CA1210183A - Perfluoroelastomer blends - Google Patents

Abstract

TITLE
PERFLUOROELASTOMER BLENDS
ABSTRACT OF THE DISCLOSURE
Co-vulcanizable fluoroelastomer blends of tetrafluoroethylene/perfluoro-(methylvinyl-ether)/cure-site monomer terpolymer and hexafluoropropylene oxide/cure-site monomer dipolymer.

Description

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T ITLE
PERFLUOROELASTOMER BLENDS
DESCRI PTION
Technical Field This invention relates to certain vulcanizable fluoroelastomer compositions, which compositions are based upon co-vulcanizable blends of a major proportion of a tetrafluoroethylene/perfluoro-(methylvinyl 10 ether)/cure-site monomer terpolymer and a minor proportion o~ a high molecular weight hexafluoropropylene oxide (HFP0)/cure-site monomer dipolymer. Such blends are vulcanizable to useful elastomeric materials characterized by excellent 15 physical properties and resistance to environmental attack. These ma~erials can be fabricated into mechanical parts such as 0-rings, flange seals, gasket stocX, pump diaphragms and liners and are particularly useful where extraordinary resistance to 20 heat and corrosive fluids is required. In addition, Iow temperature properties are improved~ This invention also relates to improvements in the rheological and processing ch~racteristics of the tetrafluoroethylene/perfluoro-(methylvinyl ether)/cure-site monomer terpolymer by blending therewith a minor proportion of a co-vulcanizable, high molecuLar weight, hexafluoropropylene oxide/
cure-site monomer dipolymer.
Background Art U.S. Patent ~,546,186 granted December 8, 1970 to Gladding and Sullivan, discloses certain vulcanizable terpolymers derived from tetrafluoroethylene, perfluoro-(methylvinyl ether) and a cure-site monomer whinh can be, among other things, perfluoro (4-cyanobutyl vinyl ether) or n-2139 perfluoro (4-carbomethoxybutyl vinyl ether).

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U.S. P~tent 3,467,638 granted Sep~ember 16, 1969 to Pattison, discloses certain vulcanizable terpolymers derived from tetrafluoroethylene, perfluoro-(methylvinyl ether) and a cure-site monomer which can be, among other things, perfluoro (2-phenoxypropyllvinyl ether).
U,S. Patent 3,682,872 granted August 8, 1972 to Brizzolara and Quarles, discloses certain vulcanizable terpolymers derived from tetrafluoroethylene, per1uoro-(methylvinyl ether), and as a cure-site monomer, perfluoro (3-phenoxypropyl vinyl ether).
~ .S. Patent 4,281,092 granted July 28, 1981 to Breazeale, disclo~es certain vulcanizable copolymerQ of tetrafluoroethylene, per1uoro-(methylvinyl ether), and a cure-~ite mo~omer which can be perfluoro (8-cyano 5-methyl-3,6-dioxa-1-octene).
All of ~he above are examples of terpolymers which can be used a~ the ~ajor propo~tion o~ the blends of the present invention.
Copending Canadian Patent Application No.
399,788, filed 1982 March 30 of King and Krespan, discloses certain copolymers including hexafluoropropylene oxide/cure-site monomer dipoly~ers, where the cure-site ~ono~er can be a per~luoroglycidyl sther of the ~ormula C~/CFCF20RF

wherein ~ i5:
(i) -CFR'CFQ
Y Y' wherein R' is a carbon-carbon bond or a linear or branched perfluoroalkylene group of 1 to 12 carbon atoms; Q is -CN, or -OC6F5, and Y and Y' are -~ or -CF3, or ( i i) -CF(R2)

