U.S. patent application number 11/457500 was filed with the patent office on 2007-01-18 for aqueous emulsion polymerization of fluorinated monomers using a perfluoropolyether surfactant.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to KLAUS HINTZER, Michael Jurgens, Harald Kaspar, Kai Helmut Lochhaas, Andreas R. Maurer, Tilman Zipplies.
Application Number | 20070015865 11/457500 |
Document ID | / |
Family ID | 34897174 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070015865 |
Kind Code |
A1 |
HINTZER; KLAUS ; et
al. |
January 18, 2007 |
AQUEOUS EMULSION POLYMERIZATION OF FLUORINATED MONOMERS USING A
PERFLUOROPOLYETHER SURFACTANT
Abstract
The invention relates to an aqueous emulsion polymerization of
fluorinated monomers using perfluoropolyethers of the following
formula (I) or (II). In particular, the perfluoropolyether
surfactants correspond to formula (I) or (II)
CF.sub.3--(OCF.sub.2).sub.m--O--CF.sub.2--X (I) wherein m has a
value of 1 to 6 and X represents a carboxylic acid group or salt
thereof,
CF.sub.3--O--(CF.sub.2).sub.3--(OCF(CF.sub.3)--CF.sub.2).sub.z--O-L-Y
(II) wherein z has a value of 0, 1, 2 or 3, L represents a divalent
linking group selected from --CF(CF.sub.3)--, --CF.sub.2-- and
--CF.sub.2CF.sub.2-- and Y represents a carboxylic acid group or
salt thereof. The invention further relates to an aqueous
dispersion of a fluoropolymer having the aforementioned
perfluoropolyether surfactant(s).
Inventors: |
HINTZER; KLAUS; (Kastl,
DE) ; Jurgens; Michael; (Neuoetting, DE) ;
Kaspar; Harald; (Burgkirchen, DE) ; Lochhaas; Kai
Helmut; (Neuoetting, DE) ; Maurer; Andreas R.;
(Langenneufnach, DE) ; Zipplies; Tilman;
(Burghausen, DE) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
34897174 |
Appl. No.: |
11/457500 |
Filed: |
July 14, 2006 |
Current U.S.
Class: |
524/544 |
Current CPC
Class: |
C08F 14/18 20130101;
C08F 14/18 20130101; C08F 14/18 20130101; C08F 2/22 20130101; C08F
2/24 20130101 |
Class at
Publication: |
524/544 |
International
Class: |
D06M 15/277 20060101
D06M015/277 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2005 |
GB |
GB0514387.0 |
Claims
1. Method for making a fluoropolymer comprising an aqueous emulsion
polymerization of one or more fluorinated monomers wherein said
aqueous emulsion polymerization is carried out in the presence of a
perfluoropolyether as an emulsifier, said perfluoropolyether being
selected from the group consisting of perfluoropolyethers according
to formula (I): CF.sub.3--(OCF.sub.2).sub.m--O--CF.sub.2--X (I)
wherein m has a value of 1 to 6 and X represents a carboxylic acid
group or salt thereof, perfluoropolyethers according to formula
(II):
CF.sub.3--O--(CF.sub.2).sub.3--(OCF(CF.sub.3)--CF.sub.2).sub.z--O-L-Y
(II) wherein z has a value of 0, 1, 2 or 3, L represents a divalent
linking group selected from --CF(CF.sub.3)--, --CF.sub.2-- and
--CF.sub.2CF.sub.2-- and Y represents a carboxylic acid group or
salt thereof, and mixtures of perfluoropolyethers according to
formula (I), (II), or combination thereof.
2. Method according to claim 1 wherein said one or more fluorinated
monomers comprise one or more gaseous fluorinated monomers.
3. Method according to claim 1 wherein said one or more fluorinated
monomers comprise perfluorinated monomers.
4. Method according to claim 1 wherein said aqueous emulsion
polymerization is carried out in the presence of a fluorinated
liquid and wherein said fluorinated liquid is emulsified using said
perfluoropolyether as an emulsifier.
