CA2299614A1 - Vinylidene fluoride-based fluorinated elastomers with low tg, not containing either tetrafluoroethylene or a siloxane group - Google Patents

Abstract

The present invention describes the synthesis of new fluorinated elastomers having very low glass transition temperatures, good resistance to bases, to petroleum and to fuels and good processing properties. These elastomers contain, for example, from 90 to 50% of vinylidene fluoride (VDF) and from 10 to 50% of perfluoromethyl vinyl ether (PMVE). In this specific case, they are prepared by radical copolymerization of VDF and PMVE in the presence of different organic initiators such as, for example, peroxides, peresters or diazo.

Description

TITLE
Low Tg fluorinated elastomers based on vinylidene fluoride and do not containing neither tetrafluoroethylene, nor siloxane group s FIELD OF THE INVENTION
The present invention describes the synthesis of new fluorinated elastomers with very low glass transition temperatures, good resistance to bases, petroleum and fuels and good processing properties.
These elastomers contain, for example, 90 to 50% fluoride vinylidene (VDF) 1 o and from 10 to 50% of perfluoromethyl vinyl ether (PMVE). In this precise case, they are prepared by radical copolymerization of VDF and PMVE in the presence of different organic initiators such as peroxides, peresters or diazo.
1 s PRIOR ART
Fluorinated elastomers have a unique combination of properties (thermal resistance, to oxidation, to UV, to aging, to agents chemical corrosive and to fuels; low surface tension, constant dielectric and absorption which allowed them to find “high tech” applications in many 2o areas: seals (space, aeronautics), semiconductors (microphone-electronics), hoses, pipes, pump bodies and diaphragms (industries chemical, automobiles and oil).

-2-However, VDF-based elastomers are few. Even if the Kel F ~ (VDF / CTFE) and FLUOREL ~, DAI-EL ~, FKM ~, TECHNOFLON ~ or VITON ~ (A: VDF / HFP; B: VDF / HFP / TFE) have good resistance chemical and thermal, their Tg is not low enough. The weakest value found in the literature is that of VITON ~ B, ie a Tg of -26 ° C. This last value is nevertheless surprising since the manufacturer announces a Tg varying from -5 to -15 ° C for VITON ~ B. Also, to compete with these elastomers, Ausimont proposed a copolymer VDF / HCF = CFCF3 (Technoflon ~), flame resistant and oxidation but having no Tg below -26 ° C and whose comonomer is difficult to access.
The DuPont company has suggested a new generation of elastomers based on of perfluoroalkyl vinyl ether (PAVE) resistant to low temperatures. So, of copolymers have been produced such as TFE / perfluoromethyl vinyl ether (PMVE) (marketed under the name of Kalrez ~ whose Tg does not fall below this from -15 1 s ° C) and TFE / PMVE (EP 0 077 998) Tg = -9 ° C, or TFE /
PAVE (US 4,948,853).
But it is especially the terpolymers which present Tg even more low. Among them, we note: TFE / ethylene / PMVE Tg = -17 ° C or TFE / VDF / PAVE
(Eur. Patent 131.308) and above all: TFE / VDF / PMVE (Viton GLT ~ Tg = -33 ° C).
2 o However, the Tg increases with the percentage of TFE leading to less good processing properties. This was also noticed in EP 0 131 308 who describes the synthesis of TFE / PAVE / VDF, even if elastomers, used as joints

-3-toric, have very good resistance to polar solvents (EP 0 618 241, Ausimont and Japanese patent -A-3066714 Chem. Abstr., 115: 73436 z).
Terpolymerization of TFE with PMVE and F2C = CF [OCF2CF (CF3)) "OC3F ~ (Uschold, Polym. J., 17 (1985) 253) led to elastomers whose Tg (from -9 to -76 ° C) depend on the value of number n of patterns HFPO and the percentage of the two oxygenated comonomers.
This state therefore encouraged us to use VDF, a cheaper and more alkene.
easy to 1 o to implement that the TFE, in larger quantity and to consider the copolymerization original VDF with perfluorovinyl ethers and essentially the PMVE, lower cost monomer than perfluoroalkoxy alkyl vinyl ethers, in order to prepare original elastomers with good resistance to low temperatures and good processability or aid processing properties.
Competitive works closest to the invention A report and two patents describe the copolymerization of VDF but use PAVEs different from PMVE except for one example.
a) NASA report (1966 author: SCHUMAN
2 o The copolymerization of VDF with perfluoroalkyl vinyl ethers FZC = CFORF
(RF = CF3, CZFS and C3F ~) initiated by the AIBN at very high pressures (= 1000 atm) leads to fluorinated elastomers Tg = -20 to -25 ° C (for an elastomer containing 43% of F2C = CFOC2F5) and Tg = -31 ° C (with 31% of FZC = CFOC3F ~ in the copolymer). For a composition of the VDF / PMVE copolymer of approximately 50/50 which requires strong

