CA1222849A

CA1222849A - Fluoroelastomer curatives

Info

Publication number: CA1222849A
Application number: CA000422120A
Authority: CA
Inventors: Carl A. Aufdermarsh
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1982-02-25
Filing date: 1983-02-22
Publication date: 1987-06-09
Also published as: EP0087775B1; AU553133B2; JPS58152041A; BR8300831A; DK87683A; NO161804C; NO830646L; JPH033708B2; DK87683D0; NO161804B; EP0087775A1; US4394489A; AU1180483A; DE3364306D1

Abstract

TITLE
FLUOROELASTOMER CURATIVES
ABSTRACT OF THE DISCLOSURE
Allyl-, propargyl- and allenyl- tin curatives for fluoroelastomers with nitrile cure sites provide rapid curing combined with excellent stability in aqueous environments.

Description

~2;2~ L9 TITLE
FLUOROELASTOMER CURATIVES
BACKGROUND OF THE INVENTION
Per~luoroelastomers, providing, as they do, excellent physical properties and resistance to environmental attack, are widely used in applications where extraordinary resistance to heat and corrosive fluids is required Elastomers of this type that ~
contain a reactive nitrile cure site can be cured or 10 vulcanized with a curative that joins the nitrile -cure sites into a triazine~ A wide variety of curatives or accelerators has been suggested in the past, of which tetra~henyltin has been found to be especially satisfactory. ~owever, continuing effort has been directed toward the development of new curing agents which provide more rapid and complete vulcanization at lo~ and moderate temperatures and which result in a cured product exhibiting resistance to the broadest possible range of environments.
SUMMARY OF THE INVENTION
The instant invention provides perfluoroelastomer compositions containing a curing agent which provides rapid and more complete vulcanization and which results in a final product that is particularly resistant to aqueous environments.
Specifically, the instant invention provides, in a nitrile-substituted fluoroelastomer containing a curing agent, the improvement wherein the curing agent comprises about from 1 to 10 parts per 100 parts by weight of elastomer of an organotin compound having the general formula RxSnY4_x wherein x-is ~-3, R is aryl of 6-10 carbon atoms or alkyl of 1-4 carbon atoms, and Y is at least one of AD 5194 35 allyl, propargyl and allenyl.

2~3~9 Detailed Description oE the Invention The ins-tant invention is applicable to fluoroelastomers containing nitriLe cure si-tes. ,Such elastomeric compositions can be prepared, for example, by copolymerizing tetrafluoroethylene, perfluoromethylvinyl ether, and a third monomer containing a nitrile cure si-te. Other fluoroelastomers which can be used are those prepared Erom combinations oE vinylidene fluoride, hexaEluoropropylene, and tetrafluoroethylene and a monomer contalning a nitrile cure si-te. The preparation oE speciEic fluoroelas-tomers oE -this type is described in detail in Gladding et al. U.S. Paten-t

3,546,186; Nottke U.S. Patent 3,933,767 and Breazeale U.S. Patent 4,281 092. Those nitrile-substituted fluoroelastomers prepared :Erom tetrafluoroethylene, perfluoromethyl perfluorovinyl ether and cyano-substi-tuted perfluorovinyl ether described in U.S.
Patent 4,281,092, as well as copolymers of hexafluoropropylene oxide with nitrile-substituted perfluoroalkylene oxides have been found to be particularly satisfactory in combination with the curing agen-ts of the present inven-tion. The preparation of polyhexafluoro propylene oxide and i-ts copolymers is described in the copending Canadian Patent application No. 399 78~ of A.P. King and C.G. ~respan, filed 1982 March 30.
The curing agents used in the present invention are organotin compounds of the general formula RxSnY4_x, wherein x is an integer of from 0-3, providing at leas-t one Y substituent in the tin compound, and wherein Y is at least one of allyl (CH2CH=CH2), propargyl (CH2C=CH), and allenyl (CH=C=CH2). The remaining organic moieties, represented by R, can be aryl or alkyl moie-ties.

