CN1294601A - Perfluoroelastomer compsns. - Google Patents

Abstract

A perfluoroelastomer compound having improved processability comprising a perfluoroolefin, a perfluorovinyl ether, and a halogen-containing cure site component, wherein the polymer is substantially free of ionizable moieties; and preparing the Process for a copolymer; and articles made therefrom.

Description

perfluoroelastomer composition

field of invention

The present invention relates to peroxide-curable perfluoroelastomer compositions having good processability and good physical properties when vulcanized.

background of the invention

Perfluoroelastomers (elastic perfluoropolymers) are polymeric materials with outstanding high temperature durability and chemical resistance. Therefore, this composition is particularly useful as a seal and gasket in systems where high temperatures and/or aggressive chemicals are encountered. They are used in industries such as chemical processing, semiconductors, aerospace, petroleum, etc.

Much of the outstanding properties of perfluoropolymers can be attributed to the stability and inertness of the copolymerized perfluoromonomer units that make up most of the polymer backbone, such as tetrafluoroethylene and perfluoro(alkyl vinyl) ethers. In order to fully achieve the elasticity, the perfluoropolymer is generally crosslinked, eg by vulcanization. To this end, small amounts of cure site monomers are copolymerized with perfluoromonomer units. Sulfur site monomers containing at least one bromo or iodo group are known. When this cure site monomer is combined with peroxides and co-agents, it provides properly cured compositions.

Perfluoroelastomer is a very expensive material, so it is used only when no other material can do the job. Since the cost of raw materials is very high, it is necessary to keep the scrap rate during the molding operation to a minimum. However, perfluoroelastomers are known to be very difficult to process due to mixing, flow characteristics and mold release. When conventional initiators are used to prepare polymers such as persulfates, the end groups of the polymer generally have an ionic and/or acidic character. These typically present ionizable polymer end groups are prone to undesired reactions with certain commonly used additives such as acid acceptors. Examples of commonly used acid acceptors are zinc oxide, calcium hydroxide, calcium carbonate, magnesium oxide, and the like. They are used in compounding formulations to bind any HF or other acids that may be generated at the high temperatures at which perfluoroelastomers must function.

There is a great need for perfluoroelastomer compounds with good processability. Since many applications of these polymers also require good sealing capabilities, steps to improve processability preferably do not adversely affect key physical properties such as compression set resistance.

Overview of the invention

The perfluoroelastomer compound of the present invention adopts a perfluoroelastomer, and the elastomer is prepared by using an initiator mixture of an oxidizing agent and an R _f SO ₂ Na type perfluoroalkyl sulfinate. The copolymers produced in this way can surprisingly be processed like other elastomeric glues. They are readily processed in conventional mills or in mixing equipment, ie, mills or mixing equipment that do not require heating above room temperature. Their compound viscosity does not increase when acid acceptors such as Ca(OH) ₂ are added. Such perfluoroelastomers also have improved physical properties (such as resistance to compression set).

One embodiment of the present invention provides a peroxide-curable perfluoroelastomer compound that is easy to process and is substantially free of ionizable end groups. "Essentially free" of such end groups means that less than 10% of these end groups are ionizable groups. The compound for this example contains:

A) Perfluoroelastomers comprising copolymerized units derived from the following 1), 2) and 3), 1) perfluoroolefins, 2) selected from perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy Vinyl) ethers and perfluorovinyl ethers of their mixtures, and 3) a halogen group-containing cure site component capable of participating in a peroxide vulcanization reaction selected from the group consisting of at least one such halogen fluorinated olefins containing at least one such halogen group, fluorinated vinyl ethers containing at least one such halogen group, chain transfer agents containing at least one such halogen group and initiators containing at least one such halogen group, and their mixtures; provided that the cure site component is substantially free of nitrile groups, and

B) peroxide curing agent.

