Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F214/18—Monomers containing fluorine
  • C08F214/22—Vinylidene fluoride
  • C08F214/222—Vinylidene fluoride with fluorinated vinyl ethers

Definitions

• the present invention relates to the synthesis of new fluorinated elastomers having very low glass transition temperatures (T g ), good resistance to bases, to petroleum and to fuels, as well as good processing properties.
• the elastomers of the invention contain, by way of nonlimiting example, (i) from 50 to 90 mol% of vinylidene fluoride (hereinafter "VDF”) and from 10 to 50 mol% of perfluoromethyl vinyl ether (hereinafter “PMVE”) or (ii) from 55 to 98% by mole of VDF and from 2 to 45% of perfluoropropyl vinyl ether (hereinafter "PPVE”) and possibly other fluorinated alkenes, both in the case of (i) than of (ii).
• VDF vinylidene fluoride
• PMVE perfluoromethyl vinyl ether
• PPVE perfluoropropyl vinyl ether
• the invention also relates to a process for the preparation of these elastomers by radical copolymerization of the comonomers in the presence of various conventional organic initiators, such as peroxides, peresters, diazo or alkyl peroxypivalates.
• organic initiators such as peroxides, peresters, diazo or alkyl peroxypivalates.
• PRIOR ART Fluorinated elastomers exhibit a unique combination of extremely advantageous properties. Among these, mention may be made of their thermal resistance, to oxidation, to ultraviolet (UV) rays, to degradation due to aging, to corrosive chemical agents and to fuels. They also have a low surface tension and a low dielectric constant, and resist absorption of water.
• elastomers based on vinylidene fluoride are few. Even if commercial elastomers such as Kel F ® (VDF / chlorotrifluoroethylene) and Fluorel ® , Dai-El ® , FKM ® , Technoflon ® , Viton ® A or Viton ® B (VDF / HFP / TFE or VDF / HFP) good chemical and thermal resistance, their glass transition temperatures (T g ) are not low enough.
• the T g of the above-mentioned commercial products generally vary between -10 and -20 ° C.
• Viton ® B ie a T g of - 26 ° C, which is surprising since the manufacturer announces a T g varying between -5 and -15 ° C for this product.
• DuPont suggested a new generation of perfluoroalkyl vinyl ether (PAVE) elastomers resistant to low temperatures.
• copolymers have been produced, such as the copolymer of tetrafluoroethylene (TFE) / perfluoromethyl vinyl ether (PMVE) (Kalrez ®), the T g does not fall below -15 ° C, the TFE / PMVE described in EP 0 077 998, the T g of which are -9 ° C, or the TFE / perfluoroalkylvinylether (PAVE) described in US 4,948,853. But it is especially the terpolymers which have even lower T g .
• the terpolymer TFE / ethylene / PMVE whose T g is -17 ° C, or the terpolymer TFE / VDF / PAVE (described in EP 0 131 308), and especially the terpolymer TFE / VDF / PMVE ( Viton GLT ® ) with a T g of -33 ° C.
• the T g increases with the percentage of TFE in the polymer, leading to poorer processing properties.
• EP 0 077 998 describes the copolymerization in solution (in C1CF 2 CFC1 2 ) of VDF with perfluorovinyl ether
• F 2 C CF (OCF 2 CF (CF 3 )) 2 ⁇ C 3 F 7 initiated by a chlorofluorinated perester.
• the T g of the final product is -41 ° C.
• the polymerization solvent used (CFC) and the initiator, which is expensive and dangerous to handle, constitute two significant limitations.
• the synthesis of the oxygenated comonomer is particularly complex.
• the object of the invention is therefore to synthesize new elastomers having a simple manufacturing process which does not require dangerous experimental conditions and which makes it possible to give them a very low glass transition temperature (T g ) from inexpensive comonomers.
• the object of the invention is also to synthesize new elastomers of which the composition of the copolymers, that is to say the molar percentages of each of the comonomers in the copolymer, are known very precisely and without ambiguity.