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wherein R' is -CF2CN; or ( i ii) -~CF2CFo)mR3Q

wherein R3 is a linear or branched perfluoroalkylene group of carbon content such that the moiety -~CF2cFo)mR3 does not exceed 15 y carbon atoms: Y independently is -F or CF3; M is 1 to 4; and Q i5 as de~ined above; or ~ iv) -C6F5 ' High mole~ular weight dipolymers of hexafluoropropylene oxide and a cure-site monomer a~
disclosed in the above-mention~d Canadian Application 399,788 can be prep~red according to the technique dis-closed in copending Canadian Patent Applicat$on No.
399,790, f.iled 1982 March 30 o~ Darling. That applica-tion discloses a process for purifying hexafluoropro-pylene oxide, which process permits the achievement ofhigh degrees of polymerization (200 or more).
The dipolymers described above are examples of hexafluoropropylene oxide/cure-site monom~r dipolymers which can be u~ed as the minor proportion of the blends of the present invention.
Disclosure of the Invention The present invention relates to ~luoroelastomer compositions comprising co-vulcanizable blends of at least one terpolymer and at least one dipolymer7 the at least one terpoly~er as3 should comprise from 50 to 95 percent by weight of the fluoroelasto~ler blend and will be a tetrafluoroethylene/perfluoro-~methylvinyl ether)/cure-site monomer terpolymer where the cure-site monomer will have a functional moiety selected from the group consisting of -CN and -C6F5. Preferably the terpolymer will have an inherent viscosity of at least 0.4. Examples of suitable cure-site monomers are disclosed in U.S.
Patents 3,546,186: 3,467,638; 3,682,872; and 4,281,092, cited and discussed above~
The dipolymer should comprise from 5 to 50 percent by weight of the fluoroelastomer blend and will be high molecular weight (number average molecular weight of at least 15,000 or degree of polymerization of at least 90) hexafluoropropylene oxide/cure-site monomer dipolymer having an average cure-site monomer concentration of 2 per polymer chain where the cure-site monomer has the same functional moiety as in the terpolymer. It i~
important that the reactive functional group on the - cure-site monomer be the same in the terpolymer and the-dipolymer so that the blend is co-vulcanizable-and so that the cure rate of each of the blend components are approximately equalO Otherwise the dipolymer has a tendency to separate from the vulcanizate, the separation becoming manie~t by the presence of an oily exudate on the surface of the finished part. Failure to achieve co-vulcanization results in a product with inferior physical properties as well as undesirable sur~ace characteristics.
Preferably the blends will contain about 65-80 weight percen~ of the terpolymer and 20-35 weight percent of the dipolymer. Preferably the dipolymer will be high molecular weight, i.e., at least 20,000 or having a degree of polymerization of at least 120.
Compounding, curing and molding o~ the fluoroelastomer blends of the present invention will be done as would be done for the terpolymer alone, and as disclosed in U.S. Patent 4,281,092.
Blending of the dipolymer with the terpolymer can be conveniently done, during 10 compounding of the terpolymer, and will conveniently be accomplished by mixing on a 2-roll rubber mill for about 60 minutes at a temperature of about 65C.
Preferably, the dipolymer i8 predispersed on the flller (e.g. carbon hlack~ by rolling in a jar for an 15 extended period (e.g. overnight). The dispersed dipolymer is then more easil~ incorporated into and blended with the terpolymer than would be the case without predispersion on ~iller.
In the following examples, there are ~hown 20 specific embodiments of the present invention in direct side-by-side ~omparison wit:h embodi~nents o contsol experiments where, for ~xample, the blends are not co-~ulcanizahle or there is no blend at all.
It will be seen that the blends of the present invention do not exude dipolymer to ~he surface, hav~
low~r hardness, Tg and Clash 8erg temperature values and/o~ superior tensile and set properties~
The polymers are as defined in the Tables I
and II and were prepared generally as described in 30 U.S. Patent 4,281,092 and Canadian Patent Applications 399,788 and 399,790, a~ appropriate.
More specifically, polymer A in Table I was prepared by polymerization in a 3800 ml mechanically agitated, water-jacketed, stainless steel autoclave 35 operated continuously at a temperature of 70C and a ~Z~ 3 pressure of 4.8 MPa. Tetrafluoroethylene and perfluoro-(methylvinyl ether) were pumped in at the rate of 220 and 300 g/hr respectively, by means of a diaphragm co~pressor. Perfluoro-(8-cyano-5-methyl-

