 and the molecular weight of said (per)fluoropolyoxyalkylene radical is in the range 500-10,000, preferably 700-2,000.
• Q is selected from:
• the bis-olefins of formula (I) wherein Z is an alkylene or cycloalkylene radical can be prepared according to what described, for example, by I. L. Knunyants et al. in “Izv. Akad. Nauk. SSSR”, Ser. Khim., 1964(2), 384-6.
• the bis-olefins containing (per) fluoropolyoxyalkylene structures are described in U.S. Pat. No. 3,810,874.
• the unit amount in the chain deriving from the bis-olefins of formula (I) is generally from 0.01 to 1.0 moles, preferably from 0.03 to 0.5 moles, still more preferably from 0.05 to 0.2 moles per 100 moles of the other above mentioned monomeric units, constituting the basic perfluoroelastomer structure.
• perfluoroelastomeric gel contains a semicrystalline (per) fluoropolymer, in an amount in per cent by weight referred to the total dry weight perfluoroelastomer+semicrystalline perfluoropolymer, from 0% to 70%, preferably from 0% to 50% by weight, still more preferably from 2% to 30% by weight, on the total of the monomer moles.
• semicrystalline (per)fluoropolymer it is meant a (per)fluoropolymer showing, besides the glass transition temperature Tg, at least a crystalline melting temperature.
• the semicrystalline (per)fluoropolymer is constituted of tetrafluoroethylene (TFE) homopolymers, or TFE copolymers with one or more monomers containing at least one unsaturation of ethylene type, in an amount from 0.01% to 10% by moles, preferably from 0.05% to 7% by moles.
• TFE tetrafluoroethylene
• Said comonomers having an ethylene unsaturation are of hydrogenated and fluorinated type.
• ethylene, propylene, acrylic monomers for example methylmethacrylate, (meth)acrylic acid, butylacrylate, hydroxyethylhexylacrylate, styrene monomers, can be mentioned.
• C 2 -C 8 hydrogenated fluoroolefins as vinyl fluoride (VF), vinylidene fluoride (VDF), trifluoroethylene, CH 2 ⁇ CH—R f perfluoroalkylethylene, wherein R f is a C 1 -C 6 perfluoroalkyl;
• C 2 -C 8 chloro- and/or bromo- and/or iodo-fluoroolefins, as chlorotrifluoroethylene (CTFE);
• CF 2 ⁇ CFOX (per)fluoro-oxyalkylvinylethers, wherein X is: a C 1 -C 12 alkyl, or a C 1 -C 12 oxyalkyl, or a C 1 -C 12 (per)fluoro-oxyalkyl having one or more ether groups;
• PAVEs in particular perfluoromethyl-, perfluoroethyl-, perfluoropropylvinylether and (per) fluorodioxoles, preferably perfluorodioxoles, are preferred comonomers.
• the semicrystalline (per)fluoropolymer is coated by a shell of a semicrystalline (per)fluoropolymer containing bromine and/or iodine atoms in the chain deriving from brominated and/or iodinated comonomers, in an amount from 0.1% to 10% by moles referred to the total moles of the basic monomeric units of the semicrystalline (per) fluoropolymer core+shell, the semicrystalline (per)fluoropolymer in the core and in the shell can be of different composition. See EP 1,031,606.
• the preparation of a perfluoroelastomers and the semicrystalline (per)fluoropolymers of the present invention is carried out by polymerization of the monomers in aqueous emulsion in the presence of an emulsion, dispersion or microemulsion of perfluoropolyoxyalkylenes, according to patents U.S. Pat. No. 4,789,717 and U.S. Pat. No. 4,864,006.
• the synthesis is carried out in the presence of a perfluoropolyoxyalkylene microemulsion.
• radical initiators for example, alkaline or ammonium persulphates, perphosphates, perborates or percarbonates, optionally in combination with ferrous, cuprous or silver salts, or other easily oxidizable metals, are used.
• surfactants of various type are optionally present in the reaction medium, among which fluorinated surfactants of formula: R 3 f —X k ⁇ M + are particularly preferred, wherein R 3 f is a C 5 -C 16 (per) fluoroalkyl chain or (per)fluoropolyoxyalkyl chain, X k ⁇ is —COO ⁇ or —SO 3 ⁇ , M + is selected among: H + , NH 4 + , or an alkaline metal ion.
• the polymerization reaction is generally carried out at temperatures between 25° C. and 150° C., at a pressure between that atmospheric up to 10 MPa.
• a further object of the present invention is a process to prepare perfluoroelastomer gels starting from a polymerization latex comprising the following steps:
• step Ao with dry weight of perfluoroelastomer+semicrystalline (per)fluoropolymer it is meant the residue weight after having dried the latex mixture in a stove at 90° C. until a constant weight.