-4-initial quantities of PMVE (continuous process), very approximate Tg values ranging from -32 to -38 ° C were found.
The disadvantages are: 1 °) the process difficult to implement work and s dangerous (extremely high pressures); 2) both perfluoroalkyl vinyl ethers (RF = C2F5 and C3F ~) more expensive and more difficult to access than the PMVE and 3 °) the use of PMVE in large quantities.
b) US 4,418,186 Emulsion copolymerization of VDF with perfluorovinyl ether 1 o FZC = CFORF where RF represents the group CF2CF (CF3) OC3F ~ has produced elastomers of Tg = -29 to -36 ° C. Introducing a second bridge ether improves flexibility of the copolymer and lowers the value of the Tg. But the disadvantage is the price perfluoroalkyl vinyl ether.
c) EP0077998 15 This patent describes the solution copolymerization (in C1CFZCFC12) of VDF
with perfluorovinyl ether F2C = CF (OCFZCF (CF3)) 20C3F ~ initiated by a perish chlorofluorinated with a Tg of -41 ° C. Again, the price of the comonomer oxygenated risk to be a limitation because its synthesis is particularly complex, as well as the solvent of polymerization (CFC) and the initiator expensive and dangerous to handle.
DETAILED DESCRIPTION OF THE INVENTION
The present invention describes the synthesis of original fluorinated elastomers, vinylidene fluoride (VDF) base and containing a perfluoroalkyl vinyl ether and / or a

-5-perfluoroalkoxyalkyl vinyl ether, and possibly other fluorinated alkenes.
Originality of the present invention resides in the following facts 1 °) The synthesis of fluorinated elastomers based on perfluoroalkyl vinyl ether or perfluoroalkoxy vinyl ether and possibly other fluorinated alkenes, is carried out with the VDF instead of TFE, the latter being widely used commercially for the manufacture of fluorinated elastomers;
2 °) The synthesis of fluorinated elastomers which is discussed in the present invention does does not require the use of monomers carrying siloxane groups, these latter generally contributing to a decrease in Tg;
3) The fluorinated elastomers obtained by the present invention are of composition majority in VDF and minority in perfluoroalkyl vinyl ether or perfluoroalkoxyalkyl vinyl ether;
4) The fluorinated elastomers synthesized by said invention have very low Tg, these elastomers can thus find applications in the field of plastics ("Aid processing" or implementing agents), or other industries of point (aerospace, electronics or automotive, petroleum, transport of fluids very cold such as liquid nitrogen, oxygen and hydrogen). In addition, seals high thermal resistance can be prepared from these elastomers.
2o The present invention relates to the synthesis of fluorinated elastomers based on VDF, as well as their field of applications.
The scope of the present invention extends to all types of processes generally used: emulsion, bulk, suspension polymerization and in