3,6-dioxa-looctene) was fed neat at the rate of 15.8 g/hr (41 mmole/hour). Each of two aqueou~ redox initiator solutions were pumped in separately at the rate of 600 ml/hr~ The peroxide initiator solution A
was prepared by dissolving 125 g ammonium persulfate, 80 g disodium phosphate hepta-hydrate and 200 g ammonium perfluorooctanoate in 8 liters de-aerated distilled water. Initiator solution B was prepared by dissolving 103 g sodium sulfite in 8 1 de-aerated distilled water.
Polymer latex was removed continuously through a let-down valve and unreacted monomers were vented. Over a period of 9.5 hours 4S liters latex was collected.
Latex was coagulated by adding it to a solution consisting of 382 g magnesium chloride hexahydrate in 8.5 liters water, 8.5 liters ethanol, and 10 ml dilute sulfuric acid. The coagulated polymer was washed and isolated in the three~tank cascade process described in U.S. Patent No.
3,752,789. The wet crumb was dried by heating in air at 75C for eight hours, then for two days at 125C
in a vacuum oven. The yield of terpolymer was 3.7 kg. It contained about 34 mole %
perfluoro-(methylvinyl ether), about 0.8 mole %
30 perfluoro-(8-cyano-5-methyl-3,6-dioxa-1-octene), and had an inherent viscosity of 0.70 dl/g (measured in a solution containing 0.1 gram of polymer per 100 grams of solvent consisting of a 60/40/3 volume ratio of hepta-fluoro-2,2,3-trichlorobutane, 35 perfluoro-(butyltetrahydrofuran) and diethylene glycol dimethyl ether.

Polymer B in Table I was prepared by the same procedure as was used to prepare polymer A
e~cept that perfluoro-(2-phenoxypropyl vinyl ether) was used in place of perfluoro-(8-cyano-5-methyl-3,6-dioxa-l~octene).
Polymer C in Table II was prepared by copolymerization of perfluoro-(6,7-epoxy-4-oxaheptanenitrile) with hexafluoropropylene oxide.
The nitrile was prepared in a 100-ml stainless steel-lined tube charged with perfluoro-(4-oxa-6-heptanenitrile) which was heated at 140C while oxygen was added incrementally until reaction was complete. Fractionation of the liquid products gave the desired epoxynitrile. Polymerization catalyst was prepared by reacting cesium fluoride, tetraglyme and hexafluoropropylene oxide tetramer under agitation for at least si~ hours. The reaction mixture was centrifuged for 30 minutes at 0C. Four millimoles of the catalyst was injected into a thoroughly dried 4-neck 500 ml flask and cooled to -35C. Hexafluoropropylene (dried by passing through molecular sieves) was added at a rate of 1 g/min for a total of 20 g. Hexafluoropropylene oxide (179 g) (dried by passing over KOH and CaH2) was added at a rate of 0.07 g/min and 4.68 grams of the epoxynitrile was added at a rate of 0.13 g/h~ After 47.6 hours of reaction at -33 to -35C, the unreacted gases were removed by applying vacuum. The polymer mixture was then brought slowly to 100C under vacuum to remove any unreacted monomers. Quantitative infrared analysis on the acid fluoride end group indicated a number average molecular weight of approximately 40,000. The amount of incorporated epoxynitrile was 2.5~ (by weight) by nitrogen analysis.

:~2~?'~83 Polymer D in Table II wa~ prepared by hydrolysis of the acid fluoride groups in polymer C
to carboxyl.
Polymer E was prepared by ~opolymerization of perfluoro-(phenyl-2,3-epoxypropyl ether) with hexafluoropropylene oxide substantially as described in the prepara~ion of polymer C, abov~.
Perfluoro-tphenylallyl ether) was obtained by adding perfluoroallyl ~luorosulfate rapidly to an equivalent of cesium pentafluorophenoxide in diglyme at -25-, The temperature carried to ~10, and the produc~ was isolated by drowning the reaction mixture in water, wa~hing the lower layer with water, and drying and distilling, bp 63- (30 mm).
A 100-ml metal tube eharg~d with perfluoro-(phenylallyl ether) W~5 heated at 140 while oxygen was passed in until uptake ceased.
~istillation gave a mixture of per~luoro-~phenyl-2,3-epoxypropyl ether) and starting material. Thi~ distillate was stirred with CFC12CF2Cl and bromine while the mixture was i~radiated with a sunlamp at 40~55- for 18 min.
Dis~illation gave nearly pure epoxide. ~he several ractions were contacted with calcium hydride while open to the ai.r until the acid fluoride impurity peak in the infrared spectru~ disappeared, and were then ~ubjected to vacuum transfer, contact with CaS04, and filtration to give purified per~luoro-tphenyl-2,3-epoxypropyl ether). 7~36 9 o the perfluoro-(phenyl-2,3-epoxypropyl ether) and 138 g o~ hexafluoropropylene oxide were copolymerized at -32 to -35C over a period of 48 hour~. Quantita~ive infrared analysi~ on the the acid fluoride end group indicated a number average molecular weight of approximately 2S,000.

