The present invention concerns the synthesis of new fluoro elastomers having very low glass transition temperatures (Tg), with a good resistance to acids, oil and fuels, along with good workability properties. The elastomers of this invention contain hexafluoropropene (HFP), perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSO2F), and vinylidene fluoride (VDF) and/or perfluoro vinyl ether and/or a fluoro alkene. These elastomers are prepared by radical copolymerisation of HFP with PFSO2F or radical terpolymerisation of HFP with PFSO2F and VDF in the presence of different conventional organic initiators, such as the peroxides, the peresters, the diazo compounds or the alkyl peroxypivalates.
Fluorinated elastomers offer a unique combination of extremely advantageous properties. Among these, are their thermal resistance, to oxidation, by ultraviolet rays (UV), to the degradation due to ageing, corrosive chemical agents and fuels. They possess, among other things, low surface tensions, dielectric constants and refractive indexes. In addition, they resist the absorption of water. All these properties make them materials of choice in diverse applications of high technology such as components of fuel cells, seals in the aeronautical field, semiconductors in microelectronics, hoses, pipes, pump casings and diaphragms in the chemical, automotive and petroleum industries.
However, hexafluoropropene (HFP) elastomers are not numerous. Despite the fact that commercial elastomers such as Fluorel®, FKM®, Technoflon®, Viton®A or Viton®B (VDF/HFP or VDF/HFP/TFE) offer good chemical and thermal resistances, their glass transition temperatures (Tg) are not sufficiently low. The Tg of the aforementioned products generally vary between −10 and −25° C. The lowest value found in the literature is that that of Viton®B, whose Tg is −26° C., which is surprising because the manufacturer claims a Tg varying between −5 and −15° C. for this product. To compete with these elastomers, the company Ausimont offers a copolymer VDF/pentafluoropropene (Technoflon®) resistant to flames and oxidation, but not having a Tg lower than −26° C. and consequently the comonomer is difficult to obtain.
It is well known that copolymers containing HFP with tetrafluoroethylene (TFE) are thermoplastics, while the introduction of another fluorinated monomer such as, for example, trifluorovinyl ethers bring about the elastomeric character. DuPont has suggested a new generation of elastomers based on perfluoroalkyl vinyl ether (PAVE) but which do not contain HFP, and which are resistant to low temperatures, thus copolymers have been produced, such as the copolymers of tetrafluoroethylene (TFE)/perfluoromethyl vinyl ether (PMVE) (Kalrez®), of which the Tg do not go below −15° C., the TFE/PMVE described in EP 0 077 998, of which the Tg are −9° C., or TFE/perfluoroalkylvinylether (PAVE) described in U.S. Pat. No. 4,948,853. But it is mainly the terpolymers which offer even lower Tg's. Among them, we note the terpolymer TFE/ethylene/PMVE of which the Tg is −17° C., or the terpolymer TFE/VDF/PAVE (described in EP 0 131 308), and especially the terpolymer TFE/VDF/PMVE (Viton GLT®) where the Tg is −33° C.
Moreover, elastomers containing TFE/PAVE/VDF, used as O-rings give very good resistance to polar solvents (EP 0 618 241, Ausimont and Japanese Patent-A-3066714 Chem. Abstr., 115:73436z).
The terpolymerisation of TFE with PMVE and F2C═CF[OCF2CF(CF3)]nOC3F7 (Polym. J., 1985, 17, 253) conferred to the elastomers a Tg (of −9 to −76° C.) and is dependant on the value of the subscript n in the HFPO and to the percentage of the two oxygenated comonomers.
DuPont has also moreover produced Nafion® membranes by the copolymerisation of TFE with F2C═CFOCF2CF(CF3)OC2F4SO2F(PFSO2F). In addition, Asahi Glass uses the same sulfonated monomer for the fabrication of Flemion® membranes. Other monomers with the same functionality are, for example F2C═CFOCF2CF(CF3)OC3F6SO2F (for Aciplex® membranes, by Asahi Chemical), or CF2═CFOC2F4SO2F, where the functionality is a carboxylated F2C═CFO[CF2CF(CF3)O]xC2F4CO2CH3 (for Nafion® membranes or Aciplex® where x equals 1 and for Flemion® membranes if x equals 0) are also used.