Aryl substituents which can be used include those having 6-10 carbon atoms such as phenyl, toluyl and substitu-ted phenyl moieties. Alkyl R yroups which can be used include those having frorn 1-~ carbon a-toms such as methyl, ethyl, propyl and buty:L. While the behavior o~ any curing agent of -the presen-t invention will vary with the particular organic substituents, in general, the curing rate of the polymer will increase with the number of allyl, propargyl or allenyl groups present.
The amount of curing agent used will necessarily depend on the degree of crosslinking desired in the final product as well as the number of nitrile cure sites present in the fluoroelastomer. A
marked molar excess of curing agent over the nitrile cure sites available in the fluoroelastomer may somewhat increase the curing rate, but will have little effect on the final properties of the cured polymer. In general, about from 1-10 parts by weight per one hundred parts o~ elastomer can be used, and about from 3-5 parts of curing agent per 100 parts of elastomer have been found to be particularly satisfactory for most applications.
The organotin curing agents used in the present invention can be prepaxed according to known -techniques, as described, for example, in D. Seyferth and M.A. Weiner, J. Org. Chem. 26 pp 4797-4800 (1961). In accordance with these procedures, polyorganotin halides are reacted with allyl or propargyl halides in the presence o~ magnesium metal to produce the desired allyl or propargyl derivatives.
Alternatively, the polyorganotin halides can be allowed to react with preformed allyl or propargyl mangesium halides. When a propargyl magnesium halide.

~22~ 9 is used, the resulting product is generally mixture of the propargyl and allenyl isomers.
~ he present organotin curing agents can be incorporated into the fluoroelastomer using conventional compounding techniques. The fluoroelastorner can also include the fillers, reinforcing agents, stabilizers, plasticizers, lubricants or processing aids typically used with elastomer compositions of this type. Carbon black is often added to such elastomeric compositions, acting as a filler, reinforcer, light screen and antioxidant. Another useful ingredient in formulations of the present invention is a cyclic polyether ("Crown") compound which reduces viscosity lS and improves processibility, such as those described in C. J. Pederson, J. Am. Chem. Soc. Vol 89, p 7017 (1967~.
The polymer and curing ayent, together with other components of the fluoroelasto~er composition, are mixed together by any convenient means, usually on a two-roll mill at a temperature of about from 40 to 100C. The mixed composition is shaped and cured or vulcanized by pressing it into a mold and heating at elevated temperatures. In general, the present compositions can be cured at temperatures lower than those considered necessary with curing agents previously used in the art. The optimum curing temperature will vary with the particular organotin compound used. In general, the present compositions can be effectively press cured at temperatures of about from 75 to 250C. However, compo~itions containing the tetraallyltin and tetrapropargyltin compounds can be precs cured at even lower temperatures, for example, as low as 25C. The 35 curing times at the higher temperatures which can be used are about from 5 to 30 minutes for a satisfactory press cure of a typical shaped article.
Longer curing times, up to several days, may be necessary for adequate cure at the lower ternperatures.
S In general, to attain the maximum physical properties in the cured elastomer, the elastomeric compositions, after press curing, are post-cured according to conventional techniques. Post-curing generally involves maintaining the press cured part - 10 at elevated temperatures under nitrogen for a period of several hours.
The composi~ions of the present invention provide excellent cured or vulcanized fluoroelastomer compositions which can be cured more rapidly and at lower temperatures than previous compositions containins curing agents such as tetraphenyltinO The present compositions also generally attain a more complete state of cuxe during the conventional press curing operation. Moreover, the cured compositions resulting from the present invention exhibit a surprising stability in a wide variety of environments, including unusual resistance to degradation by water often found in chemical processing and oil well operations. The compositions of the present invention provide outstanding cure performance when used in conjunction with fluoroelastomers containing secondary cure sites as exemplified by Nottke U.S. Patent 3,333,767. The curing of this type of elastomer has previously been unsatisfactory using the tetraphenyltin compositions previously known in the art.
The present invention is further illustrated by the following specific examples, in which parts and percentages are by weight unless otherwise 3s indicated.