In another example, the present invention provides an easily processable peroxide-curable perfluoroelastomer compound comprising:

A) A perfluoroelastomer substantially free of ionizable end groups, wherein the perfluoroelastomer comprises copolymerized units derived from 1), 2) and 3) below, 1) a perfluoroolefin, 2) selected Perfluorovinyl ethers from perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers and mixtures thereof, and 3) vulcanization sites containing bromine or iodine atoms capable of participating in peroxide vulcanization reactions Components selected from brominated or iodinated olefins containing at least one such atom, brominated or iodinated vinyl ethers containing at least one such atom, brominated or iodinated chain transfer agents, brominated or Iodinated initiators, and mixtures thereof; and

B) peroxide curing agent.

The present invention also provides a method for improving the processability of perfluoroelastomers, which method comprises, under free radical conditions, combining perfluoroalkenes and perfluoroalkyl vinyl ethers or perfluoroalkoxy vinyl ethers and mixtures thereof , an aqueous emulsion of a polymerizable mixture of a halogen-containing cure-site component capable of participating in a peroxide cure reaction, a sulfinate salt of a fluoroaliphatic group, and an oxidizing agent capable of oxidizing the sulfinate to a sulfonyl group or The polymerization is carried out in suspension, provided that the cure site components are substantially free of nitrile groups.

The present invention also provides a method for improving the processability of perfluoroelastomers, which method comprises, under free radical conditions, combining perfluoroalkenes and perfluoroalkyl vinyl ethers or perfluoroalkoxy vinyl ethers and mixtures thereof , an aqueous emulsion or suspension of a polymerizable mixture of a bromine- or iodine-containing sulfur site component, a sulfinate salt containing a fluoroaliphatic group, and an oxidizing agent capable of oxidizing the sulfinate to a sulfonyl group .

The invention also relates to vulcanized and unvulcanized articles made from such vulcanizable compounds.

A detailed description

The compositions of the present invention comprise a peroxide-curable perfluoroelastomer characterized by improved processability and less reactivity with bases. These compositions comprise a) a perfluoroelastomer comprising interpolymerized units of a perfluoroolefin, a perfluorovinyl ether, and a cure site component containing at least one bromine or iodine moiety, and b) a vulcanizing compounds. Perfluoroelastomers are substantially free of ionizable end groups, such as those reactive with bases. This does not exclude the presence of vulcanization sites required for crosslinking in the perfluoroelastomer.

Examples of suitable perfluoroolefins useful in the present invention include tetrafluoroethylene and hexafluoropropylene.

Examples of suitable perfluorovinyl ethers are those of the formula:

CF ₂ =CFO(R _f O) _n (R' _f O) _m R _f (I) where R _f and R' _f are different linear or branched perfluoroalkylene groups containing 2-6 carbon atoms , m and n are independently 0-10, and R _f is a perfluoroalkyl group containing 1-6 carbon atoms.

A preferred class of perfluoro(alkyl vinyl) ethers includes the following compositions:

CF ₂ =CFO(CF ₂ CFXO) _n R _f (II) wherein X is F or CF ₃ , n is 0-5, and R _f is a perfluoroalkyl group containing 1-6 carbon atoms.

The most preferred perfluoro(alkyl vinyl)ethers are those wherein n is 0 or 1 and _Rf contains 1-3 carbon atoms. Examples of such perfluoroethers include perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether and perfluoro(propyl vinyl) ether. Other useful monomers include compounds of the formula:

CF ₂ =CFO[(CF ₂ ) _m CF ₂ CFZO] _n R _f (Ⅲ) where R _f is a perfluoroalkyl group containing 1-6 carbon atoms, m=0 or 1, n=0-5, Z =F or CF ₃ .

A good example _of this type of ether is one in which _Rf is _C3F7 , m=0 and n=1. Other perfluoro(alkyl vinyl) ether monomers useful in the present invention include compounds of the formula:

CF ₂ =CFO[(CF ₂ CFCF ₃ O) _n (CF ₂ CF ₂ CF ₂ O) _m (CF ₂ ) _p ]C _x F _2x+1 (IV) where m and n=1-10, p=0 -3, and x=1-5.