The copolymerisation of HFP with other fluorinated olefins is well known, but the olefins used are PAVE, which are essentially perfluoromethyl vinyl ether (PMVE) or 2-bromoperfluoroethyl perfluorovinyl ether as cited in patents EP 410 351 and CA 2,182,328.
Moreover, EP 0 525 685 describes the synthesis of terpolymers HFP/PMVE/VDF leading to elastomers having a Tg equal to −27° C. (the lowest possible value) contrary to copolymers VDF/HFP where the Tg is −23° C. In WO 9220743 which describes the synthesis of terpolymers VDF/HFP/F2C═CFO(CF2)nCF3 (where n varies between 0 and 5) obtained in the presence of a transfer agent (1,4-diiodoperfluorobutane), subsequently reticulated with peroxides.
It is especially the tetrapolymers containing TFE, VDF, HFP and PAVE which were produced. For example, DE 2,457,102 describes the preparation of tetrapolymers HFP/PMVE/TFE/VDF by emulsion copolymerisation. EP 0 525 687 relates to the synthesis of polymers HFP/PAVE/VDF/TFE presenting good chemical resistance and good workability (for example, for molding). Analogous properties have been seen in tetrapolymers containing HFP/PAVE/VDF and olefines having 2 to 4 carbon atoms (see EP 0 570 762). Moreover, CA 2,068,754 gives the state of pentapolymers HFP/VDF/TFE/PMVE/ethylene of which the Tg varies between −9 and −18° C., and as low as −28° C. when the monomer F2C═CFOC2F4Br also participates in this polymerisation (hexapolymerisation). By the same token, the reticulated polymers containing HFP, VDF, TFE and precipitated brominated monomer have been described in EP 0 410 351 and in CA 2,182,328 or in articles Rubber Chem. Technology, 1982, 55, 1004 and Kautsch. Gummi Kunstst., 1991, 44, 833.
The addition of a non conjugated diene H2C═CHC4F8CH═CH2 in the preceding polymerisations favours the reticulation of these elastomers, as indicated in DE 4,137,967 and EP 0 769 521.
In addition, U.S. Pat. No. 3,282,875 concerns the terpolymers containing HFP, VDF and PFSO2F but containing a very low proportion of sulfonated monomer, between 1 and 2%. It is important to know that the concentration of PFSO2F in the polymers was determined by elemental analysis. Moreover, the Tg of the terpolymers is not mentioned.
Finally, the polymerisation containing HFP, PMVE and other fluorinated alkenes was conducted in supercritical CO2 medium (U.S. Pat. No. 5,674,957).
It would thus be desirable to develop new elastomers having a very low glass transition temperature and obtained using inexpensive comonomers such as HFP. These elastomers would preferably be obtained through a simple process not requiring dangerous experimental conditions.
The present invention consists of fluorinated elastomers comprising neither tetrafluoroethylene (TFE), nor monomers containing siloxane groups, and having glass transition temperatures (Tg) between −36 and −50° C. and comprising hexafluoropropene (HFP) monomer and a comonomer of perfluorosulfonyl ethoxy propyl vinyl ether fluoride (PSEPVE) or perfluoro (4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSO2F).
The fluorinated elastomers according to this invention can also comprise vinylidene fluoride (VDF) and/or fluorinated alkenes and/or vinyl perfluorinated ethers.
Another object of the invention is to learn in a precise non-ambiguous manner the composition of the copolymers according to the invention, i.e. the molar percentages of each of the comonomers present in the copolymers and the terpolymers.
In a preferred embodiment, the elastomer contains less than 50 mole % of HFP, and preferably between 10 and 35 mole %, 15 to 80 mole % of PFSO2F, and between 0 and 75 mole % of VDF and/or fluorinated alkenes and/or vinyl perfluorinated ethers.