In these E'xamples the perfluoroelastomer used was a terpolymer oE -tetraEluoroethylene, perfluoro(methylvinyl ether) and perfluoro(~-cyano-5-methyl-3,6-dioxa-1-octene) preparecl according to the procedures described in Breazeale, U.S. Pa-ten-t

4,281,092. The polymers contained 30 to 32 mole percent of the perfluoro(methylvinyl ether) and about 0.6 to 0.8 mole percent of the cyano monomer~ The polymers exhibited inherent viscosities ranging from 0.6 to 0.8 gl/g as measured in a solution containing 0.2 grams of polymer per 100 ml of solvent consisting of a 60/40/3 volume ratio of heptafluoro-2,3,3-trichlorobutane, perfluoro(butyltetrafluorohydrofuran) and ethylene glycol dimethylether.
Example 1 and Comparative Example A
Perfluoroelastomer was compounded on a two-roll rubber mill at 60DC with curing agent, carbon black and 18-crown-6 cyclic polyether (1, 4, 7, 10, 13, 16-hexaoxacylooctadecane) to reduce viscosity and improve processability.
The degree of crosslinking was measured in a Monsanto Oscillating Disc Rheometer* at 190DC. Test results are shown in Table I, and indicate that the present allyltin curing agents are significantly more active than tetraphenyltin, as shown by the higher delta torque valves of the ODR measurements.
The compound fluoroelastomers were pressed, cured and post curPd under the conditions reported in the table, and subsequently tested for physical pr~perties. The results are reported in Table I, and indicate that the compositions of the present invention are signiEicantly more resistant to exposure to hot water.

*denotes Trade mark.

` 3L;~2;~493 ~ABLE I
Exam~le __ _ Terpolymer 100 100 Allyltriphenyltin 2.8

5 Tetraphenyltin -- 3.0 18-Crown-6 0.3 0.3 SAF Black B 8 Minimum Torque (kg cm) 19.8 16.8 Tq 30 min. (kg cm) 2507 6.9 Tq 60 min. (kg cm)29.2 14.7 Tq 60 min. (kg cm)49.0 31.5 Press Cured Time (min)/Temp. C30~210 30/210 Post Cured (under nitrogen) lS Time (hr)/Temp. C6/90 6~90 10/90 to 305 10/90 to 316 Properties Tensile Test ~ASTM-D412 - Method A, Small dumbbells) 20 Stress at 100% Elong, MPa 4.2 3.2 Stress at break, MPa 14.8 13.5 Elongation at break, ~ 180 180 Compression Set ~70 hr/204C, ASTM D395, Yerzley Pellets) % 24 21 25 Water Resistance ~Three days liq~id water at 232 ~ 5C) Appearance Intact Swollen Volume Swell, Vol. % 2 241 1 Measured on a similar co~pound but with 12 phr SAF carbon black.

Ex_~ples 2-4 and Control Example B

~ The general procedure of Example 1 was repeated except tbat a white compound based on titanium oxide was prepared instead of a black 28~

compound. The compositions were tested as be:Fore anA
the results reported in Table II.
I~ these compositions were tested as with Example 1 and Comparative Example A, the compositions of the present invention would present a simil~r superiority in resistance to hot water.
TABLE II
Example B 2 3 4 Terpolymer 100 100 100 100 10 Diallyldibutyltin -- 3.02.0 2.0 `
Tetraphenyltin 4c0 - 2.0 2.0 18-Crown-6 -- -- 0.2 0.2 Sulfolane 0.6 0.6 Tio2 20 20 20 --1-5 Silica ~ 9 ODR (130C, Monsanto Oscillating Disc Rheometer) Minimum Torque (kg cm)18.7 12.610.7 20.2 Tq 30 min. (kg cm) 2.4 16.810.1 19.2 Tq 60 min. (kg cm) 5~7 17~9140 3 lg.3 Tq 60 min. (kg cm) 24.4 30.5 25.0 39.5 Press Cured Time (min)/Temp. C 30/210 30/210 30/210 30/210 Post Cured (under nitrogen) Time (hr~/Temp. C 6/25 to 204 18~2~4

6/~04 to 2~8 .