• the present invention also relates to a process for the synthesis of elastomers comprising a first comonomer, either vinylidene fluoride (VDF), and a second comonomer, either a perfluorinated vinyl ether, in particular a perfluoroalkyl vinyl ether and / or a perfluoroalkoxyalkyl vinyl ether, and possibly other fluorinated alkenes.
• VDF vinylidene fluoride
• the invention relates to a process for the preparation of fluorinated elastomers by copolymerization of vinylidene fluoride with at least one perfluorinated vinyl ether and optionally at least one fluorinated alkene, characterized in that the preparation is carried out by radical copolymerization in the presence of a organic initiator at a temperature between 20 and 200 ° C, for a period of time between 3 and 15 hours, and at an initial pressure between 2 and 100 bars, and said initial pressure is allowed to drop as and when the monomers are consumed.
• the invention also relates to fluorinated elastomers comprising copolymers of vinylidene fluoride, at least one perfluorinated vinyl ether and optionally a fluorinated alkene, characterized in that they contain neither tetrafluoroethylene, nor of monomer carrying siloxane group and have low glass transition temperatures (T g ) between -35 and - 42 ° C.
• the VDF is in the majority in the composition of the elastomer.
• a molar concentration of 50 to 90% of VDF is particularly preferred.
• a perfluoroalkyl vinyl ether such as perfluoromethyl vinyl ether (PMVE) or perfluoropropyl vinyl ether (PPVE) represents a preferred compound.
• the molar concentration of this second comonomer should preferably vary between 10% and 50% in the case of PMVE and from 2 to 45% in the case of PPVE.
• VDF was chosen for the preparation of the elastomers of the present invention, the latter being an alkene which is cheaper and easier to use than TFE. Being less expensive, it can therefore be used in greater quantity in the copolymer, which may comprise as second monomer a perfluorovinyl ether such as PMVE or PPVE, monomers less expensive than perfluoroalkoxy alkyl vinyl ethers, in order to prepare original elastomers having good resistance to low temperatures and good processing properties.
• a perfluorovinyl ether such as PMVE or PPVE
• the present invention therefore relates to the synthesis of original fluorinated elastomeric copolymers, based on vinylidene fluoride (VDF) and containing a perfluorinated vinyl ether, in particular a perfluoroalkyl vinyl ether and / or a perfluoroalkoxyalkyl vinyl ether.
• VDF vinylidene fluoride
• Other fluorinated alkenes can optionally be added.
• a synthesis from VDF instead of conventional tetrafluoroethylene (TFE) the latter being widely used for the manufacture of fluorinated elastomers.
• TFE tetrafluoroethylene
• fluorinated elastomers does not require the use of monomers carrying siloxane groups, the latter generally contributing to a reduction in T g . It is indeed well known that siloxanes have very low T g .
• poly (dimethyl siloxane) have T g of -120 ° C as generally indicated in the following volume: The siloxane bond: physical properties and chemical transformations, MG Voronkov, VP Mileshkevich, and Yu. A. Yuzhelevskii, Consultants Office, New York (1978).
• the fluorinated elastomers of the present invention have very low T g which generally vary from -35 to -45 ° C.
• elastomers can thus find applications in the field of plastics as an implementing agent, or other advanced industries such as aerospace, electronics or the automotive, petroleum, or fluid transport industries. very cold such as liquid nitrogen, liquid oxygen and liquid hydrogen.
• seals of high thermal resistance can be prepared from the elastomers according to the present invention.
• the fluorinated elastomers obtained by the present invention are of majority composition in VDF and minority in perfluoroalkyl vinyl ether or perfluoroalkoxyalkyl vinyl ether, therefore inexpensive.
• the scope of the present invention extends to all types of radical polymerization processes generally used: emulsion, miniemulsion, microemulsion, bulk, suspension, microsuspension and solution polymerization. All can be used according to their conventional implementation, but the solution polymerization was used preferentially for reasons of ease of implementation in the laboratory only, because in the case of solution polymerization, the operating pressures are low, or around 20 to 40 bars. In the case of emulsion, bulk and suspension polymerization, the operating pressure is higher, ie of the order of 40 to 100 bars.
