EP1129114A1

EP1129114A1 - Method for producing a fast crosslinkable fluororubber

Info

Publication number: EP1129114A1
Application number: EP99947359A
Authority: EP
Inventors: Ralf KRÜGER; David Bryan Harrison
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1998-09-28
Filing date: 1999-09-15
Publication date: 2001-09-05
Also published as: JP2002525401A; WO2000018811A1; AU6083699A; DE19844188A1; CA2345461A1; JP5031943B2

Abstract

The invention relates to a method for producing a fast crosslinkable fluororubber having exclusively hydrogen, alkyl and/or or alkoxy groups in addition to vinylic end groups. The invention also relates to the mixtures of fluororubber obtained therefrom and to their use in the production of all sorts of shaped articles.

Description

Process for producing a rapidly cross-linkable fluororubber

The present invention relates to a process for producing a fluororubber which, in addition to vinyl end groups, is exclusively hydrogen

Has alkyl and / or alkoxy end groups.

According to the prior art, fluoroelastomers are preferably produced by aqueous emulsion or suspension polymerization (UUmann's Encyclopedia of Industrial Chemistry, Vol. A-11, VCH Verlagsgesellschaft, Weinheim 1988, p.

417 ff). In general, inorganic water-soluble peroxides, such as Persulfates, used as initiators and emulsifiers or suspension stabilizers. The addition of chain transfer agents, such as carbon tetrachloride, acetone, diethyl malonate and methanol, is customary for setting the desired molecular weights. In this way, ionic or polar end groups are introduced into the polymer chain, e.g. -COF, -COOH, -COOR or OH groups. These impair fluidity by increasing the viscosity through intermolecular interactions.

There is therefore a need for low-speed, rapidly crosslinkable fluororubbers

Viscosity.

To overcome the problems described, molecular weight regulators which do not result in any ionic, polar or hydrolyzable end groups are used, US Pat. Nos. 5,256,745 and 5,515,863. However, such regulators mostly also act as

Abort if the radical fragment remaining after the transfer is unable to add fluoromonomers and thus start a new chain. To start the chain again, an initiator radical is again required, from which an ionic end group subsequently arises. Initiators that do not provide ionic end groups, such as organic peroxides or azo initiators, are difficult to handle in the preferred aqueous systems because of their insolubility in water.

EP-A-796 877 describes a 2-stage aqueous process, according to which in the

1st stage with a water-soluble initiator a seed latex and in the 2nd step is polymerized with the help of an organic water-insoluble peroxide.

All fluoropolymers produced by known processes contain at least partially ionic end groups which originate from the initiator. When using certain molecular weight regulators such as Diethyl malonate also has the risk that the ester end groups formed saponify during production (including workup) and thus supply an additional proportion of ionic end groups.

EP-A-739 911 describes fluoroelastomers which are “essentially free” of ionic end groups. These fluoroelastomers are produced in an emulsion polymerization in water with the aid of UV radiation. A homogeneous product is not available here because the homogeneous UV Irradiation in large polymerization containers is technically difficult to implement, furthermore the peroxides used are only sparingly soluble in the aqueous medium and there is always the risk of introducing ionic end groups into the polymer through the protic solvent. In addition, the fluoroelastomers described here have no vinyl End group.

Of the non-aqueous processes, polymerizations in the pure liquefied fluoromonomer prove to be unfavorable, since the resulting polymers are usually insoluble in them and swell only slightly. A reproducible polymerization with good heat and mass transfer and thus acceptable space-time yields is just as impossible in this way. In contrast, fluoromonomers can be polymerized well in the presence of certain fluorine-containing solvents, see, for example, US Pat. No. 4,243,770, DE-A-196 40 972.1. US Pat. No. 5,182,342 describes the use of fluorocarbons in the presence of 20% water as the polymerization medium, which meet certain criteria with regard to the F / H ratio and the position of the hydrogens

With all compounds of this type which contain hydrogen and possibly additionally chlorine, there is always the problem that these transfer and / or termination reactions can occur.

In WO 98/15 583 1,1,2-trichlorotrifluoroethane is used as the polymerization medium. However, compounds of this type (chlorofluorocarbons) have considerable ozone depletion potential. For this reason, their technical use is already prohibited in many industrialized countries. The fluororubbers described in this patent contain 0.5 to 2.5 wt% iodine end groups.

In an earlier application DE-197 40 633.5, liquid fluororubbers are produced in inert solvents of the type RF-SO2F or perfluoroalkyl sulfone in the presence of a molecular weight regulator. The fluororubbers described here also have iodine or bromine end groups.

