Note: Descriptions are shown in the official language in which they were submitted.
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
A method of nroducin~ a rapid-crosslinkin~ fluorinated rubber
The present invention relates to a method of producing a fluorinated rubber,
which
apart from vinyl terminal groups exclusively comprises hydrogen, alkyl and/or
alkoxy
terminal groups.
According to the prior art, fluoroelastomers are preferably produced by
aqueous
emulsion or suspension polymerisation (I111mann's Encyclopedia of Industrial
Chemistry', Vol. A-11. VCH Verlagsgesellschaft, Weinheim 1988, pages 417 et
seq.).
Inorganic. water-soluble peroxides, such as persulphates for example, are
generally
used as initiators and as emulsifiers or suspension stabilisers in processes
such as
these. In order to obtain the desired molecular weight. the addition of chain
transfer
agents such as tetrachloromethane. acetone, diethyl malonate and methanol is
customary. In this manner, ionic or polar terminal groups are introduced into
the
polymer chain. such as -COI~, -COOH, -COOR or OH groups for example. These
impair flowability by increasing the viscosity due to intermolecular
interactions.
There is therefore a need for rapid-crosslinking fluorinated rubbers which
have a low
mscositv.
~0
In order to overcome the problems described above, molecular weight regulators
are
used which do not give rise to any ionic, polar or hydrolysable terminal
groups; see
US-P-5 256 745 and US-P 516 863. For the most part. however, regulators such
as
these also act as terminators if the radical fragment which remains after
transfer is not
2~ capable of adding fluoromonomers and thus of starting a new chain. Thus in
order to
start a new chain an initiator radical is again necessary, from which an ionic
terminal
group is consequently formed again, however.
Initiators which do not give rise to ionic terminal groups, such organic
peroxides or
>0 azo initiators for example, are difficult to handle in the preferred
aqueous systems due
to their insolubility in water.
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-7_
EP-A-796 877 describes a 2-stage aqueous method in which a seed latex is
produced
in the 1 st stage by means of a water-soluble initiator and is further
polymerised in the
2nd stage by means of an organic peroxide which is insoluble in water.
All fluoropolymers produced by known methods contain terminal groups which are
ionic at least in part and which originate from the initiator. Moreover, when
certain
molecular weight regulators are used, such as diethyl malonate for example,
there is a
risk of the ester terminal groups undergoing saponification during production
(including work-up) and thus of furnishing an additional proportion of ionic
terminal
groups.
EP-A-739 911 describes fluoroelastomers which are "substantially free'" from
ionic
terminal groups. These fluoroelastomers are produced in an emulsion
polymerisation
process in water by means of UV irradiation. A homogeneous product cannot be
1 ~ obtained here. because homogeneous UV irradiation is difficult to
accomplish
industrially in large polymerisation vessels. Moreover, the peroxides used are
only
soluble with difficulty in the aqueous medium and there is always the risk of
ionic
terminal groups being introduced into the polymer by the protic solvent. In
addition,
the tluoroelastomers described there do not contain a vinyl terminal group.
~0
Of the nonaqueous methods, polymerisation processes conducted in the pure
liquefied
fluoromonomer have proved to be disadvantageous, since the polymers formed are
mostly insoluble therein and also only swell to a slight extent. Moreover, it
is not
possible by this route to conduct polymerisation reproducibly with good heat-
and
2 ~ mass transfer and therefore with acceptable space-time yields.
In contrast, fluoromonomers can be polymerised well in the presence of certain
tluorine-containing solvents: see US-4 243 770 and DE-A-196 40 972.1, for
example.
US-~ 182 342 describes the use of fluorohydrocarbons in the presence of up to
20
_s0 water as polymerisation media which fulfil certain criteria with regard to
the F/H ratio
and with regard to the position of hydrogen. With all compounds of this type,
which
contain hydrogen and which possibly also contain chlorine in addition, there
is always
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-3-
the problem that they are capable of taking part in transfer and/or
termination
reactions.