• VF vinyl fluoride
• CFE chlorotrifluoroethylene
• bromotrifluoroethylene 1-hydropentafluoropropylene
• hexafluoropropene hexafluoroisobutylene
• 3,3,3-trifluoropropene 2 - hydropentafluoropropylene
• 1,2-dichlorodifluoroethylene 2-chloro-1,1-difluoroethylene
• perfluorovinyl ethers can also play the role of comonomers.
• PAVE perfluoroalkyl vinyl ethers
• PMVE perfluoromethyl vinyl ether
• PEVE perfluoroethyl vinyl ether
• PPVE perfluoropropyl vinyl ether
• PAAVE perfluoroalkoxy alkyl vinyl ethers
• the preferred solvents for carrying out the solution polymerization are advantageously conventional solvents comprising: - the esters of formula R-COOR 'where R and R' are independently a group C ⁇ . s alkyl, or an ester group OR "where R" is an alkyl containing from 1 to 5 carbon atoms, R may also represent H.
• the usual solvents such as acetone, methyl acetate, 1,2-dichloroethane, isopropanol, tert-butanol, acetonitrile and butyronitrile.
• the preferred solvents are methyl acetate and acetonitrile in variable amounts usually between 30 and 60% by weight.
• the reaction temperature for the copolymerization is preferably between 20 and 200 ° C, more advantageously between 40 and 80 ° C.
• the pressure inside the polymerization vessel preferably varies between 2 and 100 bars, advantageously between 20 and 40 bars, depending on the experimental conditions.
• the polymerization can be initiated by conventional initiators of radical polymerization.
• initiators include azo (such as AIBN), dialkyl peroxydicarbonates, acetylcyclohexanesulfonyl peroxide, dibenzoyl peroxide, alkyl peroxides, alkyl hydroperoxides, dicumyl peroxide, t-alkyl perbenzoates and t-alkyl peroxypivalates.
• alkyl peroxides such as t-butyl peroxide
• dialkyl peroxydicarbonates such as diethyl and di-isopropyl peroxydicarbonates
• t-alkyl peroxypivalates such as t-butyl peroxypivalates. and t-amyl and, more particularly still, to t-alkyl peroxypivalates.
• cosolvents for the emulsion polymerization process, a wide range of cosolvents can be envisaged, the solvents being present in various proportions in the mixture with water, preferably from 30 to 70% by weight.
• anionic, cationic or nonionic surfactants can be used in amounts usually varying from 1 to 3% by weight.
• water is generally used as the reaction medium.
• fluorinated monomers are hardly soluble in water, hence the need to use surfactants.
• a cosolvent can be added to increase the solubility of fluorinated comonomers. In the latter case, acetone or other alkyl alkyl ketones such as methyl ethyl ketone can, for example, be used.
• Chain transfer agents can generally be used to reduce the molecular weights of the copolymers.
• the elastomers of the present invention contain iodine and / or bromine atoms in the terminal position
• these elastomers could be crosslinked (or vulcanized) using peroxides.
• Well-known peroxide systems for example, those described in EP 0 136 596, can perform this task.
• the vulcanization of the elastomers can also be carried out by conventional ionic methods such as those described in US 3,876,654; US 4,259,463; EP 0335 705 or in the journal Prog. Polym. Sel, 1989. 14, 251 or in "Fluoroelastomers. AV Cleeff, in Modem Fluoropolymer. Edited by John Scheirs. John Wiley & Sons, New York, 1997 pp. 597-614.”
• I. j is the value of the integration of the signal located at -i ppm on the NMR spectrum of 19 F.
• copolymers of the present invention can find applications in the preparation of O-rings, pump casings, diaphragms having very good resistance to fuels, petrol, t-butyl methyl ether, alcohols and motor oil, combined with good elastomeric properties, in particular very good resistance to low temperatures.
• the T g of the copolymers obtained is from -35 to -42 ° C (see Table 2). These copolymers also have the advantage of being crosslinkable in the presence of agents conventionally used.
