CURABLE COMPOSITIONS AND METHOD OF USING SAME

Abstract: A curable composition that includes (a) at least one curable polymer comprising interpolymerized units derived from vinylidene fluoride; and (b) at least one cure accelerator comprising a silyl-functional onium salt, and a method for curing such compositions.

Description: CURABLE COMPOSITIONS AND METHOD OF USING SAME Background Fluoropolymers containing vinylidene fluoride units (e.g., copolymers of vinylidene fluoride and ethylenically unsaturated monomers such as hexafluoropropene) have particular utility in high temperature applications, including seals, gaskets, and linings, as described, for example, in Brullo, R.A., "Fluoroelastomer Rubber for Automotive Applications," Automotive Elastomer & Design. June 1985, "Fluoroelastomer Seal Up Automotive Future," Materials Engineering. October 1988, and "Fluorocarbon Elastomers," Encyclopedia of Polymer Science and Engineering, vol. 7, pp. 257 et seq. (2d ed., John Wiley & Sons, 1987). One reason is that such fluoropolymers, when cured, have good resistance to damage by heat, solvents, corrosive chemicals, and steam. However, the curing process is generally very slow, necessitating the use of a cure accelerator. A variety of organo-onium compounds have been proposed for this purpose. In addition, during the manufacturing process (particularly where injection molding is used) the cured polymers generally adhere to the surface ofthe mold. As a result, a shaped article prepared from the fluoropolymer is frequently torn or damaged when removed from the mold. Also, the incorporation of a mold release agent into the polymer can have serious adverse effects on the physical properties ofthe cured composition (e.g., Mooney Scorch, shrinkage, and compression set) which can limit the successful commercial use ofthe cured composition. Deposits of polymer on the mold cavity surface ("mold fouling") and poor release ofthe shaped, cured article from the mold are major reasons for defects, resulting in rejection ofthe article (which then adds to the expense of manufacturing such articles). One possible solution to the mold release problem is proposed in Kolb et al., U.S. 5,262,490 (which is hereby incorporated by references). Kolb describes compositions containing a phosphonium or ammonium salt, a sulfonium compound, and (optionally) a polyhydroxy compound that are designed to perform the dual functions of accelerating fluoropolymer cure and providing mold release properties. Summary In general, the invention features a new class of curable compositions that include (a) at least one curable polymer comprising interpolymerized units derived from vinylidene fluoride; and (b) at least one cure accelerator comprising a silyl-functional onium salt. In preferred embodiments, the cure accelerator has the formula where Q is an onium ion; A ' is a counterion; and R 1 , R 2 , R 3 , and R 4 , independently, are monovalent substituents in which at least one ofthe R 1 , R 2 , R 3 , and R 4 groups comprises a Ci-Cβ alkyl group (which may be a straight chain or branched, e.g., a methyl group) and at least one ofthe R 1 , R 2 , R 3 , and R 4 groups comprises a silyl group, with the proviso that when Q is a sulfonium ion, there is no R 4 group. Examples of preferred silyl groups include those having the formula -(CH 2 ) n -SiR 5 R 6 -(OSiR 7 R 8 ) y -Z or -(CH 2 ) n -Si-(OSiR 10 3 ) 3 or R 1 -(R 7 R 8 SiO) y -Si-(CH 2 ) n -Q + -R 2 A " , R 3 where Z is -OSiR 9 3 and each R 5 , R 6 , R 7 , R 8 , R 9 , and R 10 , independently, is a C*-C 6 alkyl group (which may be a straight chain or branched, e.g., a methyl group); n is 2-4; and y is 0-4. Preferably, at least one ofthe R 1 , R 2 , R 3 , and R 4 groups is an n-butyl, iso-butyl, aryl (e.g., phenyl), or alkaryl (e.g., benzyl) group, or combination thereof. Preferred onium ions include phosphonium, ammonium, and sulfonium ion, as well as combinations thereof, with phosphonium ions being particularly preferred. One example of a preferred composition features a cure accelerator having the formula (Me 3 SiO) 3 Si — (CH 2 ) 2 ≠ — ('— Bufc (2) CH 2 Ph A second example of a preferred composition features a cure accelerator having the formula A third example of a preferred composition features a cure accelerator having the formula A fourth example of a preferred composition features a cure accelerator having the formula A fifth example of a preferred composition features a cure accelerator having the formula A sixth example of a preferred composition features a cure accelerator having the formula A seventh example of a preferred composition features a cure accelerator having the formula [(Me 3 SiOSiMe 2 (CH 2 ) 3 ) 3 N + Me]A (8) An eighth example of a preferred composition features a cure accelerator having the formula The invention also features a method of curing a polymer comprising vinylidene fluoride units using the above-described cure accelerators. -A- As used herein: A "silyl group" is a group containing a silicon atom bonded to three organic substituents. A "silyl-functional onium salt" is an onium salt in