5. Method according to claim 1 wherein said aqueous emulsion
polymerization is carried out using said perfluoropolyether as the
only emulsifier.
6. Method according to claim 1 wherein the amount of said
perfluoropolyether is between 0.01 and 5% by weight based on the
amount of water in the emulsion polymerization.
7. A dispersion comprising an aqueous dispersion of a fluoropolymer
and a perfluoropolyether as an emulsifier, said perfluoropolyether
being selected from the group consisting of perfluoropolyethers
according to formula (I):
CF.sub.3--(OCF.sub.2).sub.m--O--CF.sub.2--X (I) wherein m has a
value of 1 to 6 and X represents a carboxylic acid group or salt
thereof, perfluoropolyethers according to formula (II):
CF.sub.3--O--(CF.sub.2).sub.3--(OCF(CF.sub.3)--CF.sub.2).sub.z--O-L-Y
(II) wherein z has a value of 0, 1, 2 or 3, L represents a divalent
linking group selected from --CF(CF.sub.3)--, --CF.sub.2-- and
--CF.sub.2CF.sub.2-- and Y represents a carboxylic acid group or
salt thereof, and mixtures of perfluoropolyethers according to
formula (I), (II), or combination thereof.
8. A dispersion according to claim 7 wherein said dispersion is
free of perfluoroalkanoic acids or salts thereof.
9. A dispersion according to claim 7 wherein the amount of said
perfluoropolyether is between 0.001 and 5% by weight based on the
fluoropolymer solids.
10. A dispersion according to claim 7 wherein the amount of
fluoropolymer solids is between 10 and 30% by weight.
11. A dispersion according to claim 7 wherein the amount of solids
is more than 30 and up to 70% by weight.
12. A dispersion according to claim 7 wherein the dispersion
further comprises a non-ionic surfactant.
13. A method comprising coating or impregnating a substrate using
an aqueous dispersion as defined in claim 7.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Great Britain Patent
Application No. GBO514387.0, filed on Jul. 15, 2005, herein
incorporated by reference in its entirety.
[0002] The present invention relates to the aqueous emulsion
polymerization of fluorinated monomers to produce
fluoropolymers.
BACKGROUND OF THE INVENTION
[0003] Fluoropolymers, i.e. polymers having a fluorinated backbone,
have been long known and have been used in a variety of
applications because of several desirable properties such as heat
resistance, chemical resistance, weatherability, UV-stability etc.
The various fluoropolymers are for example described in "Modern
Fluoropolymers", edited by John Scheirs, Wiley Science 1997.
Commonly known or commercially employed fluoropolymers include
polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene
(TFE) and hexafluoropropylene (HFP) (FEP polymers), perfluoroalkoxy
copolymers (PFA), ethylene-tetrafluoroethylene (ETFE) copolymers,
terpolymers of tetrafluoroethylene, hexafluoropropylene and
vinylidene fluoride (THV) and polyvinylidene fluoride polymers
(PVDF). Commercially employed fluoropolymers also include
fluoroelastomers and thermoplastic fluoropolymers.
[0004] Several methods are known to produce fluoropolymers. Such
methods include suspension polymerization as disclosed in e.g. U.S.
Pat. No. 3,855,191, U.S. Pat. No. 4,439,385 and EP 649863; aqueous:
emulsion polymerization as disclosed in e.g. U.S. Pat. No.
3,635,926 and U.S. Pat. No. 4,262,101; solution polymerization as
disclosed in U.S. Pat. No. 3,642,742, U.S. Pat. No. 4,588,796 and
U.S. Pat. No. 5,663,255; polymerization using supercritical
CO.sub.2 as disclosed in JP 46011031 and EP 964009 and
polymerization in the gas phase as disclosed in U.S. Pat. No.
4,861,845.