-6-solution. All can be used. Solution polymerization has however been preferentially used.
The various fluorinated alkenes used have at most four atoms of carbon and have the structure R1R2C = CR3R4 where the substituents Rl ~ are such that at least one of them is fluorinated or perfluorinated. This therefore includes: vinyl fluoride (VF), the trifluoroethylene, chlorotrifluoroethylene (CTFE), bromotrifluoroethylene, 1-hydropentafluoropropylene, hexafluoropropene, hexafluoroisobutylene, 3,3,3-trifluoropropene and generally all fluorinated vinyl compounds or perfluorinated.
Furthermore, perfluorovinyl ethers also play the role of comonomers. Among they include the perfluoroalkyl vinyl ethers (PAVE) whose group alkyl has one to 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), 15 described in US 3,291,843 and in the journal Prog. Polym. Sci., Such as the perfluoro (2-n-propoxy) -propylvinyl ether, perfluoro- (2-methoxy) -propyl-vinyl ether; the perfluoro (3-methoxy) propyl vinyl ether, perfluoro- (2-methoxy) -ethylvinyl ether; the perfluoro-(3,6,9-trioxa-5,8-dimethyl) dodeca-1-ene, perfluoro- (5-methyl-3,6-dioxo) -1-nonene.
Mixtures of PAVE and PAAVE may be present in the copolymers.
More particularly, PMVE has been used as a monomer.
The solvents used to carry out the solution polymerization are the following _7_ - The esters of formula R-COO-R 'where R and R' are hydrogen substituents or alkyls may contain from 1 to 5 carbon atoms, but also groups hydroxy OH or ester groups OR "where R" is an alkyl containing from 1 to 5 atoms of carbon. More particularly, R = H or CH3 and R '= CH3, C2H5, iC3H ~, t-C4H9.
- Fluorinated solvents of the type: C1CFZCFC12, C6F14, n-C4Flo, perfluoro-2-butyltetrahydrofuran (FC 75).
- acetone, 1,2-dichloroethane, isopropanol, tert-butanol, acetonitrile or butyronitrile.
lo The preferred solvents are methyl acetate and acetonitrile, in varying amounts.
The reaction temperature range is 20 to 200 ° C. The temperatures preferably used are between 55 and 80 ° C.
In the process according to the invention, the polymerization can be initiated with the intervention of the usual initiators of radical polymerization. Of examples representative of such initiators are the azo, peroxydicarbonates of dialkyl, the acetylcyclohexanesulfonyl peroxide, dibenzoyl peroxide, peroxide of 2 o dicumyle, t-alkyl perbenzoates and t-alkyl peroxypivalates.
We give however, preference is given to dialkyl peroxydicarbonates, such as diethyl and di-isopropyl peroxydicarbonates and t- peroxypivalates alkyl such than t-butyl and t-amyl peroxypivalates and, more particularly again, to t-alkyl peroxypivalates.

_g_ For the emulsion polymerization process, we used a large range of co-solvents, used in various proportions in the mixture with the water. Of even, various surfactants have been used.
One of the polymerization processes used can also be by microemulsion as described in EP 0 250 767 or by dispersion, as indicated in US
4,789,717, EP 0 196 904; EP 0 280 312 and EP 0 360 292.
1 o The reaction pressures vary between 2 and 120 bars depending on the conditions experimental.
Chain transfer agents can generally be used to reduce the molar masses of the copolymers. Among these, we can cite telogen i5 containing bromine or terminal iodine atoms such as, for example, the compounds RFX type (where RF is a perfluorinated group RF = C "F2" + t ~ n = 1 - 10, X
designating a bromine or iodine atom). A list of the various transfer agents used in telomerization of fluorinated monomers is indicated in the review "
Telomerization reactions of Fluoroalkanes ”, B. Améuri and B. Boutevin in the book 'Topics in Carrent 2o Chemistry ”(Ed. RD Chambers), vol. 192 (1997) p. 165, Springer Verlag 1997.
The elastomers of the present invention can be crosslinked using of peroxides when such copolymers contain iodine and / or bromine in terminal position of the macromolecule. Peroxidic systems are good known, such as those described in EP 0 136 596. The vulcanization of these elastomers may be also performed by ionic methods such as those described in US
3,876,654, US
4,259,463, EP 0 335 705 or in the journal Prog. Polym. Sci., 14 (1989) 251.
s The whole range of relative percentages of the various copolymers synthesizable from the fluorinated monomers used, leading to the formation of homopolymers, fluorinated copolymers and terpolymers has been studied.
The products were analyzed by 1 H and 19 F NMR. This method lo analysis allowed to know without ambiguity the percentages of comonomers introduced into products. For example, we have perfectly established the relationships between the characteristic signals of VDF / PMVE copolymers in 19F NMR
(see Table 1) and the structure of the products.