Good examples of ethers of this type include compounds wherein n=0-1, m=0-1 and x=1.

Examples of perfluoro(alkoxyvinyl)ethers useful in the present invention include:

CF ₂ =CFOCF ₂ CF(CF ₃ )O(CF ₂ O) _m C _n F _2n+1 (V) wherein n=1-5, m=1-3, and preferably n=1.

Specific examples _of perfluorovinyl ethers useful in _the present _{invention include CF2} = _{CFOCF2OCF2CF2CF3 , CF2} = _CFOCF2CF3 , _CF2 =CFO( _CF2 ) _3OCF3 and _CF2 = _CFOCF2 CF ₂ OCF ₃ .

Mixtures of perfluoro(alkyl vinyl)ethers and perfluoro(alkoxyvinyl)ethers may also be used.

Preferred copolymers consist of tetrafluoroethylene and at least one perfluoro(alkyl vinyl) ether as principal monomer units. In such copolymers, the copolymerized perfluoroether units comprise from about 15 to 50 mole percent of the total monomer units in the polymer.

The vulcanization site components used in the present invention are halogen-containing species that can participate in peroxide vulcanization reactions. Halogen is typically bromine or iodine. Suitable cure site components include terminally unsaturated monoolefins containing 2 to 4 carbon atoms such as bromodifluoroethylene, bromotrifluoroethylene, iodotrifluoroethylene and 4-bromo-3,3,4,4-tetrafluoroethylene Butene-1. _Examples of other _{suitable cure} site _{components include CF2} = _{CFOCF2CF2Br , CF2} = _{CFOCF2CF2CF2Br} , and _CF2 = _{CFOCF2CF2CF2OCF2CF2Br .} Preferably all or substantially all of these components are ethylenically unsaturated monomers.

Other useful cure site components are brominated or iodinated chain transfer agents and initiators. Examples of useful chain transfer agents include perfluoroalkyl bromides or iodides. _Examples of useful initiators include _{NaO2SC2F4OF4X} ( _where X is _Br or I).

Suitable peroxide curatives for use in the present invention are those which generate free radicals at the cure temperature. Dialkyl peroxides or bis(dialkylperoxides) which decompose at temperatures above 50° C. are particularly preferred. In many cases, it is convenient to use di-tert-butyl peroxide containing a tertiary carbon atom attached to the oxygen of the peroxy group. The most useful peroxides of this type are 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3 and 2,5-dimethyl-2,5-di (tert-butylperoxy)hexane. Other peroxides may be selected from such compounds as dicumyl peroxide, dibenzoyl peroxide, tert-butyl perbenzoate, α,α'-bis(tert-butylperoxy-diisopropyl benzene) and bis[1,3-dimethyl-3-(tert-butylperoxy)-butyl]carbonate. Generally, about 1-3 parts of peroxide are used per 100 parts of perfluoroelastomer.

Another material commonly blended with compositions that are part of a vulcanizing agent system is a co-agent consisting of a polyunsaturated compound capable of providing useful vulcanization in conjunction with a peroxide. For every 100 parts of perfluoroelastomer, these coagents can be added in an amount of 0.1-10 parts, preferably in an amount of 2-5 parts per 100 parts of perfluoroelastomer. Examples of useful coagents include triallyl cyanurate; triallyl isocyanurate; tris(methallyl)isocyanurate; tris(diallylamine)-s-triazine; Triallyl phosphite; N,N-Diallylacrylamide; Hexaallylphosphoramide; N,N,N',N'-Tetraalkyltetraphthalamide; N,N,N', N'-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinylmethyltrisiloxane; and tris(5-norbornene-2-methylene) cyanurate. Particularly useful is triallyl isocyanurate.