Surprisingly, it has now been found that fluororubbers can be produced which, in addition to vinyl end groups, carry only hydrogen, alkyl and / or alkoxy end groups by polymerizing at least one fluoromonomer by means of organic peroxides as initiators in inert fluorine-containing solvents in the absence of water and molecular weight regulators, where the solvent is chosen so that the monomers are dissolved by it, but the polymers are no longer soluble above 25 to 30 kg / mol.

The present invention therefore relates to a process for the preparation of a fluororubber which, in addition to vinyl end groups, has exclusively hydrogen, alkyl and / or alkoxy end groups, characterized in that at least one fluoromonomer is polymerized using organic peroxides as initiators in at least one inert fluorine-containing solvent in the absence of water and molecular weight regulators, the solvent being chosen so that the monomers are soluble but the polymers having molecular weights above 25 kg / mol are no longer dissolved .

As monomers for the fluororubbers according to the invention, fluorinated, optionally substituted ethylenes, which may contain hydrogen and / or chlorine in addition to fluorine, such as e.g. Vinylidene fluoride, tetrafluoroethylene and chlorotrifluoroethylene, fluorinated 1-alkenes with 2 to 8 carbon atoms, e.g. Hexafluoropropene, 3,3,3-

Trifluoropropene, chloropentafluoropropene, hexafluoroisobutene and / or perfluorinated vinyl ethers of the formula CF ₂ = CF-OX with X = C _r C ₃ -perfluoroalkyl or - (CF ₂ - CFY-O) nR _F , where n = 1-4, Y = F or CF ₃ and R _F = C _r C ₃ perfluoroalkyl, are used.

The combination of vinylidene fluoride, hexafluoropropene and optionally tetrafluoroethylene and / or perfluorinated vinyl ethers, such as e.g. Perfluoro (methy 1-vinyl 1 ether).

The following composition is particularly preferred:

40 to 90 mol% of vinylidene fluoride,

10 to 15 mol% hexafiuoropropylene

0 to 25 mol% tetrafluoroethylene

0 to 25 mol% of perfluorinated vinyl ethers of the formula CF ₂ = CF-OX with X = C _r C ₃ - perfluoroalkyl or - (CF ₂ -CFY-O) nR _F , where n = 1-4, Y = F or CF ₃ and R _F = C _r

C ₃ perfluoroalkyl mean.

In addition, the use of copolymerizable bromine-containing monomers, such as bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1, as described in US Pat. No. 4,035,565, or l-bromo-2,2- difluoroethylene possible for the production of peroxidically crosslinkable fluororubbers. In addition to vinyl end groups, end groups are exclusively hydrogen, alkyl or alkoxy groups, preferably methyl groups in addition to other alkyl groups, depending on the organic peroxide used, for example 2-ethyl-pentyl or isobutyl radicals and the t-butoxy radical.

The number average molecular weights are in the range from 25 to 100 kg / mol, preferably from 40 to 80 kg / mol with molecular weight distributions, defined as M _w / M _n in the range from 1.5 to 3.5. The Mooney viscosities MLι ₊ ι ₀ are at 120 ° C in the range of 1 to 40, preferably 4 to 20. The Mooney viscosity is determined according to DLN 53 523.

The radical polymerization takes place in the presence of at least one peroxide compound as an initiator.

Organic or fluoroorganic dialkylperoxides, diacylperoxides, dialkylperoxydicarbonates, alkylperesters and / or perketals are used as initiators, for example tert-butylperoxipivalate, tert-butylperoxi-2-ethylhexanoate, dicyclohexylperoxidic carbonate, bis (trifluoroacetylperoximide) peroxydimidene peroxydimidene peroxydimidoximide CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) COO} ₂ .

The type and amount to be used depend on the particular reaction temperature. The half-lives of the peroxide to be selected are preferably between 30 and 500 min. Correspondingly, amounts between 0.05 and 1.0 parts by weight of peroxide per 100 parts by weight are preferred. monomers to be converted.

The molecular weights and thus viscosities of the target products are determined exclusively by the amount of initiator and the solubility of the polymer chains in the solvent. The desired molecular weight is set in the first approximation by the ratio of monomer to peroxide conversion. Quantities become accordingly implemented in the range of 1 to 10 mmol peroxide per 100 mol of monomers. The use of regulators is completely dispensed with.