In WO 98/15 X83, 1,1,2-trichlorotrifluoroethane is used as a polymerisation
medium.
S However. compounds of this type (chlorofluorocarbons) exhibit a significant
ozone-
damaging potential. For this reason, the industrial use thereof is already
prohibited in
many industrialised countries. The fluorinated rubbers described in the above
patent
contain 0.5 to 2.5 % by weight of iodine terminal groups.
In a previous Application, namely DE-197 40 633.5, liquid fluorinated rubbers
are
produced in inert solvents of the RF-SO~F or perfluoroalkylsulphone type in
the
presence of a molecular weight regulator. The fluorinated rubbers described
there
likewise comprise iodine or bromine terminal groups.
Surprisingly, it has now been found that fluorinated rubbers which apart from
vinyl
terminal groups exclusively comprise hydrogen, alkyl and/or alkoxy terminal
groups
can be produced by the polymerisation of least one fluoromonomer by means of
organic peroxides as initiators in inert fluorine-containing solvents and in
the absence
of water and molecular weight regulators, wherein the solvent is selected so
that the
monomers are soluble therein but polymers with molecular weights higher than
25 to
kg/mol are no longer soluble.
The present invention therefore relates to a method of producing a fluorinated
rubber
which apart from vinyl terminal groups exclusively comprises hydrogen, alkyl
and/or
25 alkoxy terminal groups, characterised in that at least one fluoromonomer is
polymerised by means of organic peroxides as initiators in at least one inert
fluorine-
containing solvent in the absence of water and molecular weight regulators,
wherein
the solvent is selected so that the monomers are soluble but polymers with
molecular
weights higher than 25 kg/mol are no longer dissolved.
_~ 0
The monomers which can be used for the fluorinated rubbers according to the
invention comprise fluorinated ethylenes, which are optionally substituted,
and which
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-4-
apart from fluorine may contain hydrogen and/or chlorine, such as vinylidene
fluoride.
tetrafluoroethylene and chlorotrifluoroethylene for example, fluorinated I -
alkenes
containing 2 to 8 carbon atoms, such as hexafluoropropene, 3,3,3-
trifluoropropene.
chloropentafluoropropene and hexafluoroisobutene for example, and/or
perfluorinated
vinyl ethers of formula CFZ=CF-O-X where X = a Ci-C3 perfluoroalkyl or -(CF=-
CFY-O)°-RF, wherein n = I-4, Y = F or CF3 and RF = a C~-C3
perfluoroalkyl.
A combination of vinylidene fluoride and hexafluoropropene and optionally of
tetrafluoroethvlene and/or of perfluorinated vinyl ethers. such as
perfluoro(methvl-
I 0 vinyl ether) for example, is preferred.
The following composition is particularly preferred:
40 to 90 11101 °'° vinylidene fluoride
to 15 mol % hexafluoropropylene
1 ~ 0 to 25 mol % tetrafluoroethylene
0 to 25 mol % of perfluorinated vinyl ethers of formula CFZ=CF-O-X, where X =
a
Ci-C, pertluoroalkyl, or -(CFA-CFY-O)"-RE:, wherein n = I-4. Y = F or CF, and
RF =
a C,-C; perfluoroalkyl.
~'0 In addition, it is also possible to use copolymerisable monomers which
contain
bromine, such as bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1
as
described in US-A-4 035 565, or I-bromo-2,2-difluoroethylene for the
production of
fluorinated rubbers which can be crosslinked by peroxides.
~5 Apart from vinyl terminal groups, the terminal groups are exclusively
hydrogen, alkyl
or alkoxy groups, and are preferably methyl groups in addition to other alkyl
groups
depending on the organic peroxide used, e.g. 2-ethyl-pentyl or isobutyl
radicals as
well as the t-butoxy radical.
s0 The number average molecular weights fall within the range from 25 to 100
kg/mol,
preferably from 40 to 80 kg/mol, with molecular weight distributions, defined
as
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-5-
M~,,/M", within the range from 1.5 to 3.5. The Mooney viscosities ML,+io at
120°C
fall within the range from 1 to 40, preferably from 4 to 20. The Mooney
viscosity is
determined according to DIN 53 523.