Other useful coagents include the dienes disclosed in EPA 0 661 304 A1, EPA 0 784 064 A1 and EPA 0 769521 A1.

Additives such as carbon black, stabilizers, plasticizers, lubricants, fillers and processing aids commonly used in the compounding of perfluoroelastomers may be added to the compositions of the present invention as long as they are relevant to the conditions of the desired application. suitable stability. Especially low temperature performance can be improved by adding perfluoropolyether (see US Patent 5,268,405).

Carbon black fillers can be used in elastomers as a means of balancing modulus, tensile strength, elongation, hardness, abrasion resistance, electrical conductivity, and processability of the composition. Suitable examples include MT carbon black (medium particle thermal black) designated N-991, N-990, N-908, and N-907, and large particle size furnace black. When using such large particle size carbon blacks, an amount of 1-70 phr is usually sufficient.

Additionally, fluoropolymer fillers may also be present in the composition. Generally, the amount of fluoropolymer filler used is 1-50 parts per 100 parts of perfluoroelastomer. The fluoropolymer filler can be a finely divided, readily dispersible plastic fluoropolymer that is a solid at the highest temperatures used to prepare and vulcanize the perfluoroelastomer composition. Solid means that the fluoroplastic, if partially crystalline, has a crystalline melting temperature above the processing temperature of the perfluoroelastomer. This fine, easily dispersed fluoroplastic is often referred to as fine powder or fluoroadditive. Fine powders are usually partially crystalline polymers.

The method of the present invention involves the use of a perfluorosulfinate and an oxidizing agent during free radical polymerization. The polymerization process involves free-radical polymerization of the individual monomers alone or in the form of solutions, emulsions or dispersions in organic solvents or water. Polymerizations in aqueous emulsions or suspensions are generally preferred because of rapid and nearly complete monomer conversion, ease of removal of the heat of polymerization, and ease of isolation of the polymer. Emulsion or suspension polymerization generally involves polymerizing monomers in an aqueous medium in the presence of an inorganic free radical initiator system and a surfactant or suspending agent.

Aqueous emulsion polymerization can be carried out continuously under steady-state conditions, for example, monomers, water, surfactants, buffers and catalysts are continuously fed into a stirred reactor under optimal pressure and temperature conditions, while continuous The resulting emulsion or suspension is drained. Another method is batch or semi-batch polymerization, which is to feed the components into a stirred reactor and make them react at a set temperature for a specified time, or add each component to the reactor, and then Monomers are fed into the reactor to maintain a constant pressure until the desired amount of polymer is formed.

A useful fluorine-containing aliphatic sulfinate of the present invention is disclosed in U.S. Patent No. 5,285,002, the content of which is incorporated herein by reference. The sulfinate can be represented by the following general formula:

R ³ _f SO ₂ M _1/x (Ⅵ) or

R ² _f [SO ₂ M _1/x ] _n (VII) wherein R ³ _f represents a monovalent fluorine-containing aliphatic group containing, for example, 1-20 carbon atoms, preferably 4-10 carbon atoms, and R ² _f represents a polyvalent, preferably divalent, fluorine-containing aliphatic group containing 1-20 carbon atoms, preferably 2-10 carbon atoms, and M represents hydrogen or a cation whose valence is x, and said x is 1-2, preferably 1, and n is 1-4, preferably 1 or 2.

The monovalent fluorine-containing aliphatic group R ³ _f is a fluorinated, stable, inert, non-polar saturated moiety. It can be linear, branched, and if it is large enough, cyclic or a combination thereof, such as an alkylcycloaliphatic group. Generally, ^R3f contains 1-20 carbon atoms, preferably 4-10 carbon atoms, and it contains 40-83 wt _% , preferably 50-78 wt% fluorine. Preferred compounds are those wherein the R ³ _f group is fully or substantially fully fluorinated, in which case R ³ _f is perfluoroalkyl, i.e. C _n F _2n+1 where n is 1 -20.