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Polymer F WAS prepared by homopolymerization of hexafluoropropylene oxide using a monofunctional initiator. ~he monofunctional initiator solution was prepared by reacting 2.09 grams of effectively dried (accordin~ to procedures described in U.S. Patent 3,660,315) high purity cesium fluoride with 10.1 grams of perfluorinated acid fluoride, which was an oligomer of HFPO with a number average molecular weight of 845 and an average degree of polymerization 10 of approximately 5 (prepared according to procedures described in U~S. Patent 3,412,148). The cesium fluoride and the acid fluoride were reacted in a Pyrex shaker tube containing six grams of tetraglyme which had been freshly di~tilled rom lithium aluminum hydride. Stsictly anhydrous procedures were observed throughout. The mixture was shaXen f~r 6 hours to assure complete reaction. Exces~ ce~ium fluoride was driven to the bottom of the tube by centrifugation. The cl~ar, liquid initiator 2~ contained approximately 4 millimoles of active cesium alkoxide per ~illilites.
The polymerization vessel consisted o~ a fully glass jacketed four neck round bottom reactor which is equipped with a paddle stirrer, re~lux condenser cooled with solid carbon dioxide, ga~ inlet port and a thermocouple well. The entire reactor was dried thoroughly at 200-C in a dry nitrogen atmosphere and was assembled and kept dry with a blanket of high purity dry nitrogen. Methano~ wa used as a co~lant and was pumped throu~h the coolant jacket ~rom a Neslab ULT80~1OW temperature circulator and refrigexator systemO With the reactor at room temperature 4 milliliters of initiator prepared as in Example 1 was introduced by means of 2yringe ~nd the reactor was cooled to an lnternal temperature of *denotes trade mark.

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between -30 to -34C. Liquified hexafluoropropylene was used as a solvent to dilute the cold viscous initiator solution. The addition rate for the hexafluoropropylene was 1 gram per minute ~or a total S of ~0 grams. With slow stirring, purified hexafluoropropylene oxide purified in a two-stage (potassium hydroxide/calcium hydride) scrubber as described above was added as a gas in a semi-batch ~ashion at a rate of 11 milliliters per minute for a period of 20 hours. Throughout the reaction period the polymer mixture appeared as a clear and increasingly viscous liquid. Toward the end o~ the addition period the solution became extremely difficult to stir effectively and a further dilution with additional hexafluoropropylene was necessa~y.
The reaction mixture was allowed to stand for approximately two hours to consume unreacted hexafluoropropylene oxide. ~0 grams of hexafluoro-propylene~was added to the reactor at a rate of 1 gram per minute. The reaction mixture became less viscous and re~ained clear and could ~e ef~ectively stirred. The addition of hexafluoropropylene oxide was resumed at the same rate of 11 milliliters~per minute. ~t the- end of 21 hours the reaction mixtur~
had once again become very viscous and very difficult to stir effectively. The monomer feed was stopped and the reac~or was allowed to stand for an additional three hours to assure complete reaction with residual hexafluoropropylene oxide. A vacuum was applied to the reactor to remove the hexafluoropropylene diluent at low temperature. Once most of the hexafluoropropylene was removed the reactor was slowly warmed to room temperature. The extremely viscous and frothy polym0r was stirred slowly with a paddle stirrer to remove the last ll traces of diluent. The polymer had a ~endency to climb the shaft of the reactor stirrer but would flow back down into the reactor upon further warming of the polymer. Warm polymer was removed from the reactor under anhydrous conditions to preserve the acid fluoride end group. Quantitative infrared analysis on the acid fluoride end group indicated a number average molecular weight of approximataly 45,000. This polymer was neutralized with aqueous potassium hydroxide, then dried in a vacuum oven at ~150C for three days, and finally centrifuged to remove suspended solids.
The polymer blends were compounded and cured as described in 4,281,092 and the results of evaluation of the surface and physical properties of the vulcanizates are described in Tables III and IV.
All par~s and percentagPs are by weight and all temperatures are in degrees Celsius unless otherwise specified. Measurements not originally in SI units have been so converted and rounded where appropriate.