which at least one of the substituents bonded to the onium ion comprises a silyl group. "Me" refers to a methyl group. "Ph" refers to a phenyl group. "Bu" refers to a butyl group, while "i-Bu" refers to an isobutyl group. The invention provides curable compositions in which cure time is decreased by means of a silyl-functional onium cure accelerator. In some cases, the silyl-functional onium cure accelerator itself may provide good mold release properties, thereby dispensing with the need for separate mold release agents. The resulting cured articles exhibit good physical properties. Other features and advantages ofthe invention will be apparent from the following description ofthe preferred embodiments thereof, and from the claims. Description ofthe Preferred Embodiments Curable vinylidene fluoride-containing fluoropolymer compositions according to the invention contain a silyl-functional onium salt as a cure accelerator. Examples of preferred accelerators have the structures set forth in the Summary of the Invention, above, in which the counterion A " may be an organic or inorganic anion, e.g., halide, thiosulfate, formate, cyanate, thiocyanate, tetraphenylborate, perchlorate, nitrate, tetrafluoroborate, hexafluorophosphate, oxalate, stearate, haloacetate, para-toluenesulphonate, ZnCl 4 2' , CdCl 2" , NiBr 4 2' , Hgl 3 " , sulfate, acetate, phosphate, phosphonate, hydroxide, alkoxide, phenoxide, trifluoromethane sulfonate, benzene sulfonate, hexachlorophosphate, hexachlorostannate, hexafluoroarsenate, hexafluoroantimonate, 2-mercaptobenzothiazolate, perfluoroalkanesulfonamido anion, bisphenoxide, or phenate. In cases where the counterion has a negative charge greater than one, a single counterion can be used for more than one onium compound. The R^R 10 groups, independently, are preferably selected from the group of radicals consisting of alkyl, aryl, and alkenyl radicals, or combinations thereof. The R groups can be unsubstituted or substituted with, e.g., chlorine, fluorine, bromine, cyano, -OR, and -COOR' moieties where R' is selected from the group of radicals consisting of Cι-C 2 n alkyl, aryl, aralkyl, and alkenyl radicals. In addition, any pair of R groups can be connected with each other and the onium ion to form a heterocyclic ring. The silyl-functional onium salts are generally prepared by one of two methods. The first method involves reacting, e.g., a phosphine, amine, or sulfide with a silylated alkylating agent (e.g., a silylated alkyl halide, aryl halide, or acyl halide), resulting in the expansion ofthe valence ofthe electron donating phosphorous, nitrogen, or sulfur atom and a positive charge on the organo-onium. Such reactions are well-known in the art. A general description of such reactions can be found in (a) Emmsley, J., "The Chemistry of Phosphorus," John Wiley and Sons, Inc., 1976 and (b) Carey, F.A. and Sundberg, R.J., "Advanced Organic Chemistry," Part B, 3rd Ed., Plenum Press, 1990. The second method involves preparing a silyl-containing phosphine, amine, or sulfide, followed by reaction with an alkyl or aryl halide such as benzyl chloride or allyl bromide. The silyl-containing compounds, in turn, are prepared via well-known reactions. For example, in the case of phosphines, the silyl-containing compounds are prepared via reaction of a phosphine with a vinyl silane as described, e.g., in Rahut et al., J. Ore. Chem.. 1961, 26, 5138; Pellon, J. Am. Chem. Soc. 1961, 83, 168; Buckler et al., J. Am. Chem. Soc. 1961, 83, 168; Langhans et al., Z. Naturforsch. 1990, 45b, 203; and Horvath et al., Science. 1994, 266, 72. In the case of amines, silylation involves reaction between a silane (e.g., pentamethyl disiloxane) and a vinyl or allyl amine (e.g., allyl amine) as described, e.g., in Colvin, E.W., "Silicon in Organic Synthesis," Ch. 21, Krieger Publishing Co., 1985 and Allcock et al., Organometallics. K), 3819 (1991). Examples of curable vinylidene fluoride-containing polymers are described in the aforementioned Kolb patent; Worm, U.S. 4,233,421; and Grootaert et al., U.S. 4,882,390, all of which are hereby incorporated by reference. Specific examples include copolymers and terpolymers of vinylidene fluoride with terminally unsaturated monoolefins typically used for the preparation of fluorine-containing polymers such as hexafluoropropene, chlorotrifluoroethylene, 2-chloropentafluoropropene, perfluoroalkyl vinyl ethers (e.g., CF 3 OCF=CF 2 or CF 3 CF 2 OCF=CF 2 ), tetrafluoroethylene, 1-hydropentafluoropropene, 2-hydropentafluoropropene, dichlorodifluoroethylene, trifluoroethylene, 1,1-dichlorofluoroethylene, vinyl fluoride, and mixtures thereof. Fluorine-free terminally unsaturated monoolefin monomers, e.g., ethylene or propylene, may also be used as co-monomers. Fillers are often added to the polymers discussed above to improve the physical properties ofthe cured composition or vulcanizate. When a filler is employed, it is added to the vulcanization recipe in amounts of up to about 100 parts per hundred parts by weight of polymer, preferably between about 1 and 50 parts per hundred parts by weight ofthe