The polyvalent, preferably divalent, fluoroaliphatic group R ² _f is a fluorinated, stable, inert, nonpolar saturated moiety. It can be linear, branched, and if it is large enough, cyclic or a combination thereof, such as an alkylcycloaliphatic diradical. Generally, R ² _f contains 1-20 carbon atoms, preferably 2-10 carbon atoms. Preferred compounds are those wherein the R ² _f group is a perfluoroalkylene, i.e. C _n F _2n (wherein n is 1-20), or a perfluorocycloalkyl, i.e. C _n F _2n (wherein n is 5-20) compounds.

With respect to R ³ _f or R ² _f , divalent oxygen, hexavalent sulfur or trivalent nitrogen heteroatoms may be inserted in the skeleton chain of carbon atoms, and each heteroatom is bonded only to a carbon atom, but preferably when such a heteroatom exists atoms, such skeletal chains do not contain more than one such heteroatom for every two carbon atoms. An occasional hydrogen, iodine, bromine or chlorine atom attached to a carbon may be present; however, when such atoms are present, they are preferably not present in more than one for every two carbon atoms in the chain. When R ³ _f or R ² _f is or contains a ring structure, such structure preferably contains 6-membered ring atoms, one or two of which may be said heteroatoms, such as oxygen and/or nitrogen atoms. Examples of R ³ _f groups are fluorinated alkyl groups such as C ₄ F ₉ -, C ₆ F ₁₃ -, C ₈ F ₁₇ -, alkoxyalkyl groups such as C ₃ F ₇ OCF ₂ --. Examples of R ² _f are fluorinated alkylene groups such as -C ₄ F ₈ -, -C ₈ F ₁₆ -. When it is indicated that R ³ _f is a specific group such as C ₈ F ₁₇ -, it should be understood that such a group may represent the average structure of a mixed group such as C ₆ F ₁₃ - to C ₁₀ F ₂₁ -, said Mixed groups may also include branched structures.

Representative fluoroaliphatic sulfinate compounds useful in the methods of the present invention include the following:

NaO ₂ SC ₃ F ₆ O(C ₄ F ₈ O) _n C ₃ F ₆ SO ₂ Na, where n is 4-8.

Mixtures of mono-, di-, and tri-sulfinates can be used, depending on whether it is desired to use sulfinates as initiators, monomers, or both. When polyvalent sulfinates such as those represented by Formula VII are used, the sulfinate is monomeric and adds the fluorinated moiety to the polymer backbone. When a monosulfinate is used, the fluorinated moieties are added as polymer end groups.

The amount of fluoroaliphatic sulfinate used in the process of the invention can vary, for example, depending on the molecular weight of the desired polymer. The amount of the fluorine-containing aliphatic sulfinate is preferably 0.01-50 mole %, most preferably 0.05-10 mole % of the sulfinate compound based on the total amount of monomers.

In addition to sulfinates, other reducing agents may be present, such as sulfites, bisulfites, metabisulfites, dithionites, thiosulfites, sodium salts of phosphites, potassium Salt or ammonium salt, sodium or potassium formaldehyde sulfoxylate or hypophosphite. Activators such as ferrous, cuprous and silver salts may also be present.

The oxidizing agent used in the process of the present invention is water soluble which converts the sulfinate to the sulfonyl moiety. The sulfonyl groups produced by the process of the present invention are believed to scavenge _SO₂ and form fluorinated groups capable of initiating polymerization of ethylenically unsaturated monomers.

Many useful oxidizing agents are known and are disclosed in U.S. Patent 5,285,002. Representative examples of such useful oxidizing agents are the sodium, potassium and ammonium salts of persulfuric acid, perphosphoric acid, perboric acid, percarbonic acid, bromic acid, chloric acid and hypochlorous acid. Other useful oxidizing agents include cerium (IV) compounds such as (NH ₄ ) ₂ Ce(NO ₃ ) ₆ . It should be understood that this list of oxidizing agents is by way of example only. Those of ordinary skill in the art will appreciate that there are other useful oxidizing agents for the present invention based on the foregoing.