The inert, fluorinated solvent used is characterized in that it does not undergo any significant transfer reactions under the reaction conditions and that the resulting rubber no longer dissolves homogeneously above molecular weights of 25 kg / mol and has no ozone damage potential. As such, certain fluorocarbon or fluorocarbon compounds containing fluorocarbon or heteroatoms are suitable, such as 1,1,1,3,3-pentafluoropropane, 1,1,1,2,3,3-hexafluoropropane, 1,1,2,2 , 3,3-hexafluorocyclopentane, 1,1,2,2-tetrafluorocyclobutane, 1-trifluoromethyl-1, 2,2-trifluorocyclobutane, 2,3-dihydrodecafluoropentane, 2,2-bis (trifluoromethyl) -l, 3- dioxolane, perfiuor (tripropylamine), methoxy-2-hydrohexafluoropropane, methoxynonafluorobutane, perfluorobutanesulfofluoride, perfluorosulfolane or also the compounds of the formula (I) or (II) mentioned in the earlier application DE-197 40 633.5

R _r SO ₂ -R ₂ (I),

in which

R _{j is} a fluorine atom or a perfluoroalkyl radical with 1 -4 C atoms and

R _{2 represents} a perfluoroalkyl radical with 1-4 C atoms and

n = 4 or 5, in particular perfluorobutanesulfofluoride and perfluorosulfolane. 1,1,1,3,3-pentafluoropropane, perfluorobutanesulfofluoride and perfluorosulfolane are preferred individually or in a mixture.

It is advantageous to pay attention to low boiling points of the solvents in order to enable a simple separation between solvent and fluororubber after the polymerization has ended. Due to their low boiling points between 15 and 70 ° C and their low enthalpy of vaporization, the compounds mentioned as preferred can simply be evaporated from the rubber after the polymerization.

The ratio of fluoromonomer (monomer) to solvent and the degree of reactor filling is preferably chosen so that the proportion of the monomer in the liquid phase is at least 20% by weight at the reaction temperature. The amount of monomer dissolved in the liquid phase can e.g. can be determined from the mass balance on the basis of the partial pressures of the monomer in the gas phase.

The reaction temperatures are in the range from -20 to 130 ° C, preferably from 0 to 80 ° C. Lower temperatures lead to an increase in the running time and a sharp increase in the viscosity of the polymer. The space-time yields can no longer be significantly increased with even higher temperatures.

The pressure depends on the aforementioned conditions and on the composition of the monomer mixture and is preferably in the range from 10 to 100 bar, particularly preferably in the range from 15 to 50 bar.

The polymerization can be carried out in a batch, continuous or batch / feed process in stirred tank reactors, the batch / feed process being preferred.

After the polymerization has ended, the reaction mixture can easily be passed through a

Drain or push a riser pipe out of the boiler. The Residual monomers and the solvent can then be easily separated from the polymer by expansion.

The fluoroelastomers according to the invention are excellently suitable for the preparation of fast crosslinkable fluorine rubber mixtures, in particular with ionic Ver ^{"netzersystemen} consisting of a polyhydroxy compound and an onium salt and an acid acceptor.

Examples

example 1

620 ml of perfluorobutanesulfofluoride (PFB _U SF) were placed in a 4.1-1 autoclave. The closed autoclave was evacuated twice with cooling, then pressurized with 3 bar nitrogen pressure and slowly stirred for 10 minutes each. 440 g of vinylidene fluoride (VDF) and 880 g of hexafluoropropene (HFP) were added to the evacuated autoclave and the reaction mixture was heated to 60 ° C. with stirring. After this temperature was reached, the internal pressure in the autoclave was

27 bar. The polymerization was initiated by adding 4.25 g of TBPPI-75-AL (= tert-butyl peroxypivalate as a 75% solution in aliphates, from Peroxid-Chemie GmbH, peroxide content 47.1%) dissolved in 20 g of PFBSF . The polymerisation started after a few minutes. During the polymerization, a monomer mixture of 60% by weight

Vinylidene fluoride and 40 wt .-% hexafluoropropene so that the internal pressure in the autoclave was kept constant at 26.8 + 0.2 bar. In this way, a total of 300 g of vinylidene fluoride and 200 g of hexafluoropropene were replenished within a reaction time of 14 h. After the end of the polymerization, the reaction mixture was cooled and the unreacted monomer mixture was passed through

Expansion and evacuation removed from the reactor. The remaining reactor contents were heated to 80 ° C. with stirring. 15 minutes after the stirrer was switched off, the contents of the reactor were discharged via a bottom drain valve into a second pressure vessel underneath.

After separating the product from PFBSF, it was dried to give 450 g of a rubbery copolymer.

The following copolymer composition was determined by ¹⁹ F-NMR analyzes (solvent: acetone; standard: CFC1 ₃ ): 20.5 mol% of hexafluoropropene,

79.5 mol% vinylidene fluoride. The number average molecular weight (membrane osmosis) was 68,900 g / mol. The MM _n determined by GPC tests was 2.3.

A value of 16 was determined for the Mooney viscosity MLι ₊ ιo at 120 ° C. "

(Table 1).

Example 2

The polymerization was carried out in an analogous manner to that in Example 1, using 1,1,1,3,3-pentafluoropropane instead of PFBSF and 2.5 g of tert-butyl-per-2- instead of TBPPI-75-AL. ethylhexanoate have been used as an initiator, the polymerization temperature has been increased to 78 ° C. and an initial pressure of 33.6 bar has been established accordingly.