Table 1: NMR characterization of 19F of VDF / PMVE copolymers.
CHEMICAL MOVEMENT STRUCTURE (ppm) -CHZCFZ-CFzCF (OCF3) -CHZCFZ- -52 tBuOCF (OCF3) CFZ- -59 -CHZCFZ-CHZCFZ-CFZCF (OCF3) -CHZCFZ-CHZCFZ- -92; -94 -CHzCFz-CHZCFZ-CFZCHZ- -95 -CFZCF (OCF3) -CHZCFZ-CFZCF (OCF3) - -108 -CHZCFZ-CFZCF (OCF3) -CHZCFZ- -110 tBuOCH2CF2-CHZCFZ- -112 -CF2CF (OCF3) -CFZCF (OCF3) - -117 -CFZCF (OCF3) -CHZCFZ-CFzCF (OCF3) -CHZCFZ- -120 -CHZCFz-CFZCF (OCF3) -CHZCFz- -122 -CHZCFz-CFZCF (OCF3) -CHZCFz- -125 -CHZCFZ-CFZCF (OCF3) -CFzCHz- -126 -CHZCFZ-CF (OCF3) CFZ-CHZCFZ- -136 -CHZCFZ-CF (OCF3) CFZ-CHZCFZ- -144 -CHZCFZ-CF, CF (OCF3) -CFZCHz- -145 The copolymers of such compositions can find applications in preparation of O-rings, pump casings, diaphragms having a very good resistance to fuels, petrol, t-butyl methyl ether, alcohols and oils of motor, combined with good elastomeric properties, in particular a very good resistance to low temperatures. These copolymers also have the advantage of being crosslinkable in the presence of traditionally used agents.
1 o These fluorinated elastomers were characterized by 19F NMR spectroscopy (acetone or deuterated DMF) and the chemical shifts of the different groupings fluorides have been mentioned in Table 1. This analysis highlights the head-tail and head-to-head sequences of VDF unit blocks (respectively -91 and -113, -116 ppm) as well as short blocks of two consecutive PMVE units (for high initial proportions in PMVE).
The following examples are given in order to illustrate implementations s preferential of the invention, and should in no case be considered as limiting the scope of said invention.
Example 1 - VDF / PMVE copolymerization (initial mol% 80/20) A very thick borosilicate Carius tube (length, 130 mm;
lo internal diameter, 10 mm; thickness, 2.5 mm; for a total volume of 8 cm3) containing 0.0242 g (0.104 mmol) 75% t-butyl peroxypivalate and 2.542 g (34.4 mmol) of methyl acetate is connected to a vacuum ramp system and purged three times at helium by primary vacuum cycles (100 mm Hg) / Helium. Then after five cycles at less freezing / thawing (respectively in liquid nitrogen and methanol) to remove the oxygen dissolved in this solution, vinylidene fluoride (VDF) (0P
= 0.35 bar, 0.525 g, 8.20 mmol) then perfluorovinylmethyl ether (PMVE), (OP
= 0.085 bar, 0.3405 g, 2.05 mmol) successively introduced in the gas phase, are trapped under vacuum in the tube frozen in liquid nitrogen, after expansion of the gases located in a reservoir metallic pressure calibrated. The respective quantities of gas (precision ~
8 mg) 2 o introduced into the tube were determined by a relative fall of pressure in this expansion tank, initially filled with a cylinder containing 300 g of VDF or 50 g from PMVE. Beforehand, the two calibration curves "mass of VDF (or PMVE) (in g) as a function of the pressure drop (in bar) ”have been determined. Through example, for 0.750 g of VDF, a pressure difference of 0.50 bar was necessary while to introduce 0.85 g of PMVE a pressure difference of 0.2 bar was enough. The tube, under vacuum and still immersed in liquid nitrogen, is sealed with a torch then place in the cavity of an oven stirred at 75 ° C for 13 hours.
s After copolymerization, the tube is frozen in liquid nitrogen and then connected to the vacuum ramp, tightly closed, and unreacted gases have been trapped in a metal trap previously tared and immersed in liquid nitrogen. 0.044 g gas unreacted was trapped. This allows to deduct the conversion rate mass global gas according to the expression m VDF + mPMVE ~~ 044 - 95 mVDF + mPMVE
where m; represents the masses of gas i initially introduced.
Then, the yellowish liquid obtained is added dropwise to 35 ml of strongly agitated cold pentane. After being left for 1 hour at 0-5 ° C, the mixture is 1 s poured into a separatory funnel.
The clear colorless supernatant is removed while the yellow heavy phase East dried at 70 ° C under 1 mm Hg for 2 hours. 0.80 g of a liquid very viscous, clear has been obtained.
The composition of the copolymer (i.e. the molar percentages of the two comonomers in the copolymer) was determined by NMR of '9F (200 or MHz) at room temperature, acetone or deuterated DMF being the solvents of reference.
For example, the different signals of the 19F NMR spectrum and their s attributions are indicated in Table 1. According to the integrations of the signals corresponding to each comonomer, the respective molar percentages VDF /
PMVE
in the copolymer are 86.6 / 13.4. The resin-like copolymer colorless hard.
Tg = -41.4 ° C (Table 2).
lo Example 2 - VDF / PMVE copolymerization (initial mol% 65/35) Under the same conditions as above, a Carius tube containing 0.525 g (8.20 mmol) of VDF; 0.720 g (4.33 mmol) of PMVE; 0.0312 g (0.13 mmol) of t-butyl peroxypivalate and 2.718 g of methyl acetate is stirred at 75 ° C for 6 hours. After the same treatment and drying, 1.1 g of a very elastomer viscous have been 15 obtained and whose characteristics observed on the NMR spectrum of '9F
indicate a copolymer with a VDF / PMVE molar composition equal to 79.4 / 20.6. Tg = -37.8 ° C
(Table 2).
The following examples corresponding to the synthesis and properties thermal of the copolymers are described in Table 2.
The advantages related to the present invention are mainly the following:
1 °) The synthesis process is carried out in operating mode in cuvée (“batch”);
2) The process in question in the present invention takes place in solution and uses conventional organic solvents, readily available in the trade ;