The amount of oxidizing agent used will vary depending on the particular oxidizing agent and sulfinate used. Generally, an equimolar amount or less (based on the amount of sulfinate) is used.

The vulcanizable compositions of the present invention can be prepared by mixing the perfluoroelastomer, peroxide vulcanizing agent, and other additives in conventional rubber processing equipment. Such equipment includes rubber mills, internal mixers such as Banbury mixers, and mixing extruders.

Prior to the present invention, it was difficult to prepare compositions containing perfluoroelastomers. Generally, such compositions require the use of heated processing equipment to prevent the composition from forming a brittle mass. The perfluoroelastomer compound of the present invention does not require the use of heated rollers or processing equipment during the mixing process. They can be prepared at ambient temperature without forming brittle masses. The substantial absence of reactive end groups on perfluoroelastomers is at least in part responsible for this. The substantial absence of these groups minimizes reactivity problems, such as exotherms or significant viscosity increases that occur during addition of the acid acceptor. Compound viscosity does not increase which prevents flow and cavity filling problems. The ability to mix at lower temperatures minimizes problems with premature initiation of vulcanization or crosslinking reactions.

The vulcanizable compositions of the present invention are useful in the manufacture of articles such as gaskets, hoses and seals. Such articles are made by molding under pressure a formulation of the vulcanizable composition with various additives, curing the part, and then subjecting it to a post-cure cycle. During the molding step, the perfluoroelastomers of the present invention also exhibit additional advantages. Faster mold filling or lower pressure required indicates less viscosity. Improved release is clearly seen when the press cured part or injection molded part is removed from the mold. The vulcanized composition has excellent thermal stability and chemical resistance. They are particularly useful in applications such as making seals and gaskets for semiconductor equipment and sealing for high temperature automotive applications.

The following examples further illustrate the invention. In these examples, properties were tested as follows.

Mooney viscosity was determined by ASTM D 1646-96 (ML 1+10 at 121°C). Results are reported in Mooney units.

According to ASTM D 5289-95, at 177 ° C, without preheating, the process time is 12 minutes (unless otherwise specified) and 0.5 ° arc, using Monsanto Moving Die Rheometer (MDR) model 2000 for mixing The mixture was subjected to vulcanization rheology test. Determine the minimum torque (ML) and maximum torque (MH) values, that is, the highest torque reached within the specified time without flat top or maximum value. Also record: t _s 2 (time for torque to increase to 2 units above ML), t'50 (time for torque to reach ML+0.5 [MH-ML]) and t'90 (time for torque to reach ML+0. 9[MH-ML] time). Torque is expressed in decinewton meters (dNm).

Molded samples (150 x 150 x 2.0 mm tablets unless otherwise stated) were prepared for the determination of physical properties by pressing at about 6.9 megapascals (MPA) for the indicated times and temperatures.

Post-vulcanized samples were prepared by placing the molded samples in a circulating air oven. The oven was maintained at the specified temperature and the samples were treated for the specified time.

The force per unit area is reported in megapascals (MPa).

The physical properties are determined according to ASTM D-412, and the hardness is determined according to ASTM D2240.

Compression set was determined by ASTM D 395-89 Method B at 200°C with a 0.139 inch (3.5 mm) O-ring pressed for 70 hours. Results are expressed in %.

Example 1

Several fluoropolymers were prepared in a manner similar to Example 1 of U.S. Patent No. 5,285,002, except that the monomers and other components used were expressed in grams by weight as follows. The monomers used are tetrafluoroethylene (TFE), perfluoromethyl vinyl ether (PMVE) and bromotrifluoroethylene (BTFE). Let (NH ₄ ) ₂ S ₂ O ₈ be APS. The fluoride sulfinate (C ₄ F ₉ SO ₂ Na) was prepared as described in U.S. Patent 5,285,002.