• the perfluoroelastomer obtained at the end of the polymerization appears under aqueous latex form.
• the perfluoroelastomer concentration in the latex expressed in g of polymer/kg of latex, is between 50 and 600.
• the latex concentration for the process to form perfluoroelastomer gels of the present invention is in the range 50-300, still more preferably 100-250 g polymer/kg latex.
• Step A can be omitted when, after having carried out the optional step Ao, the perfluoroelastomer concentration is within the above ranges.
• the optional step A can be carried out even before the optional step Ao.
• step B the addition of one or more organic compounds soluble in the latex aqueous phase depends on the Tg (° C.) of the latex perfluoroelastomer.
• Step B is optional when the perfluoroelastomer has a glass transition temperature higher than 0° C.
• the organic compounds used in step B must be such, and/or added in an amount such as to lower the latex freezing point, without giving coagulation, down to a temperature value lower than or equal to the latex perfluoroelastomer Tg.
• those organic compounds lowering the freezing point of at least 1-2° C., more preferably of at least 3-6° C. with respect to the perfluoroelastomer Tg are preferred.
• step C as said, one or more organic compounds as defined in B can be used. Said compounds can be equal to or different from those used in step B.
• the amount of said organic compounds in the mixtures prepared in B and in C is generally from 5% to 70%, preferably from 10% to 50%, more preferably from 10% to 35%, referred to the total weight of the mixture. However the amount of said compounds is such to assure a freezing point of the mixtures prepared, respectively, in B and in C, with the above requirements.
• the soluble organic compounds in the latex aqueous phase usable in steps B and C of the invention process have a solubility in water higher than 1% w/w and are preferably liquid at room temperature (20-25° C.).
• C 1 -C 5 aliphatic alcohols for example ethyl alcohol, C 3 -C 4 ketones as, for example, acetone, diols for example ethylene glycol and propylene glycol can, for example, be mentioned; ethyl alcohol is preferred.
• Examples of electrolytes usable in C are inorganic salts, inorganic bases, inorganic acids.
• inorganic salts are aluminum sulphate, sodium sulphate;
• examples of inorganic bases are potassium hydroxide and sodium hydroxide;
• examples of inorganic acids are nitric acid, hydrochloric acid.
• inorganic acids more preferably nitric acid, are used.
• step F there is the gel formation from the polymeric latex.
• the latter is kept under stirring so that the gel remains in suspension and does not deposit on the reactor bottom.
• Soft stirrings for example from 10 to 100 rpm, can be used.
• step G the gel washing is generally carried out at temperatures between the one used in step F and 80° C., preferably from 10° C. to 40° C.
• temperatures between the one used in step F and 80° C. preferably from 10° C. to 40° C.
• neutral and/or acid aqueous solutions having pH from 1 to 7.
• the gel pH is brought to a value between 3 and 7, for example by washing with water.
• step H drying is carried out at temperatures in the range 60° C.-140° C., preferably 90° C.-110° C., until a constant weight of the residue.
• the process to form the gels of the present invention can be carried out batchwise or continuously.
• the invention perfluoroelastomeric gel allows to obtain manufactured articles having an improved thermal resistance, improved sealing properties, improved mechanical propeties compared with those obtainable with the perfluoroelastomers obtained by latex coagulation according to the prior art.
• a perfluoroelastomer which is crosslinked to produce manufactured articles to be used, as said, in the preparation of O-ring, gaskets, shaft seals, fuel hoses, etc., having an improved thermal resistance, improved sealing properties, improved mechanical properties in comparison with those obtainable according to the prior art.
• the perfluoroelastomers obtainable from the perfluoroelastomeric gel, for example by using the optional step H of the invention process, are cured for obtaining manufactured articles having the improved combination of the above properties.
• the perfluoroelastomer contains in the chain and/or in end position to the macromolecule iodine and/or bromine atoms.
• the introduction in the perfluoroelastomeric matrix of such iodine and/or bromine atoms can be carried out by the addition of brominated and/or iodinated “cure-site” comonomers, as bromo and/or iodo olefins having from 2 to 10 carbon atoms, as described, for example, in patents U.S. Pat. No. 4,035,565 and U.S. Pat. No.
• iodinated usable compounds are the tri-iodinated compounds deriving from triazines as described in the European patent application EP 860,436 and in the European patent application EP 979,832.
• the total iodine and/or bromine amount in end position ranges from 0.001% to 3%, preferably from 0.01% to 1,5% by weight with respect to the total polymer weight.