The invention also concerns a process for the preparation of fluorinated elastomers by copolymerisation of hexafluoropropene (HFP) with perfluorosulfonyl ethoxy propyl vinyl ether fluoride (PSEPVE) or perfluoro (4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSO2F), characterised with a preparation through radical copolymerisation in the presence of an organic initiator and at a temperature between 20 and 200° C., for a period of approximately 2 and 6 hours, and an initial pressure between 2 and 100 bars, with the said pressure allowed to fall progressively while the monomers are consumed.
In view of the prior art, HFP was chosen for the preparation of elastomers according to this invention, because it was less expensive and more workable than TFE. Being less expensive, it can be used in larger quantities in the copolymer, and can be comprised of a second monomer perfluorosulfonyl ethoxy propyl vinyl ether fluoride (PSEPVE) or the perfluoro (4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSO2F). The use of HFP confers on the polymers formed improved elastomeric character and improved resistance to chemical agents, petroleum, and to oxidation.
The present invention also comprises terpolymers where the third comonomer is preferably VDF, this monomer leads to a low Tg, being inexpensive and easily workable, copolymerised (reactive) with free radicals; the PVDF groups in the polymer bring extra chemical and thermal inertia as well as better resistance to ageing.
The present invention preferably concerns the synthesis of novel fluorinated copolymer elastomers, containing hexafluoropropene and perfluorosulfonyl ethoxy propyl vinyl ether fluoride or perfluoro (4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride, and possibly other fluorinated alkenes, and/or vinylidene fluoride and/or vinyl perfluorinated ethers. Among the advantages of the present invention:
The field of the present invention extends to all types of general process uses: emulsion, miniemulsion, microemulsion, mass, suspension, microsuspension and solution polymerisation. All can be used according to their conventional means, but solution polymerisation was used preferentially, uniquely for reasons of simplifying laboratory operations, because in the case of solution polymerisation, the operating pressures are fairly low, in the order of 20 to 40 bars. In the case of emulsion, mass and suspension polymerisation, the operating pressure is higher, in the order of 40 to 100 bars.
The various fluorinated alkenes employed contain more than four carbon atoms and have the following structure R1R2C═CR3R4 where at least one of the substituents R1-4 are fluorinated or perfluorinated. This encompases: vinyl fluoride (VF), vinylidene fluoride (VDF), trifluoroethylene (TFE), chlorotrifluoroethylene (CTFE), bromotrifluoroethylene, 1-hydropentafluoropropylene, hexafluoroisobutylene, 3,3,3-trifluoropropene, 1,2-dichlorodifluoroethylene, 2-chloro-1,1-difluoroethylene, 1,2-difluoroethylene, 1,1-difluorodichloroethylene and generally all vinyl fluorinated and perfluorinated compounds. In addition, these perfluorinated vinyl ethers can also play a role as comonomers. Among these vinyl ethers, we can cite the perfluoroalkyl vinyl ethers (PAVE) where the alkyl group has between one and three carbon atoms: for example, perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether (PEVE) and perfluoropropyl vinyl ether (PPVE). These monomers can also be perfluoroalkoxy alkyl vinyl ethers (PAAVE), described in U.S. Pat. No. 3,291,843 and in the review Prog. Polym. Sci., M. Yamabe et coll., 1986, 12, 229 and A. L. Logothetis, 1989, 14, 251, such as perfluoro(2-n-propoxy)propyl vinyl ether, perfluoro(2-methoxy)propyl vinyl ether, perfluoro(3-methoxy)propyl vinyl ether, perfluoro(2-methoxy)ethyl vinyl ether, le perfluoro(3,6,9-trioxa-5,8-dimethyl)-dodeca-1-ene, perfluoro(5-methyl-3,6-dioxo)-1-nonene. Moreover, perfluoroalkoxyalkyl vinyl ethers monomers carboxylic end-groups or sulfonyl fluoride end-groups, such as perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride, can also be used for the synthesis of the fluorinated elastomers described by this invention. Mixtures of PAVE and PAAVE can also be present in copolymers.
The preferred solvents to carry out the solution polymerisation are advantageously conventional solvents comprising:
The preferred solvents are methyl acetate, acetonitrile and perfluoro-n-hexane in quantities varying from 30 to 60% by weight.