After a running time of 15 h, 541 g of rubber were isolated.

Example 3

The polymerization was carried out in a manner analogous to that in Example 1, with 620 ml of 1,1,1,3,3-pentafluoropropane being used as the polymerization medium instead of the PFBSF and the amount of HFP introduced being increased to 1,026 g and an initial pressure correspondingly increasing set from 29 bar.

After a running time of 25 h, 518 g of rubber were isolated (Table 1: Properties).

Comparative Example 1

25.2 kg of deionized water and 30.2 g of lithium perfluorooctyl sulfonate and 29.3 g of oxalic acid dihydrate were placed in a 36-liter autoclave. set a pH of 3 throughout the aqueous receiver. The closed autoclave was evacuated four times, then pressurized with 3 bar nitrogen and each slowly stirred for 10 minutes. 269 g of vinylidene fluoride and 366 g of hexafluoropropene were added to the evacuated autoclave and the reaction mixture was heated to 35 ° C. with stirring. After this temperature had been reached, the internal pressure in the autoclave was 10.5 bar. The polymerization was initiated by adding 53 ml of an aqueous solution containing 20 g / l of potassium permanganate. Immediately after the single addition, said solution became continuous at a rate of 39 ml / h, indicated by the beginning of the decrease in pressure, the polymerization started after 20 min During the polymerization, a monomer mixture of 60% by weight vinylidene fluoride and 40% by weight hexafluoropropene was replenished in such a way that the internal pressure in the autoclave was constant at 10 , 3 + 0.2 bar .. After 250 g of monomer conversion, a total of 80 ml of diethyl malonate was added at a metering rate of 20 ml / h.

A total of 4,641 g of vinylidene fluoride and 3,078 g of hexafluoropropene were metered in in this way within a reaction time of 7.9 h. To terminate the polymerization, the permanganate metering was stopped, the unreacted monomer mixture was removed from the reactor by expansion and evacuation, and the remaining contents of the autoclave were cooled. The resulting latex was precipitated by dropping it into a well-stirred template consisting of 8,000 ml of a 2% CaCl solution, then washed with deionized water and dried in a vacuum drying cabinet at 60 ° C. for 24 h. In this way, 7.5 kg of a rubbery copolymer was isolated.

The following copolymer composition was determined by ¹⁹ F-NMR analyzes: 21.4 mol% hexafluoropropene, 78.6 mol% vinylidene fluoride.

The number average molecular weight was 79,800 g / mol. The M _NV / M _n determined by GPC investigations was 1.97. A value of 34 was determined at 120 ° C. for the Mooney viscosity MLι ₊₁₀ (Table 1).

Table 1

0 by ¹⁹ F NMR 2) by elemental analysis 3) by IR analysis (High Polymers Vol. XXV: Fluoropolymers, ed. L. Wall,

Wiley, New York, 1972, 336) by Η NMR (Balague et al., J. Fluorine Chem. 70, (1995), 215)

At comparable molecular weights (M _n ), the examples according to the invention show lower viscosities than the corresponding product produced by aqueous emulsion polymerization.

Claims

claims

1. A process for the preparation of a fluororubber which, in addition to vinylic end groups, has exclusively hydrogen, alkyl and / or alkoxy end groups, characterized in that at least one fluoromonomer in ^*

The presence of organic peroxides is polymerized in at least one inert fluorine-containing solvent in the absence of water and molecular weight regulators, the solvent being chosen so that the monomers are soluble but the polymers with molecular weights above 25 kg / mol are no longer dissolved.

2. The method according to claim 1, characterized in that the fluoromonomer is vinylidene fluoride or hexafluoropropylene.

3. The method according to claim 1, characterized in that the organic peroxides used are organic or fluoroorganic dialkyl peroxide, diacyl peroxide, dialkyl peroxydicarbonate, alkyl perester and / or perketal.

4. The method according to claim 1, characterized in that 1,1,1,3,3-pentafluoropropane, perfluorobutanesulfofluoride and perfluorosulfolane are used individually or in a mixture as the inert fluorine-containing solvent.

5. The method according to claim 1, characterized in that one polymerizes at a polymerization temperature in the range of 0 to 80 ° C.

Fluororubbers with only vinyl end groups, exclusively hydrogen, alkyl and / or alkoxy end groups made from vinylidene fluoride, hexafluoropropylene and optionally other fluoromonomers with a Mooney viscosity MLI + J _Q measured at 120 ° C in the range from 1 to 40. Fluororubbers according to claim 6, characterized in that the vinyl end groups are -CH = CF ₂ end groups.