• perfluoroelastomers contain iodine; more preferably the iodine is in end position.
• chain transfer agents containing iodine and/or bromine In combination with the chain transfer agents containing iodine and/or bromine, other chain transfer agents Known in the prior art, as ethyl acetate, diethylmalonate, etc., can be used.
• peroxides capable to generate radicals by heating, for example: dialkylperoxides, in particular di-terbutyl-peroxide and 2,5-dimethyl-2,5-di(terbutylperoxy)hexane; dialkylarylperoxides as, for example, dicumyl peroxide; dibenzoyl peroxide; diterbutyl perbenzoate; di[1,3-dimethyl-3-(terbutylperoxy)butyl]-carbonate.
• dialkylperoxides in particular di-terbutyl-peroxide and 2,5-dimethyl-2,5-di(terbutylperoxy)hexane
• dialkylarylperoxides as, for example, dicumyl peroxide
• dibenzoyl peroxide diterbutyl perbenzoate
• di[1,3-dimethyl-3-(terbutylperoxy)butyl]-carbonate are described, for example, in patent applications EP 136,
• the peroxide amount is generally from 0.5% to 10% by weight with respect to the polymer, preferably 0.6%-4% by weight;
• curing coagents in amounts generally between 0.5 and 10%, preferably between 1 and 7%, by weight with respect to the polymer; among them, bis-olefins of formula (I); triallyl-cyanurate, triallyl-isocyanurate (TAIC), tris-(diallylamine)-s-triazine; triallylphosphite; N,N-dial-lyl-acrylamide; N,N,N′,N′-tetraallyl-malonamide; tri-vinyl-isocyanurate; and 4,6-tri-vinyl-methyltrisiloxane, etc., are commonly used: TAIC and the bis-olefin of formula CH 2 ⁇ CH—(CF 2 ) 6 —CH ⁇ CH 2 ;
• a metal compound in amounts between 1 and 15%, preferably from 2 to 10% by weight with respect to the polymer, selected from divalent metal oxides or hydroxides as, for example, Mg, Zn, Ca or Pb, optionally associated to a weak acid salt, as stearates, benzoates, carbonates, oxalates or phosphites of Ba, Na, K, Pb, Ca;
• mineral fillers such as mineral fillers, semicrystalline fluoropolymers in powder, pigments, antioxidants, stabilizers and the like.
• peroxidic crosslinking system comprising:
• crosslinking agent a bis-olefin having general formula:
• R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and Z are as above defined; the crosslinking agent amount generally being from 0.5% to 10% by weight with respect to the polymer, preferably 1%-5% by weight;
• peroxides capable to generate radicals by heating, for example: dialkylperoxides, in particular di-terbutyl-peroxide and 2,5-dimethyl-2,5-di(terbutylperoxy)hexane; dialkylarylperoxides such as for example dicumyl peroxide; dibenzoyl peroxide; diterbutyl perbenzoate; di[1,3-dimethyl-3-(terbutylperoxy)butyl-carbonate.
• dialkylperoxides in particular di-terbutyl-peroxide and 2,5-dimethyl-2,5-di(terbutylperoxy)hexane
• dialkylarylperoxides such as for example dicumyl peroxide
• dibenzoyl peroxide diterbutyl perbenzoate
• di[1,3-dimethyl-3-(terbutylperoxy)butyl-carbonate are described, for example, in patent applications EP 136,596 and EP
• the peroxide amount is generally from 0.5% to 10% by weight with respect to the polymer, preferably 0.6%-4% by weight.
• crosslinking agents preferably TAIC
• TAIC crosslinking agent
• the addition of small amounts of TAIC to the crosslinking system allows to further improve the perfluoro-elastomer properties as, for example, the thermal stability and the mechanical properties.
• the gel obtained with the invention process can be used to confer an improved chemical resistance and a reduced permeability to solvents, to sealing manufactured articles, for example O-ring or shaft seals, obtained with non fluorinated or fluorinated elastomers.
• the gel is preferably additioned of the crosslinking ingredients, for example those above mentioned, the obtained mixture is spread on the coating and is cured.
• non fluorinated elastomers examples include: polyisoprene, poly(styrene/butadiene), poly(acrylonitrile/butadiene), poly(ethylene/propylene/diene), polychloroprene, polyurethanes, polyisobutylene.
• fluorinated elastomers examples include VDF-based elastomers with comonomers as hexafluoropropene, methylvinylether, tetrafluoroethylene.
• the polymer Tg is determined by DSC on a latex portion, coagulated by conventional methods, for example in stove at 90° C. until a constant weight. See ASTM D 3418.