The reaction temperature for the copolymerisation is preferably situated between 20 and 200° C., more preferably between 55 and 140° C. The pressure inside the polymerisation autoclave varies preferably between 2 and 100 bars, and more preferably between 10 and 100 bars, and even more preferably between 20 and 35 bars, according to experimental conditions. Although the interval above are indicative, a person skilled in the art could make appropriate changes as a function by the properties being sought for the elastomers.
According to the process of the invention, the polymerisation can be initiated through the intervention of usual free radical polymerisation initiators. Representative examples of such initiators are azo compounds (such as AIBN), dialkyl peroxydicarbonates, acetylcyclohexanesulfonyl peroxide, dibenzoyl peroxide, alkyl peroxide, alkyl hydroperoxides, dicumyl peroxide, alkyl perbenzoates and alkyl peroxypivalates. Nevertheless, the preference is given to dialkyl peroxydicarbonates, such as diethyl and di-isopropyl peroxydicarbonates and to alkyl peroxypivalates such as t-butyl, t-amyl peroxypivalates and alkyl peroxide, and most particularly still to alkyl peroxypivalates. Preferably, the initial molar ratio between initiator and monomers is between 0.3 and 2%.
For the emulsion polymerisation process, a large range of co-solvents can be envisaged, the solvents being present in a wide range of mixed proportions with water, for example from 30 to 70% by weight. By the same token, anionic, cationic and non-ionic surfactants can be used in quantities varying usually between 1 and 3% by weight. In the emulsion or suspension polymerisation process, water is generally used as a reaction medium. However, the fluorinated monomers are only partially soluble in water, therefore there is a need to use surfactants. In addition, in the emulsion and suspension polymerisation process, a co-solvent can be added to increase the solubility of the fluorinated comonomers. In this case, acetonitrile, acetone or alkyl alkyl ketones such as methyl ethyl ketone, for example, can be employed.
One of the polymerisation processes that can be used is microemulsion as described in EP 0 250 767 or by dispersion, as indicated in U.S. Pat. No. 4,789,717; EP 0 196 904; EP 0 280 312 and EP 0 360 292.
Chain transferring agents can generally be used to regulate and principally reduce the molar masses of the copolymers. Among these, we can cite telogens containing 1 to 10 carbon atoms and terminal bromine or iodine atom such as for example the compounds of type RFX (where RF is a perfluorinated group, RF═CnF2n+1, n=1-10, X designating either a bromine or iodine atoms) or alcohols, ethers, or esters. A diverse list of transfer agents used in telomerization of fluorinated monomers is given in the review “Telomerization reactions of Fluoroalkanes”, B. Améduri and B. Boutevin in the work “Topics in Current Chemistry” (Ed. R. D. Chambers), vol. 192 (1997) p. 165, Springer Verlag 1997.
The elastomers of the present invention can be reticulated using peroxide based systems and triallyl(iso)cyanurate when such copolymers contain iodine and/or bromine atoms at the terminal position of the macromolecule. Peroxide systems are well known as described in EP 0 136 596.
Also, given the presence of sequences of VDF-HFP in the terpolymers, the fluorinated elastomers of this invention, can be reticulated by diamines, bis-amidoximes or polyphenols. These reticulations are described in Rubber World, 1960, 142, 103; U.S. Pat. No. 4,487,878; Prog. Polym. Sc., 1989, 14, 251; U.S. Pat. No. 5,668,221; Angew. Makromol. Chem., 76/77, 1979, 39; Rubber Age, 103, 1971.
The vulcanisation of these elastomers can be achieved by ionic methods as described in U.S. Pat. No. 3,876,654, U.S. Pat. No. 4,259,463, EP 0 335 705 or in review Prog. Polym. Sci., 1989, 14, 251. or in “Fluoroelastomers. A. Van Cleeff. Dans Modern Fluoropolymers. Edited by John Scheirs. John Wiley & Sons, New York, 1997. pp. 597-614.”
The entire range of relative percentages of the diverse copolymers that can be synthesised from the used fluorinated monomers, leading to the formation of fluorinated copolymers and terpolymers, was studied.