Comparative Polymer A Polymer A

Deionized (DI) water 2,777 2,774

C ₇ F ₁₅ COONH ₄ : 15.9 15.9

K ₂ HPO ₄ : 10 10

C ₄ F ₉ SO ₂ Na: ---- 4

Pre-added monomer:

TFE: 142 140

PMVE: 342 331

BTFE: 3.9 3

Injected APS: 2 3

monomer fed during the reaction time

TFE: 662 664

PMVE: 496 497

BTFE: 9.7 9.9

Polymerization was 651 minutes at 60°C for Comparative Polymer A and 262 minutes at 71°C for Polymer A. Both polymerizations were carried out at a pressure of 16 bar.

In both cases a water-clear transparent polymer latex was obtained. The latex _was coagulated using 30 g _Al2 ( _SO4 ) _3-18H2O in 1000 ml DI water. The polymer was filtered, washed several times with hot DI water, and dried overnight in a circulating air oven at 100°C to obtain a polymer gum.

Comparative Polymer A has a Mooney viscosity (ML 1+10 at 121° C.) of 76 compared to 96 for Polymer A.

Mix 100 parts by weight of each polymer glue by adding 15 parts by weight (phr) of N990 carbon black, 5 phr of zinc oxide, 1.5 phr of Luperco ^™ 101 XL organic peroxide from Atochem to each polymer glue. and 2 phr triallyl isocyanate-dry liquid concentrate (TAIC-DLC; 72% active) from Harwick.

Polymer A was compounded in a conventional manner on an open mill. Comparative polymer A had to be mixed on a heated (50-70°C) open mill because it would become brittle and turn into a powder if mixed in the conventional way (ie using standard or no heat conditions).

Table 1 lists the rheological data obtained from the MDR tests.

Table 1

MDR(177℃) Comparative Compound A Compound A

ML(dNm): 5.1 3.0

MH(dNm): 26 20

t _s 2 (minutes): 0.44 0.48

t'50 (minutes): 0.65 0.68

t'90 (minutes): 1.51 1.76

As can be seen from the MDR data, the ML (a measure of compound viscosity) of Comparative Compound A is significantly increased compared to Compound A, even though the Mooney viscosity of Comparative Polymer A is lower than that of Polymer A. In other words, even though the base polymer viscosity of Comparative Polymer A was lower than that of Polymer A, the addition of fillers, acid acceptors, and vulcanizing agents increased the compound viscosity of Comparative Compound A above that of Compound A viscosity.

After vulcanization of the compound, the data listed in Table 2 were obtained. Comparative Compound A was plate vulcanized for 10 minutes at 150°C, followed by post-cure for 16 hours at 150°C, and a further post-cure for 8 hours at 200°C. Compound A was vulcanized on a plate press for 10 minutes at 177°C, followed by post-cure at 200°C for 20 hours. Attempts to vulcanize and post-cure Comparative Compound A in the same manner as Compound A were unsuccessful due to warpage and crack formation in the test specimens.

Table 2

                                            Comparative Compound A 

Tensile Strength (MPa) 24.5 19.6

Elongation at break (%) 165 136

100% modulus (MPa) 14.1 12.7

Hardness (Shore A) 87 80 compression set O-ring, 70 hours at 200°C 42% 30%

The compression set resistance of Compound A was significantly better than that of Comparative Compound A. Comp A also required hot roll mixing, lower plate press cure temperature and two post cures.

Example 2

These samples were prepared to demonstrate the reactivity of the polymers when compounded with base or acid acceptors.

Polymer B was prepared in a similar manner to Polymer A except that 4 g of APS and _5.4 g of _C4F9SO2Na were used instead of _BTFE and the polymerization was carried out at a pressure of 11.6 bar.