polymer. Examples of fillers which may be used are reinforcing thermal grade carbon blacks or non-black pigments of relatively low reinforcement characteristics such as clays, barytes, etc In some instances, it may also be desirable to add one or more diorgano sulfur oxide compounds, and other conventional adjuvants or ingredients, e.g., retarding agents and processing aids to the curable composition. The curable composition preferably contains a crosslinking agent as well. Such agents are well known and are described in the art, e.g., in the aforementioned Kolb and Worm patents, and in U.S. Pat. Nos. 4,259,463 (Moggi et al.), 3,876,654 (Pattison), and 5,384,374 (Guerra et al.), all of which are hereby incorporated by reference, and can include aromatic polyhydroxy compounds, aliphatic polyhydroxy compounds, and derivatives thereof. Blends may be used as well. Preferred polyhydroxy compounds are aromatic polyhydroxy compounds such as isopropylidene-bis(4-hydroxy-benzene) ("bisphenol A") and hexafluoroisopropylidenebis(4-hydroxybenzene) ("bisphenol AF"). Fluoroaliphatic sulfonamides can also be added, including those ofthe formula R f SO 2 NHR", where R" is a hydrogen atom or alkyl radical having, for example, from 1 to 20 carbon atoms, preferably from 1 to 12 carbon atoms, Rf is a fluoroaliphatic radical such as a perfluoroalkyl, e.g., C„F 2n+ ι where n is 1 to 20, or perfluorocycloalkyl, e.g., C n F 2n-1 where n is 3 to 20, such compounds being described, for example, in U.S. Pat. No. 5,086,123 (Guenther et al.). The fluoroaliphatic sulfonamide is preferably a perfluoroalkylsulfonamide and may be added as a separate compound, or as the anion ofthe organo-onium compound. The silyl onium cure accelerators and crosslinking agent can be added to the uncured polymer gum in the form of finely divided solids or as solutions in alcohol or ketone solvents by mixing the materials into the polymer gum stock. Thus mixed, the gum stock can generally be stored at room temperature for extended periods, e.g., up to two years or more. Prior to curing, an acid acceptor is mixed into the gum stock, after which storage life ofthe stock is more limited. Acid acceptors can be inorganic or organic. Organic acceptors include epoxies, sodium stearate, and magnesium oxalate. Examples of inorganic acceptors include magnesium oxide, lead oxide, calcium oxide, calcium hydroxide, dibasic lead phosphite, zinc oxide, barium carbonate, strontium hydroxide, calcium carbonate, etc. The preferred acid acceptors are magnesium oxide and calcium hydroxide. The acid acceptors can be used singly or in combination, and preferably are used in amounts ranging from about 2 to 25 parts per 100 parts by weight ofthe polymer. All ofthe components ofthe curing system may be admixed prior to their incorporation into the polymer gum without departing from the scope ofthe invention. The relative amounts ofthe crosslinking agent and silyl onium salt are present in the composition in such amounts as to provide the desired cure ofthe composition when mixed with acid acceptor. Representative proportions of components ofthe curing system are as follows: Acid acceptor: 0.5 to 40 phr Silyl onium : 0.2 to 5 mmhr Crosslinker : 0.3 to 10 mmhr All amounts are given in parts per 100 parts polymer (abbreviated "phr") or in millimoles per hundred grams polymer (abbreviated "mmhr"). These proportions are general ranges. The particular amount for each particular cure time and temperature will be apparent to one of ordinary skill in the art. In accordance with this invention, the desired amount of acid acceptor, silyl onium salt, crosslinking agent, diorgano sulfur oxide compounds (if any), and other conventional adjuvants or ingredients are added to the unvulcanized polymer (i.e. gum stock) and intimately admixed therewith or compounded by employing any ofthe usual rubber mixing devices such as Banbury mixers, roll mills, or any other convenient mixing device. For best results the temperature ofthe composition during mixing should not rise above about 120°C. During mixing it is necessary to distribute the components and adjuvants uniformly throughout the curable polymer. The curing process typically comprises molding the resulting composition under pressure at a temperature ranging from about 95°C to about 230°C, followed by curing. The composition of this invention is particularly useful for injection molding. The molded product is then usually post cured (e.g., oven cured) at a temperature between about 150°C and about 315°C, usually at about 232°C, for a period of from about 2 hours to 50 hours or more depending on the cross-sectional thickness ofthe sample. The invention will now be further described by way ofthe following examples. EXAMPLES The following examples illustrate curable compositions of this invention and advantages thereof, such as acceleration ofthe cure ofthe curable compositions and the added benefit of good mold release properties. Cure and rheological properties of several curable compositions were evaluated using the following test methods: Cure Rheology Tests were run on