The products were analysed by NMR of 1H and 19F. This analysis method allowed the molar percentages of the comomers introduced in the products to be known without ambiguity. For example, we have perfectly established that based on the characterised microstructures given in the literature (Polymer, 1987, 28, 224 and J. Fluorine Chem., 1996, 78, 145) the relationship between characteristic signals of the copolymers HFP/PFSO2F (see Table 1) and terpolymeres HFP/PFSO2F/VDF (table 2) in NMR of 19F and the structure of the products. The chemical displacements of different fluorinated groups are indicated in Tables 1 and 2 below.
The molar percentages of HFP and VDF in the copolymers and the terpolymers were determined using Equations 1 and 2 respectively.
where Li is the value of the integral of the signal situated at −i ppm in the NMR spectrum of 19F.
where Li is the value of the integral of the signal situated at −i ppm in the NMR spectrum of 19F.
The data from Tables 1 and 2 highlights the diades HFP/PFSO2F, VDF/PFSO2F and HFP/VDF as well as the sequences head-to-tail and head-to-head of the VDF units (respectively at −91 and −113, −116 ppm).
The copolymers with these compositions can find uses in the preparation of components of fuel cells such as membranes, O-rings, pump casings, diaphragms possessing excellent resistance to fuels, gasoline, t-butyl methyl ether, alcohol and motor oil, which are combined with good elastomeric properties, and particularly very good resistance at low temperatures. Another advantage of these copolymers is that they can be reticulated in the presence of conventional agents.
Thus the present process comprises several interesting advantages. It should be known:
The following examples are given to illustrate the preferred embodiments of the invention, and should under no circumstances be considered as limiting the scope of the set invention.
A Carius tube in borosilicate of considerable thickness (length, 150 mm; interior diameter, 16 mm; thickness, 2.0 mm; for a total volume of 14 cm3) containing 0.1158 g (0.50 mmol) of t-butyl peroxypivalate at 75%, 2.21 g (4.96 mmol) of perfluoro(4-methyl-3,6-dioaoct-7-ene) sulfonyl fluoride (PFSO2F) and 2.25 g (0.030 mmol) acetonitrile and are connected to a vacuum pump system and purged three times with helium through primary vacuum cycles (100 mm Hg)/helium. Then, after at least five freezing/thawing cycles to eliminate dissolved oxygen is solution, 3.00 g (0.020 mol) of hexafluoropropene (HFP) is trapped in a frozen tube in a liquid nitrogen and acetone bath and the introduced mass in determined by a double weighing. The tube still immersed in the cold bath is sealed and placed in the cavity of a furnace and agitation at 75° C. for 6 hours.
After the copolymerisation, the tube is frozen in liquid nitrogen and then opened. 1.80 g of gas that has not reacted is then trapped. This permits us to deduce the mass conversion rate of HFP according to the following expression:
where mHFP represents the initial mass of HFP that was introduced.
Then, the yellowish liquid obtained is added dropwise into 35 mL of vigorously mixed cold pentane. After being left 1 hour at 0-5° C., the mixture is poured into a separatory funnel and decanted. The clear colorless supernatant is removed while the heavy yellow phase is dried at 70° C. under 1 mmHg for 2 hours. 1.67 g of very viscous and clear liquid is obtained which corresponds to a mass output of 32%. IRTF analysis (IR Nicolet 510 P) of this copolymer reveals the following characteristic vibrations:
IRTF (KBr, cm−1): 1 100-1 300 (νCF); 1 465 (νSO2F).
The composition of the copolymer (that is to say the molar percentages of the two comonomers of the copolymer or the three comonomers of the terpolymer) were determined by NMR of 19F (200 or 250 MHz) at ambiant temperature, acetone or deuterated DMF being the reference solvents. The reference for NMR of 19F is CFCl3. The experimental conditions for the NMR were the following: a flip angle of 30°, a collection time of 0.7 s, a pulse time of 5 s, 128 accumulated scans and a pulse width of 5 μs.
In addition, this NMR analysis of 19F allows us to ensure that the copolymer does not contain any unreacted PFSO2F, which is shown by the absence of a signal at −137.5 ppm, characteristic of one of the ethylene fluoride atoms of the sulfonated monomer.