Comparative Polymer B was prepared in a similar manner to Polymer B except that no sulfinate was used, only 1 gram of APS was used and the polymerization was carried out at a pressure of 11.0 bar.

The Mooney viscosity (ML 1+10 at 121°C) of Polymer B was 38 compared to 73 for Comparative Polymer B.

Comparative polymer B was compounded with 15 phr of MT N990 carbon black and 6 phr of Ca(OH) ₂ . During mixing, the components become exothermic when mixed and form a brittle compound. When the comparative compound B was tested by MDR at 177°C, the torque of the brittle rubber increased from the initial 3.4dNm to 17dNm within 30 seconds, and continued to increase to 20dNm within 10 minutes.

Polymer B was compounded with the same additives as Comparative Compound B. The ingredients were mixed on the mill to maintain a cohesive sheet with a torque rise of less than 1.1 dNm in 8 minutes at an MDR of 177°C.

These results show that the reactivity of the compounds of the invention is significantly lower when basic components such as acid acceptors are added. This difference is evident even in the absence of cure site components in the compound.

Claims (10)

1. An easy-to-process peroxide-curable perfluoroelastomer compound comprising: A) a perfluoroelastomer substantially free of ionizable end groups, said perfluoroelastomer comprising copolymerized units derived from 1), 2) and 3) below, 1) a perfluoroolefin, 2) selected Perfluorovinyl ethers from perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers and mixtures thereof, and 3) halogen-containing group vulcanization site groups capable of participating in peroxide vulcanization reactions The component is selected from the group consisting of fluorinated olefins containing at least one such halogen group, fluorinated vinyl ethers containing at least one such halogen group, chain transfer agents containing at least one such halogen group and containing at least one One such halogen group initiator, and mixtures thereof; with the proviso that the cure site component is substantially free of nitrile groups, and B) peroxide curing agent. 2. The perfluoroelastomer compound of claim 1, wherein the perfluorovinyl ether is selected from the group consisting of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether and perfluoropropyl vinyl ether ether. 3. The peroxide-curable perfluoroelastomer compound of claim 1 wherein the halogen in the cure site component is bromine or iodine. 4. The peroxide-curable perfluoroelastomer compound of claim 1, wherein the perfluoroelastomer is substantially free of ionizable end groups selected from carboxylate or carboxylic acid end groups and sulfonate or sulfonic acid end groups. 5. A method for improving the processability of perfluoroelastomers, which comprises, under free radical conditions, containing perfluoroalkenes and perfluoroalkyl vinyl ethers or perfluoroalkoxy vinyl ethers and mixtures thereof, capable of participating in peroxidation polymerizing an aqueous emulsion or suspension of a polymerizable mixture of a halogen-containing sulfidation site component of a compound sulfidation reaction, a sulfinate salt containing a fluoroaliphatic group, and an oxidizing agent capable of oxidizing the sulfinate to a sulfonyl group, The proviso is that the cure site component is substantially free of nitrile groups. 6. A method for improving the processability of perfluoroelastomers, which comprises under free radical conditions containing perfluoroalkenes and perfluoroalkyl vinyl ethers or perfluoroalkoxy vinyl ethers and mixtures thereof, bromine-containing or Polymerization is carried out using an aqueous emulsion or suspension of a polymerizable mixture of iodine sulfur site components, a sulfinate salt of a fluoroaliphatic group, and an oxidizing agent capable of oxidizing the sulfinate to a sulfonyl group. 7. A shaped article comprising the peroxide-curable perfluoroelastomer compound of claim 1. 8. The peroxide-curable perfluoroelastomer compound of claim 7, wherein the perfluoroolefin is tetrafluoroethylene and the perfluorovinyl ether is perfluoromethyl vinyl ether. 9. The peroxide-curable perfluoroelastomer compound of claim 1 wherein the cure site component is said chain transfer agent. 10. 2. The peroxide-curable perfluoroelastomer compound of claim 1, wherein the cure site component is said chain transfer initiator.