uncured, compounded admixtures using the Moving Die Rheometer (MDR) Model 2000E Monsanto at 177°C on an 8.0 g quantity ofthe admixture in accordance with ASTM D 5289-93a for a rotorless rheometer, no preheat, an oscillator frequency of 100 cpm and a 0.5° arc. Minimum torque (M L ), maximum torque (M H ), and delta torque (ΔT), the difference between M H and M L , were reported. Also reported were t s 2 (the time to a 2 unit rise in torque from M L ) t'50 (the time to increase torque above M L by 50% of delta torque), and t'90 (the time to increase torque above M L by 90% of delta torque), all of which were reported in minutes. Press-Cure data, unless otherwise noted, was obtained from 20 X 20 X 0.2cm sheets prepared by pressing a sample ofthe curable compositions at about 6.9 MPa for 12 min. at 177° C. Post-Cure data was obtained from sheets prepared as described above which were then further treated by heating the sheets in a circulating air oven maintained at about 232°C for 16 hours. Tensile Strength at Break, Elongation at Break and Stress at 100% Elongation were determined using a Syntech™ mechanical tester with a 200 lbs (88.9 kg) load cell in accordance with ASTM D 412-92 εl . Test specimen strips 5" x 0.5" x 0.125" (127 mm x 127 mm x 3.2 mm) were cut from the press- or post- cured sheets. A 2" (50.8 mm) gage section was used to follow the cross head displacement. All tests were run at a constant cross head displacement rate of 20 in./minute (508 mm/min.) in triplicate. The values reported were averages ofthe three tests. Stress at 100% Elongation, Elongation at Break, and Tensile Strength at Break were reported in units of Mega Pascals (MPa), %, and MPa respectively. Evaluations of injection molding performance, i.e. mold release, were performed using a DESMA 966.053 ZO lab injection molding machine available from Kloeckner Ferromatic Desma Gmbh of Germany. The machine is further described as having 500 kN mold closing force, 27kW total power installed, 55 mm injection piston diameter, 120 mm maximum piston stroke, 200 MPa maximum injection pressure, 400 mm/sec maximum injection speed and a plastication unit with 30 mm screw diameter and screw RPM of 30-220. The mold used to make O-rings was a 4 cavity mold with O-ring internal diameter of 48 mm, O-ring cross- section of 2.90 mm, a runner length of 13 mm, sprue base diameter of 5.2 mm, sprue length of 29 mm, and each cavity had a vacuum canal. The mold steel was STAVAX ESR with a surface finish EDM. The mold was conditioned before each experiment (change of formulation) by blasting the mold surface with 50-150 micron glass beads under 0.2 MPa pressure for 10 minutes. The mold was then conditioned for 30 minutes in a water-based caustic solution at 80°C and then ultrasonically cleaned in the solution for 10 minutes. After cleaning, the mold was rinsed with deionized water, dried and stored overnight before use. Multiple molding cycles were made of each formulation. The steady state O-ring injection molding conditions were 190°C mold temperature, 95°C injection barrel temperature, 60°C screw barrel temperature, injection speed 60% of maximum, after-injection pressure of 5.5 MPa for 2 seconds, screw RPM 35% of maximum, backpressure of 0.5 MPa, plastication delay of 2 seconds after end holding time and a vacuum time of 2.5 seconds. The holding time and heating time were both dependent upon vulcanization speed and were adjusted to obtain cured O-rings. The injection volume was adjusted to give similar flash to the parts molded. Experimental Preparation of Alkylsilyl Phosphines: The alkylsilyl phosphines used in the preparation of quaternary phosphonium salts used in the present invention were prepared via a free radical hydrophosphorylation reaction, as described below. Several halides and an amine used in the salt preparations were also synthesized as described below. The reactions were carried out at room temperature and pressures unless otherwise noted. Structural characterization data were obtained by NMR and IR spectroscopic techniques. Phosphine A: 2-((tris-trimethylsiloxy)silyl)ethyl di-isobutylphosphine (Phosphine A) was prepared by the interaction between vinyl tris(trimethylsiloxy) silane and di-isobutylphosphine (DIBP) in toluene, as follows. A 1 L, four-neck flask, equipped with an overhead stirrer, a condenser, nitrogen purge, thermometer and rubber septum, was charged with 120 g (0.82 mol) of di-isobutyl phosphine, available from Cytec Industries, Inc. as a 70% solution in toluene. The flask assembly was placed on an adjustable lab jack so that either external heating or cooling ofthe reaction flask could be done. Additional toluene was added to dilute the DIBP solution to about 50% solids. The reaction vessel was purged with nitrogen for fifteen minutes and a positive stream of nitrogen was maintained throughout the reaction to minimize the oxidation ofthe DIBP. In a second flask, 270 g (0.84 mol) of vinyl tris(trimethylsiloxy)silane (available from Hϋls America Inc.) was mixed with about 100 ml of toluene and 1.3 g (8.5 mmol) of azobisisobutyronitrile (AIBN), available