TABLE I
Tetraf~uoroethylene/Perfluoro-(methylvinyl ether)/Cure-site monomer Terpol~mers . _ .
Inh. Composition (weight percent?
Polymer Visc. PMVE Cure-Site Monomer Wt. %
A 0.7045.5 Perfluoro-(8-cyano- 2.6 5-methyl-3,6-dioxa-l-octene) B 0.5642.5 Perfluoro-(2-phen- 1.9 oxypropyl vinyl-ether) TABLE II
Hexafluoro~ropylene oxide/Cure-site monomer Dlpolymer MnCure-Site Polymer X 103 Monomer Wt. %
C 40 Perfluoro-(6-7-epoxy- 2.5

4-oxaheptane nitrile) D 40 Polymer C in which 2.5 end groups were hydrolyzed to carboxyl groups E 25 Perfluoro-(phenyl- 3.7 2,3-epoxy-propyl ether) F 45 None 0 ~2~ il3 TABLE III
BLENDS OF T~RPOLYMER A ~I~H HFPO POLYM~RS
Example 1 2 - 3 4 Co~pound Recipe (parts by weight) Polymer A 69 75 90 80 Polymer C or D 31C 25C 10D 20D
Tetraphenyltin 2.9 3.0 2.9 3.3 18-crown-61 0.10 0.15 0.13 0.11 SAF Black 9.8 15 15 15 Glass Transition 10 Temp. (C by DSC2) - - -10 -15 ~lolded (30 min/210C) and Post-Cured Dry Dry Dry Dry Vulcanizate Properties Glass Transition 15 Temp (C by DSC2) -20 -23 -14 -20 Clash-Berg Temp. (oC)4 - -13 -8.5 -12 Tensile Test5 Stress at 100% Elong. (MPa) - 6.2 2.5 2.2 Stress at Break (MPa) - 8.7 10.3 7.1 Elongation (%) - 120 190 170 Compression Set6 #214 O-rings %) 32 22 43 46 Yerzley Pellets (%) - 18 19 20 Hardness, Shore A 67 64 66 61 _ 25 1. 1,4,7,10,13,16-hexaoxacyclooctadecane 2. Differential scanning calorimetry 3. Post-cured under nitrogen - ~rime (hr)/Te~p. (C) 6 / 25~ 204 6 / 204--~288 4. ASTM -D1043, 69 MPa

5. ASTM - D412, Me~hod A, Small Dumbbells, 25C
3~ 6. ASTM - D395, 70 hr/204C

TABLE III (CONT'D.?
BLENDS OF TERPOLYME~ A WITH_~FPO POLYMERS
Nor.-co-curing Blend Control Example 5 6 7 Compound Recipe (parts by weight) Polymer A 90A 80A lOOA
Polymer F 10F 20F O
Tetraphenyltin 3.0 3.0 3.0 18-crown-6l 0.20 0.20 0.10 SAF Black 15 15 15 10 Glass TransitiOn Temp. (C by DSC2) -13 -20 -8 Molded (30 min/210C
and Post-Cured Oily Oily Dry surface puddles Vulcanizate Properties 15 Glass Transition Temp (C by DSC2) -12 -12, -587 -8 Clash-Berg Temp. (oC)4-9 -ll -4 Tensile Test5 Stress at 100~ Elong. (MPa) 2.31.8 5.9 Stress at Break (MPa) 6.8 3.5 lO.g 20 Elongation (~) 210 l90 140 Com~ression Set6 #214 O-rings (~~) 22 64 36 Yerzley Pellets (~) - - 15 Hardness, Shore A 65 60 72 l. 1,4,7,10,13,16-hexaoxacyclooctadecane 2. Differential scanning calorimetry 3. Post-cured under nitrogen - Time (hr)/Temp. ~C)