• table 1 highlights the head-tail and head-head sequences of the blocks of VDF units (at -91 and -113, - 116 ppm respectively) as well as short blocks of two consecutive PMVE units (for high initial proportions in PMVE).
• the present process therefore has several interesting advantages, namely: - it is carried out in the cuvée operating mode;
• VDF VDF
• Example 1 VDF / PMVE copolymerization (initial molar percentages 80.0 / 20.0)
• VDF vinylidene fluoride
• PMVE perfluorovinylmethyl ether
• the two calibration curves "mass of VDF (or PMVE) (in g) as a function of the pressure drop (in bar)" were determined. For example, for 0.750 g of VDF, a pressure difference of 0.50 bar was necessary while to introduce 0.850 g of PMVE a pressure difference of 0.20 bar was sufficient.
• the tube, under vacuum and still immersed in liquid nitrogen, is sealed with a torch and then placed in the cavity of an oven stirred at 75 ° C for 13 hours.
• the tube is frozen in liquid nitrogen and then connected to the vacuum manifold, hermetically, open, and the unreacted gases were trapped in a metal trap previously tared and immersed in liquid nitrogen. 0.044 g of unreacted gas was trapped. This allows to deduct the overall mass conversion rate of gases according to the following expression: ⁇ VDF + m PMVE - 0.044
• composition of the copolymer (that is to say the molar percentages of the two comonomers in the copolymer) was determined by NMR of 19 F (200 or 250 MHz) at room temperature, acetone or DMF deuterated being the solvents reference.
• the ! 9 F NMR reference is CFC1 3 .
• the NMR experimental conditions were as follows: 30 ° of the "flip" angle, 0.7 s of acquisition time, 5 s of "dip” time, 128 "accumulation scans" and 5 ⁇ s width of "draws”.
• the various signals of the 19 F NMR spectrum and their assignments are indicated in Table 1 above.
• the respective molar percentages VDF / PMVE in the copolymer are 86.6 / 13.4.
• the copolymer has the appearance of a colorless resin.
• the measured T g is -41.4 ° C.
• VDF / PMVE copolymerization (initial molar percentages 65.4 / 34.6)
• Table 2 groups together the information corresponding to the synthesis and to the thermal properties of the VDF / PMVE copolymers .
• C 0 [initiator] 0 / ([VDF] 0 + [PMVE] 0 ).
• the value of C 0 generally varies from 0.1 to 2%.
• VDF is more reactive than PMVE, that is to say that VDF is better incorporated into the copolymer.
• the molar percentage of VDF in the copolymer is greater than the initial molar percentage of VDF introduced into the reactor. In each case of polymerization, the yield is above 80%.
• the radical copolymerizations in solution are carried out in a thick Carius tube as described in Examples 1 and 2 above.
• the initiator used is tert-butyl peroxide, (CH 3 ) 3 C-0-0-C (CH 3 ) 3 .
• the solvent used is acetonitrile known to be a good solvent for the monomers, and not transferable.
• the copolymerization is carried out at 120 ° C for 16 hours.
• Several experiments are carried out according to different initial molar percentages of VDF and PPVE as indicated in Table 3.
• the VDF / PPVE copolymer obtained in the reaction crude, is precipitated in cold pentane (0 -5 ° C) strongly agitated.
• the copolymers are in the form of viscous oils. They are then characterized by 19 F NMR. Table 3 groups the results in question and indicates the glass transition temperatures (T g ) measured.
• microstructures of these copolymers were perfectly characterized from the signals of the different groups assigned to the VDF and PPVE units, i.e. the same chemical shifts as those presented in Table 1 with the differences that there is absence of signals at -52 ppm but presence of the following signals: -81 ppm for CF 3 CF 2 CF 2 0-; -129 ppm for CF 3 CF 2 CF 2 0-; -78 ppm for CF 3 CF 2 CF 2 0-.
• VDF V 1-91 + l-92 ⁇ * " l-9 4 1-95 + 1-108 + 1-110 + 1-112 + 1-113 + 1-116

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