from Aldrich Chemical Company, Inc. The toluene solution of DIBP in the four-neck flask was warmed to about 80°C and the vinyl silane solution from the second flask was added via a syringe pump to the warm DIBP at about 2.5 mL/min. After about 20 min., a noticeable exotherm was detected, and the rate of silane addition and external heating were adjusted so that a temperature of 80° to 95°C could be maintained. After complete addition ofthe vinyl silane solution, the reaction mixture temperature was controlled at about 85°C for an additional 2 hrs to ensure complete consumption ofthe DIBP had occurred. When the reaction was complete as determined by 31 P NMR spectroscopy, (δ = - 40 ppm up field from external H 3 PO ), the toluene solvent was removed under reduced pressure. The desired product 2-((tris trimethylsiloxy)silyl) ethyl di-isobutylphosphine was obtained in yields of 70% to 80%. 1H, 31 P NMR spectroscopy confirmed the structure ofthe desired product. Phosphine B: l,3-(2-ethyl di-isobutylphosphine) tetramethyldisiloxane (Phosphine B) was prepared in a manner similar to Phosphine A, except 78 g (0.42 mol) of 1,3-divinyl tetramethyl disiloxane, available from Hϋls America Inc., was used instead ofthe 270 g (0.84 mol) of vinyl tris(trimethylsiloxy)silane. Halide C: 3-(2-pentamethyldisiloxy ethyl) benzylchloride (Halide C) was prepared in a 500 ml reaction vessel equipped with a magnetic stir bar, reflux condenser and a nitrogen inlet by charging 200 mL of tetrahydrofuran (THF), 40.0 g (0.27 mol) pentamethyldisiloxane, available from Hϋls-America, 43.5 g (0.289 mol) 3 -vinylbenzyl chloride (VBC), available from Aldrich Chemical Company, Inc, and 0.2 g (1%) w/w) of a platinum hydrosilylation catalyst (1,3-divinyltetramethyl disiloxane platinum (DVDS-Pt), available from Hϋls-America) to the vessel. The progress ofthe reaction was monitored by IR spectroscopy to follow disappearance ofthe Si-H stretch at 2100 cm "1 . After 12 hrs at 25°C, the reaction was found to be complete by IR analysis. The THF solvent was removed by rotoevaporation. The desired product was isolated by distillation, b.p. 110-115°C at 0.15 mmHg and 65.23 g (78% yield) 74% α isomer, 26% β isomer was collected. Halide D: 3-(2-heptamethyltrisiloxy ethyl) benzylchloride (Halide D) was prepared in a manner similar to Halide C, except 20.3 g (0.13 mol) of VBC and 28.8 g (0.13 mol) heptamethyl trisiloxane (available from Hϋls-America) were used instead of the pentamethyldisiloxane. After 12 hrs at 25°C, the reaction was found to be complete by IR analysis. The THF solvent was removed by rotoevaporation to produce 48.2 g of a light brown crude product. The product was purified by distillation at 115-125°C at 0.1 mm Hg. The yield was 40.5 g (83% yield). Analysis by 1H and 13 C NMR spectroscopy confirmed the formation ofthe desired product. It was found to contain 66% α isomer and 34% β isomer addition product. Halide E: 3-(2-tris(trimethylsiloxy)silylethyl) benzylchloride (Halide E) was prepared in a manner similar to Halide C, except that 30.5 g (0.103 mol) tris- trimethylsiloxy silane, available from Hϋls America Inc., was reacted with 18.0 g (0.11 mol) VBC. The desired product was isolated by distillation, b.p. >185°C at 0.15 mmHg and 32.5 g of >98% α isomer, <2% β isomer was collected. Halide F: l,5-bis(2-ethyl-3-benzylchloro)hexamethyltrisiloxane (Halide F) was prepared in a manner similar to Halide C, except that the reaction was done at 100% solids using 25.0 g (0.12 mol) of 1,5 -hexamethyl trisiloxane, available from Hϋls America Inc., and 38.9 g (0.252 mol) VBC. The yield was 34.79 g, isolated by distillation, b.p. 195°-210°C. at 0.1 mmHg. In addition to NMR analysis, C,H,N analysis confirmed the structure ofthe desired product. Analysis for C 24 H 38 Cl 2 O 2 Si 3 , Calc'd: C, 56.08%; H, 7.47%; N, 0% Found: C, 56.1%; H, 7.3%; N, < 0.1%. Amine G: Tris-N,N,N-(3 -propyl pentamethyl disiloxane)amine (Amine G) was prepared under an atmosphere of nitrogen in a 250-ml, 3-neck, round-bottomed flask, equipped with a magnetic stir bar, a reflux condenser and an addition funnel. This flask was charged with 15.9 g (115.6 mmol) of triallylamine, (CH 2 =CHCH 2 ) 3 N, available from Aldrich Chemical Company, Inc., and 50 ml of heptane. About 1 to 2 wt% of DVDS-Pt was added to the mixture and the mixture was heated to 65-70°C. The addition funnel was charged with a solution of 50.0 g (340 mmol) Me 3 SiOSiMe 2 H, available from Hϋls America Inc., in 50 ml of heptane, which was then added to the reaction mixture dropwise with stirring. After the addition was complete, the reaction mixture was observed to be brownish in color. An IR spectrum showed the disappearance ofthe Si-H band at 2160 cm '1 . After an additional 3 hrs. of stirring, some colloidal clay was added to the mixture to adsorb the catalyst. The mixture was then allowed to cool down to room temperature and was stirred overnight. The reaction mixture was filtered, and the heptane was separated on a rotary evaporator. The product was Kugelrhor distilled at 120-160°C at 1.7 mm Hg yielding a yellowish, slightly