6 /25-~204 6 /204-~288 4. ASTM D-1043, 69 MPa 5. ASTM - D412, Method A, Small Dumbbells, 25C
6. ASTM - D395, 70 h~/204C

7. Indicates separate phase poly HFPO

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TABLE IV
BLENDS OF TERPOLYMER B WITH HFPO DIPOL~MER
Control Example 8 9 10 5 Compound Recipe (parts by weight) Polymer B 70 90 100 Polymer E 30 10 0 DCH-18~crown-614 4 4 PbO 4 ~ 4 10 SAF Black 10 10 10 Glass Transition T C by DSC3-12,-574 -14 -2 (-15, -12) Molded (60 min/190C) and post-cured 5 Dry Dry Dry Vulcanizate Properties Glass Transition Temp. (C) By DSC3 -26 -19 -2 By TMA6 -19 - --20 Clash-Berg Temp. (oC)7 -16 -5 ~1 T`ensile Test8 Stress at 100% Elong. (MPa) 4.1 8.3 10.0 Stress at Break (MPa). 8.6 15.2 17.9 Elongation ~) 170 140 155 Compression Set9 25 #214 O-rings (~) 84 70 60 Yerzley Pellets (~)69 52 43 Hardness, Shore A 68 74 78 1. Dicyclohexyl-18-crown-6 2. Dipotassium salt of bis-phenol AF
3. Differential scanning calorimetry 4. In~icates separate phase pol~-HFPO
5. Post cured under nitrogen (Time hr/Temp. C) 6/25 to 204 6/204 to 288 6. Thermomechanical analysis 7. ASTM D-1043, G9 MPa

8. ASTM D-412, Method A, Small Dumbbells, 25C

9. ASTM D-395, 70 hr/204C

Industrial Applicability -The fluoroelastomer blends of the present invention are useful in the manufacture of ~inished parts surh as 0-rings, flange seals, gasket stock, pump diaphragms and liners. The extraordinary physical properties and resistance to environ~ental attack of such parts made from these compositions make them particularly well suited for applications in process streams subject to severe fluid service at in-line temperatures as high as 700~F or in streams carrying highly corrosive fluids, such as hydrogen sulfide.
Best Mode Although the best mode of the present invention~ i.e., the single best fluoroelastomer blend of the present invention, will depend upon the particular desired end use and the specific requisite combination of properties for that use, the single most preferred composition of the present invention 20 is that described in detail in Example 2.

Claims (8)

1. A co-vulcanizable fluoroelastomer blend consisting essentially of (a) 50-95 weight percent of at least one tetrafluoroethylene/perfluoro-(methyl-vinyl ether)/cure-site monomer terpolymer and (b) 5-50 weight percent of at least one hexafluoropropylene oxide/cure-site monomer dipolymer, wherein the reactive functional group of the cure-site monomer in the terpolymer is the same as in the dipolymer and is selected from the group consisting of -C6F5 and -CN.

2. The blend of Claim 1 wherein the terpolymer comprises 65-80 weight percent of the blend and the dipolymer comprises 20-35 weight percent.

3. The blend of Claim 1 wherein the terpolymer cure-site monomer is perfluoro-(8-cyano-5-methyl-3,6-dioxa-1-octene).

4. The blend of Claim 1 wherein the number average molecular weight of the dipolymer is greater than 15,000.

5. The blend of Claim 1 wherein the terpolymer cure-site monomer is perfluoro-(2-phenoxypropyl vinyl ether).

6. The blend of Claim 1 wherein the dipolymer cure-site monomer is perfluoro-(6,7-epoxy-4-oxaheptane nitrile).

7. The blend of Claim 1 wherein the dipolymer cure-site monomer is perfluoro-(phenyl-2,3-epoxypropyl ether).

8. The blend of Claim 1 wherein the terpolymer has an inherent viscosity of at least 0.4.