3 °) The method of said invention consists of a polymerization radical in the presence conventional initiators, readily available commercially;
4) The monomer which mainly enters into the composition of fluorinated elastomers prepared by said invention is VDF; this one is significantly less expensive and much less dangerous than TFE;
5 °) The fluorinated elastomers which are mentioned in said invention can be prepared from the PMVE monomer which is significantly less expensive than the others perfluoroalkyl vinyl ethers and perfluoroalkoxy vinyl ethers, the latter being used in the examples cited above.
lo Although the present invention has been described using implementations specific, it is understood that several variations and modifications may piggyback on said implementations, and the present application aims to cover such modifications, uses or adaptations of the present invention according, in general, to principles of 1 s the invention and including any variation of the present description which will become known or conventional in the field of activity in which this is found invention, and which can be applied to the essential elements mentioned above, in agreement with the scope of the following claims.

Claims (12)

1. Fluorinated elastomers comprising neither tetrafluoroethylene nor of group siloxane and having very low glass transition temperatures (p.
ex. T g = -35 to -42 ° C). 2. Fluorinated elastomers according to claim 1 composed of fluoride vinylidene (VDF) and perfluoromethyl vinyl ether (PMVE). 3. Fluorinated elastomers according to claim 1 or 2 containing from 62 to 87% of VDF and from 32 to 13% of PMVE. 4. Fluorinated elastomers according to claim 1 or 3 prepared in cuvée (“
batch ”). 5. Fluorinated elastomers according to claim 1, 3 or synthesized by radical copolymerization in the presence of commercial organic initiators. 6. Fluorinated elastomers according to claim 1, 3, 4 or 5 prepared in presence of peroxides or peresters. 7. Fluorinated elastomers according to claim 1, 3, 4 or 6 copolymerized mainly in the presence of t-butyl peroxypivalate or t-butyl cyclohehyl peroxydicarbonate. 8. Fluorinated elastomers according to claim 1, 3, 4 or 7 prepared by solution copolymerization in the presence of commercial organic solvents. 9. Fluorinated elastomers according to claim 1, 3, 4, 7 or 8 synthesized in particularly in the presence of perfluoro-n-hexane, acetonitrile or acetate methyl. 10. Fluorinated elastomers according to claim 1, 3, 4, 7 or 9 requiring the perfluoro-n-hexane and / or acetonitrile as solvent. 11. Fluorinated elastomers according to claim 1, 3, 4, 7 or 10 obtained by copolymerization according to the initial molar ratios C0 = [initiator] 0 /
([VDF] 0 +
[PMVE] 0) between 0.3 and 2%. 12. Fluorinated elastomers according to claim 1, 3, 4, 7, 10 or 11 suitable for the manufacture of seals, hoses, pipes, diaphragms (for the automotive, mining, aeronautical, petroleum, electronic industries, watchmaking and nuclear) and for the plastics industry (products to aid in shaping).