viscous fluid (56.5 g, 86 %). The 1H, 13 C and 29 Si NMR spectra were consistent with the structure ofthe desired product. Onium H Onium H was prepared in a one-neck, airless flask by charging 30 g (0.064 mol) of 2-((tris trimethylsiloxy)silyl)ethyl di-isobutylphosphine (Phosphine A) and sufficient isopropanol to form a 50% solids solution. A positive flow of nitrogen was maintained through out the reaction. Then, 8.2 g (0.065 mol) of benzyl chloride, available from Aldrich Chemical Company, Inc., was added to the phosphine solution. The reaction mixture was warmed to about 45°C and allowed to react for 16 hrs. The progress ofthe quaternization reaction was monitored by 31 P NMR spectroscopy. The reaction was considered complete when the 1 P NMR spectrum ofthe reaction mixture consisted of a major singlet at +30 ppm. The reaction product was isolated by solvent removal under reduced pressure. Care was taken to avoid heating the product above 65°C. The product was isolated as a waxy, white solid . Characterization ofthe product by 31 P, l NMR spectroscopy confirmed the formation ofthe desired compound. The silyl phosphonium product contained a small percentage of phosphine oxide. No attempt was made to remove this by-product from the desired phosphonium product. Onium I: Onium I was prepared in a manner similar to Onium H except Phosphine B was used instead of Phosphine A. Oniu s J - M: Onium J was prepared in a 500 ml round bottom flask by charging 15.0 g (0.05 mol) of 3-(2-pentamethyl disiloxy ethyl) benzylchloride (Halide C) and 150 g of 2-propanol. After the solids were dissolved, 11.0 g, (0.05 mol) of tri-n-butylphosphine, available from Aldrich Chemical Company, Inc., was added to this solution. The reaction temperature was kept to less than 50°C. The progress ofthe reaction was monitored by 31 P NMR spectroscopy. After 12 hrs, the phosphine was quantitatively converted to the phosphonium, ( 31 P NMR spectrum consisted of a singlet at δ = +30 ppm). The alkylsilylphosphonium was isolated by solvent removal under reduced pressure at 50°C. The product, 3-(2-pentamethyldisiloxy ethyl) tributyl benzyl phosphonium chloride, was isolated as a white, waxy solid. Oniums K, L, and M were prepared in a manner similar to Onium J except Halides D, E, and F, respectively, were used instead of Halide C. In all cases the alkylsilyl phosphoniums were isolated as low melting, waxy solids. 1H and 31 P NMR spectroscopy were utilized to confirm the structure and purity ofthe final product. Onium N: N,N,N-tris(3 -propyl pentamethyldisiloxy)-N-methyl ammonium iodide (Onium N) was prepared in a 500-ml 2-necked round-bottomed flask equipped with a magnetic stir bar and fitted with an addition funnel. The flask was charged with 29.3 g (207.2 mmol) CH 3 I, available from Aldrich Chemical Company, Inc., and 170 ml of acetone. The reaction flask was cooled in an ice/water bath to about 10- 20°C. Note: The product of this reaction is sensitive to temperatures above 50°C so the temperature ofthe reaction mixture was kept below 50°C through the workup ofthe product. The addition funnel was charged with a solution of 30.0 g (51.8 mmol) of (Me 3 SiOSiMe 2 (CH 2 ) 3 ) 3 N, prepared above as Amine G, in 100 ml of acetone. This solution was added very slowly dropwise to the reaction mixture with stirring overnight. The acetone and excess CH 3 I were removed under reduced atmosphere yielding 35.8 g of a brownish red viscous material. The 1H, 13 C and 29 Si NMR spectra were consistent with the structure ofthe desired product (76% active). The major side product of this reaction was the formation of (Me 3 SiOSiMe 2 (CH 2 ) 3 ) 2 NMe 2 I-. Examples 1-9: The following examples illustrate the use of organo-onium vulcanization accelerators in the curable compositions ofthe invention. The ingredients used in each composition were compounded on a two roll mill using standard methods. The organo-onium vulcanization accelerators were prepared as described above. Example 1: In Example 1, a curable composition ofthe invention was prepared on a two-roll mill by mixing a master batch of 1000 g of a fluorine-containing copolymer of vinylidene fluoride (60 wt%) and hexafluoropropylene (40 wt%), available from 3M Co. as Fluorel™ Fluoroelastomer FC-2230, 60 g of Ca(OH) 2 , 30 g of MgO, and 40 g of Viton™ Curative #30, available from E. I. DuPont de Nemours and Co. A 113 g sample of this master batch was further mixed on a two-roll mill with a 50% solids solution in methanol of 1.7 mmol of Onium H and 30 g of MT- N990 carbon black. The cure ofthe resulting mixture was analyzed on an 8.0 g sample ofthe mixture using a Monsanto moving die rheometer (MDR) at 177°C. A press cured sheet was prepared by pressing at 177°C and 6.9 MPa for 12 min. The press-cured sheet easily demolded from the mold without the use of forced air. A sample ofthe press-cured sheet was post-cured in air at about 232°C for 16 hr. Physical property testing was performed on press-cured and post-cured sheets. The final formulation ofthe compounded gum was such that the sample contained the components and amounts