~L22~
g TABLE ~I (cont'd) Example _ 2 3 4_ Properties Tensile Test (ASTM-D412 - Method A, Small dumbbells, 5 ~5~) Stress at 100% Elong, MPa 2.9 2.7 2.5 4.2 Stress at break, MPa 10.2 11.3 7.5 8~4 Elongation at break, % 170 210 190 170 .-Compression Set (70 hr/204C, ASTM D395, #214 O-rings) % 65 46 49 60 Example 5 A semi-solid terpolymer was prepared from 97.1% hexafluoropropylene oxide, 2%
15 perfluoro~6,7-epoxy-4-oxaheptane nitrile~, and 0.9%
perfluoro(l,2-epoxy-10,11-epoxy-4,8-dioxaundecane).
A mixture of 13.7 g o~ this polymer and 0.22 ml tetrallyltin was stirred briefly under nitrogen at room temperature and then transferred to a slab 20 micromold which was pressed at 172 MPa. After three days at room temperature the well-formed slab was de~nolded, then post cured under nitrogen at 120C
overnight. A dumbbell cut ~rom the resulting soft, resilient elastomeric slab was tested and had the following ~ensile properties:
Stress at lO0~ Elong., MPa 0.34 Stress at 200% Elong~, MPa 0.55 Stress at 8reak, MPa 0.79 ~longation at Break, MPa 280%
30 Exam~le 6 The general procedure of Example l was repeated, except that the curing agent used was a mixture of allenyl- and propargyl- triphenyltin~ The curing agent was prepared according to the procedures 35 described in M. L. Quan ~ P. Cadiot, Bull. Soc. Chim.
Fr. 1965, pp 45-7.

~;~2~

The compounded fluoroelastomer was pressed, cured, post cured and tested as in Example 1, and the results are reported in Table III.
TABLE III
. . . _ .._ Terpolymer 100 Allenyl- and Propargyl triphenyltin 5.0 18-Crown-6 0.30 SAF Black 12 10 Minimum Torque (kg cm) 18.0 Tq 30 min. (kg cm) 23.4 Tq 60 min. (kg cm) 28.0 Tq 60 min. (kg cm) 46.0 ~ress Cured Time (min)/Temp. C 3~/210 Post Cured ~under nitrogen) Time (hr)/Temp. ~C 6/90 10~90 to 305 Properties Tensile Test (ASTM-D412 - Method A, Small dumbbells) Stress at 100~ Elong, MPa 1301 Stress at break, MPa 14~ 6 Elongation at break, % 110 Compression Set (70 hr/204C, AslrM D395, Yerzley Pellets) ~ 3

Claims

I Claim:

1. In a nitrile-substituted fluoroelastomer containing a curing agent, the improvement wherein the curing agent comprises about from 1 to 10 parts per 100 parts by weight of elastomer of an organotin compound having the general formula RxSnY4-x wherein x is 0-3, R is aryl of 6-10 carbon atoms or alkyl of 1-4 carbon atoms, and Y is at least one of allyl, propargyl, and allenyl.

2. A fluoroelastomer of Claim 1 wherein x is 3.

3. A fluoroelastomer composition of Claim 2 wherein R is aryl.

4. A fluoroelastomer composition of Claim 3 wherein R is phenyl.

5. A fluoroelastomer composition of Claim 1 wherein the fluoroelastomer is a terpolymer of tetrafluoroethylene, perfluoromethyl perfluorovinyl-ether and a cyano-substituted perfluorovinyl ether.

6. A fluoroelastomer composition of Claim 1 wherein the curing agent comprises about from 3 to S
parts per 100 parts of fluoroelastomer.

7. A fluoroelastomer composition of Claim 1 wherein Y is allyl.