Radical polymerisation is effected in the presence of at least one peroxide
compound
as an initiator.
Organic or fluorinated organic dialkyl peroxides. diacyl peroxides, dialkyl
peroxydicarbonates, alkyl peresters and/or perketals are used as initiators,
e.g. tert-
butyl peroxypivalate. tert-butyl peroxy-2-ethyl-hexanoate, dicyclohexyl peroxy-
dicarbonate, bis(trifluoroacetyl peroxide) or the peroxide of the
hexafluoropropene
oxide dimer ;CF,CF.,CFZOCF(CF3)COO},.
The type and amount of initiator used depend on the reaction temperature
concerned.
I ~ The peroxides which are selected preferably have half-lives between 30 and
500
minutes. Accordingly, amounts between 0.05 and 1.0 parts by weight of peroxide
per
100 parts by weight of monomers to be converted are preferably required.
The molecular weights and thus the viscosities of the target products are
exclusively
?0 determined by the amount of initiator and by the solubility of the polymer
chains in
the solvent. To a first approximation, the desired molecular weight is set by
the ratio
of monomer conversion to peroxide conversion. Amounts within the range from 1
to
10 mmol peroxide per 100 mol monomer are accordingly reacted. The use of
regulators is completely dispensed with.
~' S
The inert fluorinated solvent which is used is characterised in that it enters
into no
significant transfer reactions under the reaction conditions, no longer
homogeneously
dissolves the resulting rubber above a molecular weight of 25 kg/mol, and
exhibits no
ozone-damaging potential. Certain fluorocarbon compounds or fluorohydrocarbon
_~ 0 compounds which contain fluorohydrocarbons or hetero atoms are suitable
as inert
fluorine-containing solvents, such as 1,1,1,3,3-pentafluoropropane,
1,1,1,2,3,3-
hexafluoro-propane, 1,1,2,2,3,3-hexafluorocyclopentane, 1,1,2,2-
tetrafluorocyclo-
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-6-
butane, 1-trifluoromethyl-1,2,2-trifluorocyclobutane, 2,3-dihydrodecafluoro-
pentane,
2,2-bis(trifluoromethyl)-1,3-dioxolane, perfluoro(tripropylamine), methoxy-2-
hydro-
hexafluoropropane, methoxynonafluorobutane, perfluorobutane sulphofluoride or
perfluorosulpholane, and also the compounds of formulae (I) or (II)
R~-SOZ-Rz (I)
( 11).
(CF~)~
which are cited in the prior Application DE-197 40 633.5.
wherein
Ri represents a fluorine atom or a perfluoroalkyl radical comprising 1-4 C
atoms,
1 ~ R, represents a perfluoroalkyl radical comprising 1-4 C atoms, and
n = 4 or ~. particularly perfluorobutane sulphofluoride and
perfluorosulpholane.
1,1.1,3.3-pentafluoropropane, perfluorobutane sulphofluoride and perfluoro-
~0 sulpholane, individually or in admixture, are preferred.
It is advantageous to ensure that the solvents have low boiling points, in
order to
facilitate ease of separation of the solvent from the fluorinated rubber after
the
completion of polymerisation. On account of their low boiling points between
15 and
~ 70°C and their low enthalpies of evaporation, the compounds cited as
preferred can
readily be separated by volatilisation from the rubber after polymerisation.
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
The ratio of fluoromonomer (monomer) to solvent, as well as the reactor
filling ratio,
are preferably selected so that at the temperature of reaction the content of
monomer
in the liquid phase is at least 20 % by weight. The amount of monomer
dissolved in
the liquid phase can be determined from the mass balance by means of the
partial
~ pressure of the monomer present in the gas phase, for example.