as shown in Table 1. Table 1 Fluoroelastomer 100 phr Viton™ Curative #30' 4 phr Onium H 1.7 mmhr Ca(OH) 2 6 phr MgO 3 phr Thermax™-N990 carbon black 30 phr Contains 50% wt active bisphenol AF, 6 mmol. Example 2-6: In Examples 2-6, samples of curable compositions according to the invention were prepared and evaluated in a manner similar to Example 1 using 113 g samples ofthe master batch prepared in Example 1 except the alkylsilyl oniums used were as shown in Table 2. Table 2 Example Alkylsilyl onium 2 Onium I 3 Onium J 4 Onium K 5 Onium L 6 Onium M Comparative Example Cl: In Comparative Example Cl, a sample of a curable composition was prepared as in Example 1 except the alkylsilyl onium was replaced by 0.5 g (1.30 mmol) of triphenyl benzylphosphonium chloride, available from Aldrich Chemical Company, Inc. Onium O: Onium O, an alkylsilyl ammonium cure accelerator, was prepared in a 10 ml flask by reacting 0.44 g (1.3 mmol) of bisphenol- AF, with 0.28 g (1.3 mmol) of sodium methoxide (in a 25 wt % solution in methanol), both available from Aldrich Chemical Company, Inc. Next, 0.94 g (1.3 mmol) ofthe alkylsilyl methyl ammonium iodide prepared as Onium N was added, and the resulting mixture used directly without further purification to prepare a curable composition as described in Example 7. Example 7: A curable composition ofthe invention was prepared in a manner similar to Example 1 except 1.3 mmol of Onium O (prepared as described above) was substituted for the 1.7 mmol of Onium H. The cure and rheological properties obtained are listed in Table 3. The torque values are reported in deci Newton metres (dN*>m) Table 3 Torque Example ML M H ΔT ts2 t'50 t'90 (dN » m) (dNun) (dN « m) (min) (min) (min) Cl 0.97 27.12 26.15 1.30 1.58 2.29 1 1.03 20.57 19.55 1.08 1.67 2.42 2 1.19 29.38 28.19 1.91 2.40 3.47 3 0.97 30.85 29.89 1.22 1.5 2.29 4 1.05 31.30 30.30 1.47 1.83 2.79 5 1.02 32.77 31.79 1.37 1.75 2.73 6 1.19 24.07 22.93 1.67 2.13 3.43 7 0.86 24.07 23.18 5.49 9.84 25.0 The results in Table 3 show that all compositions ofthe invention will result in a cured fluoroelastomer article. Physical properties were measured on press-cured sheets (177°C, 12 minutes) and post-cured sheets (232°C, 16 hrs). The results are listed below in Tables 4 and 5. Table 4: Press-Cured Sheet Mechanical Property Data Example Stress at Elongation Tensile 100% Elong. at Break Strength (MPa) (%) (MPa) Cl 4.7 268 10.7 1 3.9 292 8.8 2 4.9 246 9.8 3 5.0 239 10.4 4 4.9 226 9.7 5 4.7 235 9.3 6 3.8 316 9.9 7 3.5 237 7.0 The results in Table 4 show that the curable compositions of this invention provide cured articles with acceptable initial cure properties. Table 5: Post-Cure Sheet Mechanical Property Data Example Stress at Eloi tion Tensile 100% Elong. at B k Strength (MPa) (%) (MPa) Cl 5.8 218 13.3 1 5.7 219 13.5 2 6.9 191 13.0 3 6.9 190 13.5 4 6.6 194 12.6 5 6.6 204 13.8 6 5.1 237 12.6 7 6.6 191 10.4 The results in Table 5 show the curable compositions of this invention provide cured articles with acceptable post cure properties. Compression set data were obtained using ASTM method D-395-89. O-rings were press cured for 12 min. at 177°C and post cured for 16 hrs at 232°C. O-rings were compressed 25% for 70 hrs at 200°C. Data (shown in Table 6) are reported as percent ofthe compression remaining after the tests. Table 6 Example # Comp set Cl 18.2 1 29.3 2 35.1 3 24.0 4 25.0 5 26.4 6 24.0 7 29.0 The results in Table 6 show the curable compositions of this invention provide cured articles with acceptable compression set properties. Example 8 and Comparative Example C2: A sample was prepared according to the procedure set forth in Example 1 except that 0.75 phr camauba wax (available from Aldrich Chemical Co.) was added to the formulation as well. Comparative Example C2 was prepared according to the procedure set forth in Example Cl except that 0.75 phr camauba wax (available from Aldrich Chemical Co.) was added to the formulation as well. Injection molding evaluations were performed as described above and evaluated with the following rating system ranging from a rating of 0 (worst release) to a rating of 8 (best release) which is described below. The results ofthe evaluation are presented in Table 7. A release rating of 0 was given: When no parts could be removed from the mold by any means without tearing them and this was observed for each molding cycle. The molded parts may or may not have torn when the mold was opened. Everything including runners and flash stuck strongly to the mold surface and was difficult to remove. Rubbing with copper wool or similar was needed to remove any stuck flash or molded goods from the mold surface. A release rating of 1 was given: When only some ofthe parts could be removed in one piece, although with great difficulty even when demolding was assisted with an air gun. The molded parts may or may not have torn when the mold was opened. Everything including runners and flash stuck strongly to the mold surface and was difficult to remove. Rubbing with copper wool or similar was needed to remove any stuck flash or molded goods from the mold