As an example, the different signals of the NMR spectrum of 19F and their attributes are given in Table 1. We can be sure of the total reactivity of the sulfonated monomer by the absence of the characteristic signals located at −137.5 ppm attributed to one the ethylene fluoride atoms. According to the integrated signals of the NMR corresponding to each comonomer, the respective molar percentages of HFP/PFSO2F in the copolymer are 31.8/68.2 according to Equation 1. The copolymer has the appearance of a colorless resin and a Tg of −48° C. The thermogravimetric analysis (TGA) reveals that the copolymer is stable thermally. To this end, the temperature required for a 5% degradation in air is 155° C. (Table 3).
In a 300 mL Hastelloy reactor (HC 276)™, equipped with an inlet gas valve, a salting-out valve, a pressure indicator, and a rupture disc of HC 276™ and a magnetic mixer turning at 700 rpm, are introduced, (48.5 g (0.11 mol) of PFSO2F); 1.10 g (4.7 mmol) t-butyl peroxypivalate at 75% and 149.8 g of methyl acetate. The reactor is closed and its sealing is verified. The following cycle is conducted three times: the reactor is placed under vacuum, then nitrogen at 10-15 bars is introduced. These cycles allow the degassing of the solution. This is followed by a vacuum of 20 mmHg in the reactor. The reactor is then placed in an acetone/liquid nitrogen bath so as to obtain an interior reactor temperature close to −80° C. The following are introduced successively, 21.0 g HFP (0.14 mol) then 23.0 g vinylidene fluoride (VDF) (0.36 mol) by double weighing of the reactor. The reactor is then placed in an oil bath progressively heated to a temperature of 75° C. and maintained for three hours. The maximum reaction pressure attained is 13 bars. After six hours at the reaction temperature, the pressure observed is 7 bars. After the reaction, the reactor is placed in an ice bath for 30 minutes, degassing then shows a loss of 2.3 g of gas that was not reacted, which corresponds to a conversion rate of gaseous monomers of approximately 95%. The reaction broth is treated as previously by precipitating in cold pentane and drying. The mass of recovered copolymer is 68.2 g. The obtained terpolymer is a viscous orange liquid. The mass output is 74%. The IRTF analysis (IR Nicolet 510 P) of this terpolymer reveal the characteristic vibrations:
IRTF (KBr, cm−1): 1 100-1 300 (νCF); 1 467 (νSO2F).
The characterisation by NMR 19F (Table 2) shows the absence of trace sulfonated monomer and allows us to know the molar percentages if the three comonomers in the terpolymer equal 10% HFP, 71% VDF and 19% of the sulfonated monomer (PFSO2F) according to the Equations 1 and 2. The terpolymer has a Tg of −43° C. The thermogravimetric analysis (TGA) shows that the copolymer is very stable thermally. To this end, the temperature required for a 5% degradation in air is 260° C. (Table 3).
Other copolymerisations of HFP/PFSO2F and terpolymerisations of HFP/VDF/PFSO2F (experimental details and results) are presented in Table 3.
aTemperature of 75° C., for a period of 3 to 6 hours, in the presence of t-butyl peroxypivalate
bAcetonitrile
cMethyl acetate
The advantages related to the present invention are mainly the following:
Although the present invention was described with the aid of specific embodiments, it is understood that many variations and modifications can be attached to these embodiments, and the present application aims to cover such modifications, uses or adaptations of the present invention, generally according to the principals of the invention and including all variations of the present description which will become known or conventional in the field of activity in which the present invention is found, and which can be applied to the essential elements mentioned below, and in accordance with the breadth of the following claims.
Number | Date | Country | Kind |
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2,293,845 | Dec 1999 | CA | national |
2,299,621 | Feb 2000 | CA | national |
Number | Date | Country | |
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Parent | 12878444 | Sep 2010 | US |
Child | 13450074 | US | |
Parent | 11779551 | Jul 2007 | US |
Child | 12878444 | US | |
Parent | 11182858 | Jul 2005 | US |
Child | 11779551 | US | |
Parent | 10168525 | Nov 2002 | US |
Child | 11182858 | US |