• the Applicant has found that the thermal stability of the manufactured articles obtained with the perfluoroelatomers of the present invention, for example O-ring, is maintained even over 300° C.
• n/m 10, having average molecular weight 600;
• n/m 20, having average molecular weight of 450.
• the autoclave was then heated to 80° C. and maintained at said temperature for the whole reaction. Then 35 g of 1,4-diiodoperfluorobutane (C 4 F 8 I 2 ) were introduced in the autoclave.
• TFE tetrafluoroethylene
• MVE perfluoromethylvinylether
• the bis-olefin addition was carried out in 20 portions, each of 0.9 g, starting from the polymerization start and for every 5% increase in the monomer conversion.
• TFE tetrafluoroethylene
• MVE perfluoromethylvinylether
• the autoclave After having fed 6,600 g of the monomeric mixture, the autoclave is cooled and the latex discharged. The reaction lasted on the whole 160 min.
• the so obtained latex has a concentration equal to 290 g polymer /kg latex and is used in the invention Examples and in the comparative Examples.
• n/m 10, having average molecular weight 600;
• n/m 20, having average molecular weight of 450.
• the autoclave was then heated to 80° C. and maintained at said temperature for the whole reaction.
• the autoclave was brought to the pressure of 0.6 bar (0.06 MPa) with ethane and then to the pressure of 20 bar (2 MPa) with a monomeric mixture constituted of 6.5% by moles of perfluoromethylvinylether (PMVE) and 93.5% by moles of tetrafluoroethylene (TFE).
• PMVE perfluoromethylvinylether
• TFE tetrafluoroethylene
• ammonium persulphate (APS) as initiator were then introduced in the autoclave.
• the so obtained latex is used in the Examples and in the comparative Examples.
• the content of the 30 l reactor is fed under stirring into the 50 l reactor, maintaining the temperature at ⁇ 9° C.
• the temperature is brought to 10° C. and one proceeds then to carry out 4 washings: for each of said washings 25 l of demineralized water are fed under stirring to the 50 l reactor. The material is let under stirring for 10 minutes, stirring is stopped and the aqueous supernatant phase is drained.
• the aqueous phase as a pH equal to 3.3.
• the perfluoroelastomeric gel is discharged from the reactor bottom.
• the obtained gel contains 42% by weight of perfluoroelastomer, density equal to 1.4 g/cm 3 , and it appears as a transparent gelatinous solid.
• the imbibition water is removed by pressing; it has a pH equal to 2.9.
• Successively the perfluoroelastomer is dried at 90° C. in an air-circulation oven for 16 hours.
• the obtained perfluoroelastomer is mixed by using an open mixer with the crosslinking ingredients reported in Table 1.
• the so obtained mixture is molded at 170° C. for 8 min.
• the polymer is discharged from the reactor bottom; the imbibition water is removed by pressing. Successively the polymer is dried at 90° C. in an air-circulation oven for 16 hours.
• the content of the 30 l reactor is fed under stirring into the 50 l reactor, maintaining the temperature at ⁇ 9° C.
• the temperature is brought to 10° C. and one proceeds then to carry out 4 washings: for each of said washings 25 l of demineralized water are fed under stirring to the 50 l reactor. The material is let under stirring for 10 minutes, stirring is stopped and the aqueous supernatant phase is drained.
• the aqueous phase has a pH equal to 4.
• the perfluoroelastomeric gel is discharged from the reactor bottom.
• the obtained gel contains 48% by weight of perfluoropolymer, density equal to 1.6 g/cm 3 , and it appears as a transparent gelatinous solid.
• the imbibition water is removed by pressing; it has a pH equal to 3.1.
• Successively the polymer is dried at 90° C. in an air-circulation oven for 16 hours.
• the obtained polymer is mixed by using an open mixer with the crosslinking ingredients reported in Table 1.
• the so obtained mixture is molded at 170° C. for 8 min.
• the material is let under stirring for 10 minutes, stirring is stopped and the aqueous supernatant phase is drained.
• the polymer is discharged from the reactor bottom; the imbibition water is removed by pressing. Successively the polymer is dried at 90° C. in an air-circulation oven for 16 hours.
• the latex obtained according to the Example A is gelled and the obtained gel washed according to the process described in the Example 1.
• the polymer is dried as described in the Example l and formulated as reported in Table 2.
• the so obtained blend is molded at 170° C. for 8 min.
• the latex obtained according to the Example A is coagulated and the obtained polymer washed according to the process described in the Example 2 (comparative).
• the polymer is dried as described in the Example 2 (comparative) and formulated as reported in Table 2.
• the so obtained blend is molded at 170° C. for 8 min.

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