surface. A release rating of 2 was given: When most ofthe parts could be removed in one piece, although with great difficulty even when demolding is assisted with an air gun. Everything including runners and flash stuck strongly to the mold surface and was difficult to remove. Rubbing with copper wool or similar was needed to remove any stuck flash or molded goods from the mold surface. Air alone was not enough to demold the stuck parts or flash. A release rating of 3 was given: When nearly all parts could be removed in one piece, only with the assistance of an air gun. The runners and some flash could be removed with the air gun but not with out tearing. The remaining flash that stuck to the mold required rubbing with fabric to remove it from the mold. Air alone was not enough. A release rating of 4 was given: When all parts could be removed in one piece, only with the assistance of an air gun. The runners could be removed without tearing but not in one piece with the parts, not even when assisted with an air gun. A lot of flash tore and stuck to the mold and required rubbing with fabric to remove it from the mold. Air alone was not enough. A release rating of 5 was given: When all parts and runner system could be removed without tearing but only with the assistance of an air gun. Some flash tore and stuck to the mold and required rubbing with fabric to remove it from the mold. Air alone was not enough to remove flash that remained stuck to the mold surface. A release rating of 6 was given: When nearly all parts and runner system could be removed without tearing but only with the assistance of an air gun. Flash seldom tore and stuck to the mold. When some flash did stick to the mold, light rubbing or a short blast from the air gun easily removed the flash. A release rating of 7 was given: When all shots, parts, runner system and flash could be removed without tearing but only minimal assistance of an air gun was used. Occasional demolding without air and tearing was possible. A release rating of 8 was given: When all parts, runners and flash could be consistently removed without tearing and without using air. Demolding by hand and with very low forces was all that was required to removed all parts, runners and flash. Table 7 - M old Release Example Mold Release Ratine C2 5 8 8 Example 9: A sample was prepared according to the procedure set forth in Example 5 except that the fluoropolymer was a copolymer comprising 60 wt.% vinylidene fluoride and 40 wt.% hexafluoropropene with a total fluorine content of 66 wt.%. The copolymer was prepared according to the method described in Example 3 of Grootaert et al., U.S. Pat. No. 5,285,002, hereby incorporated by reference. In addition, 4,4'-(hexafluoroisopropylidene) diphenol (3.0 g, 2.1 mmhr, commercially available as Bisphenol-AF from Aldrich Chemical Co.) in 70 wt.% ethanol solution was used in place of Viton™ Curative-30. Injection molding evaluations were carried out and mold release was evaluated and rated in accordance with the rating system described in Example 8 and Comparative Example C2. The mold release ratio for the comparison was a 4. Other embodiments are within the following claims.

Claims: What is claimed is: 1. A curable composition comprising: (a) at least one curable polymer comprising interpolymerized units derived from vinylidene fluoride; and (b) at least one cure accelerator comprising a silyl-functional onium salt. 2. A method of curing a polymer comprising interpolymerized units derived from vinylidene fluoride comprising combining said polymer with a cure accelerator comprising a silylated onium salt under reaction conditions sufficient to cure said polymer. 3. A composition according to claim 1 or 2 comprising a cure accelerator having the formula where Q is an onium ion; A ' is a counterion; and R 1 , R 2 , R 3 , and R 4 , independently, are monovalent substituents in which at least one of said R 1 , R 2 , R 3 , and R 4 groups comprises a Ci-Cβ alkyl group and at least one of said R 1 , R 2 , R 3 , and R 4 groups comprises a silyl group, with the proviso that when Q is a sulfonium ion, there is no R 4 group. 4. A composition according to claim 3 wherein said silyl group has the formula -(CH 2 )„-SiR 5 R 6 -(OSiR 7 R 8 ) y -Z or -(CH 2 ) n -Si-(OSiR 10 3 ) 3 or R 1 I -(R 7 R 8 SiO) y -Si-(CH 2 ) n -Q + -R 2 A " , R 3 where Z is -OSiR 9 3 and each R 5 , R 6 , R 7 , R 8 , R 9 , and R 10 , independently, is a C--C 6 alkyl group; n is 2-4; and y is 0-4. 5. A composition according to claim 3 or 4 wherein at least one of said R 1 , R 2 , R 3 , and R 4 groups is an n-butyl or iso-butyl group. 6. A composition according to claim 3, 4, or 5 wherein at least one of said R 1 , R 2 , R 3 , and R 4 groups comprises an aryl or alkaryl group. 7. A composition according to any one of claims 1-6 wherein the onium ion comprises a phosphonium, ammonium, or sulfonium ion.

Inventors: ARREN DIRK H C, COGGIO WILLIAM D, PARKER DOUGLAS S, ARREN, DIRK, H., C., COGGIO, WILLIAM, D., PARKER, DOUGLAS, S.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: C08K5
IPC codes: C08K5, C08L27