The temperatures of reaction fall within the range from -~?0 to 130°C,
preferably from
0 to 80°C. Lower temperatures result in a prolongation of the time of
reaction and in a
considerable increase in the viscosity of the polymer. Moreover, it is not
possible to
I 0 achieve a significant increase in space-time yields by employing higher
temperatures.
The pressure depends on the aforementioned conditions and on the composition
of the
monomer mixture; it preferably falls within the range from 10 to 100 bar, and
is most
preferably within the range from 15 to 50 bar.
1~
Polymerisation can be effected by a batch, continuous or batch-feed process in
stirred
tank reactors. wherein a batch-feed process is preferred.
After the completion of polymerisation, the reaction mixture can readily be
discharged
~0 from or pushed out of the vessel via a bottom outlet or an ascending pipe.
The residual
monomers and solvent can then readily be separated from the polymer by
depressurisation.
The fluorinated rubbers according to the invention ~~re mainly suitable for
the
~5 production of rapid-crosslinking fluorinated rubber compounds, particularly
by means
of ionic crosslinking agent systems consisting of a polyhydroxy compound, an
onium
salt and an acid acceptor.
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-g_
Examples
Example 1
~ 620 ml perfluorobutane sulphofluoride (PFB°SF) were placed in a 4.1
litre autoclave.
The closed autoclave was evacuated twice whilst being cooled, was subsequently
subjected to a nitrogen pressure of 3 bar and was slowly stirred for 10
minutes each
time. 440 g vinylidene fluoride (VDF) and 880 g hexafluoropropene (HFP) were
added to the evacuated autoclave and the reaction mixture was heated to
60°C with
I 0 stirring . After this temperature had been reached, the autoclave internal
pressure was
27 bar. Polymerisation was initiated by the addition of 4.25 g TBPPI-75-AL
(=tert.-
butvl peroxypivalate as a 75 °,'° solution in aliphatic
compounds, supplied by Peroxid-
Chemie GmbH. peroxide content 47.1 %) dissolved in 20 g PFBSF. Polymerisation
commenced within a few minutes, as could be identified by the pressure
starting to
I ~ decrease. During the polymerisation, a monomer mixture comprising 60 % by
weight
vinylidene fluoride and 40 % by weight hexafluoropropene was fed in under
pressure
so that the autoclave internal pressure was held constant at 26.8 ~ 0.2 bar.
In this
manner, a total of 300 g vinylidene fluoride and 200 g hexafluoropropene were
subsequently added over a time of reaction of 14 hours. After the completion
of
~0 polymerisation the reaction mixture was cooled and the unreacted monomer
mixture
was removed from the reactor by depressurisation and evacuation. The remaining
reactor contents were heated to 80°C with stirring. 15 minutes after
switching off the
stirrer, the reactor contents were discharged via a bottom outlet valve into a
second
pressure vessel situated underneath.
~' S
The product was separated from the PFBSF and dried, whereupon 450 g of a
rubber-
like copolymer were obtained.
The following copolymer composition was determined bv'9F NMR analyses
(solvent:
30 acetone; standard: CFC13): 20.5 mol % hexafluoropropene, 79.5 mol %
vinylidene
fluoride.
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-9-
The number average molecular weight (membrane osmosis) was 68,900 g/mol.
M,v/M" was 2.3 as determined by GPC investigations.
A value of 16 was determined for the Mooney viscosity MLi+io at 120°C
(Table 1).
J
Example 2
Polymerisation was conducted analogously to Example l, except that 1,1,1,3,3-
pentafluoropropane was used instead of PFBSF and 2.5 g tert.-butyl per-2-
I 0 ethylhexanoate was used as the initiator instead of TBPPI-75-AL, the
temperature of
polymerisation was increased to 78°C and the initial pressure was
accordingly 33.6
bar.
After a run time of 1 ~ hours, 541 g rubber were isolated.
IS
Example 3
Polymerisation was conducted analogously to Example l, except that 620 ml
1.1,1.3,3-pentafluoropropane was used as the polymerisation medium instead of
?0 PFBSF and the initial amount of HFP was increased to 1026 g. The initial
pressure
was accordingly 29 bar.
After a run time of 25 hours. 518 g rubber were isolated (Table 1:
Properties).
?5 Comparative Example 1
25.2 kg deionised water, 30.2 g lithium perfluorooctyl sulphonate and 29.3 g
oxalic
acid dihydrate were placed in a 36 litre autoclave, which resulted in a pH of
3 in the
aqueous starting mixture as a whole. The closed autoclave was evacuated four
times,
30 followed in each case by subjecting it to a nitrogen pressure of 3 bar and
slowly
stirring the contents for 10 minutes. 269 g vinylidene fluoride and 366 g
hexafluoropropene were added to the evacuated autoclave and the reaction
mixture
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
-10-
was heated to 35°C with stirring. After this temperature had been
reached, the
autoclave internal pressure was 10.5 bar. Polymerisation was initiated by the
addition
of 53 ml of an aqueous solution which contained 20 g/1 potassium permanganate.
Immediately after this first addition, said solution was continuously metered
in at a
rate of 39 ml/hour. Polymerisation commenced after 20 minutes, as could be
identified by the pressure starting to decrease. During the polymerisation, a
monomer
mixture comprising 60 % by weight vinylidene fluoride and 40 % by weight
hexatluoropropene was fed in under pressure so that the autoclave internal
pressure
was held constant at 10.3 ~ 0.2 bar. After 250 g monomer had been converted, a
total
of 80 ml diethyl malonate were metered in at a rate of 20 ml/hour.
' In this manner. a total of 4641 g vinylidene fluoride and 3078 g
hexafluoropropene
were added over a time of reaction of 7.9 hours. In order to terminate the
polymerisation. the addition of permanganate was stopped, the unreacted
monomer
1 ~ mixture was removed from the reactor by depressurisation and evacuation
and the
remaining autoclave contents were cooled. The resulting latex was precipitated
by
adding it drop-wise to a well stirred receiver liquid consisting of 8000 ml of
a 2
solution of CaCI~, and was subsequently washed with deionised water and dried
for
24 hours at 60°C in a vacuum drying oven. 7.5 kg of a rubber-like
copolymer were
~0 isolated in this manner.
The following copolymer composition was determined by '9F NMR analyses: 21.4
mol % hexafluoropropene, 78.6 mol % vinylidene fluoride.
2 ~ The number average molecular weight was 79,800 g/mol. M,~/M" was 1.97 as
determined by GPC investigations.
A value of 34 was determined for the Mooney viscosity IVILi+io at 120°C
(Table 1).
CA 02345461 2001-03-23
WO 00/18811 PCT/EP99/06836
Table 1
Example Example Example Comparative
1 2 3
Example
1
ML, _, at 120C 16 4 17 34
M (kg mol- ) 69 43 57 80
M~~/M" 2.3 2.0 2.8 2.0
VDF content (mol 79.5 79.1 79.5 78.6
%)
Cl. Br or I terminalno no no no
groups-
Carbonyl terminal no no no yes
' ;
groups
Hydroxyl terminal no no no no
groups
-CH=CFZ terminal yes yes yes no
groups3
H. alkyl and alkoxyyes yes yes no
terminal '~roups~
by ' ''F NMR
'~ by elemental analysis
by IR analysis (High Polymers Vol. XXV: Fluoropolymers, ed. L. Wall,
Wiley. New York. 1972, 336)
by ' H NMR (Balague et al., J. Fluorine Chem. 70, (1995), 215)
At comparable molecular weights (M°), the examples according to the
invention have
lower viscosities than the corresponding product produced by aqueous emulsion
polymerisation.