[0005] Currently, the most commonly employed polymerization methods
include suspension polymerization and especially aqueous emulsion
polymerization. The aqueous emulsion polymerization normally
involves the polymerization in the presence of a fluorinated
surfactant, which is generally used for the stabilization of the
polymer particles formed. The suspension polymerization generally
does not involve the use of surfactant but results in substantially
larger polymer particles than in case of the aqueous emulsion
polymerization. Thus, the polymer particles in case of suspension
polymerization will quickly settle out whereas in case of
dispersions obtained in emulsion polymerization generally good
stability over a long period of time is obtained.
[0006] An aqueous emulsion polymerization wherein no surfactant is
used has been described in U.S. Pat. No. 5,453,477, WO 96/24622 and
WO 97/17381 to generally produce homo- and copolymers of
chlorotrifluoroethylene (CTFE). For example, WO 97/17381 discloses
an aqueous emulsion polymerization in the absence of a surfactant
wherein a radical initiator system of a reducing agent and
oxidizing agent is used to initiate the polymerization and whereby
the initiator system is added in one or more further charges during
the polymerization. So-called emulsifier free polymerization has
further been disclosed in WO 02/88206 and WO 02/88203. In the
latter PCT application, the use of dimethyl ether or methyl
tertiary butyl ether is taught to minimize formation of low
molecular weight fractions that may be extractable from the
fluoropolymer. WO 02/88207 teaches an emulsifier free
polymerization using certain chain transfer agents to minimize
formation of water soluble fluorinated compounds. An emulsifier
free polymerization is further disclosed in RU 2158274 for making
an elastomeric copolymer of hexafluoropropylene and vinylidene
fluoride.
[0007] Notwithstanding the fact that emulsifier free
polymerizations are known, the aqueous emulsion polymerization
process in the presence of fluorinated surfactants is still a
desirable process to produce fluoropolymers because it can yield
stable fluoropolymer particle dispersions in high yield and in a
more environmental friendly way than for example polymerizations
conducted in an organic solvent. Frequently, the emulsion
polymerization process is carried out using a perfluoroalkanoic
acid or salt thereof as a surfactant. These surfactants are
typically used as they provide a wide variety of desirable
properties such as high speed of polymerization, good
copolymerization properties of fluorinated olefins with comonomers,
small particle sizes of the resulting dispersion can be achieved,
good polymerization yields i.e. a high amount of solids can be
produced, good dispersion stability, etc. However, environmental
concerns have been raised against these surfactants and moreover
these surfactants are generally expensive.
[0008] Alternative surfactants to the perfluoroalkanoic acids or
salts thereof have also been proposed in the art for conducting the
emulsion polymerization of fluorinated monomers.
[0009] For example, surfactants of the general formula
R.sub.f--C.sub.2H.sub.4--SO.sub.3M, wherein R.sub.f represents a
perfluorinated aliphatic group and wherein M represents a cation,
have been disclosed in U.S. Pat. No. 5,789,508, U.S. Pat. No.
4,025,709, U.S. Pat. No. 5,688,884 and U.S. Pat. No. 4,380,618.
[0010] U.S. Pat. No. 5,763,552 discloses partially fluorinated
surfactants of the general formula
R.sub.f--(CH.sub.2).sub.m--R'.sub.f--COOM wherein R.sub.f
represents a perfluoroalkyl group or a perfluoroalkoxy group of 3
to 8 carbon atoms, R'.sub.f represents a perfluoroalkylene of 1 to
4 carbon atoms and m is 1-3.
[0011] U.S. Pat. No. 4,621,116 discloses perfluoroalkoxy benzene
sulphonic acids and salts thereof in the aqueous emulsion
polymerization of fluorinated monomers.
[0012] U.S. Pat. No. 3,271,341 teaches perfluoropolyethers of the
general formula:
F--(CF.sub.2).sub.m--O--[CFX--CF.sub.2--O].sub.n--CFX--COOA wherein
m is 1 to 5, X is F or CF.sub.3, A is a monovalent cation and n is
0 to 10. The perfluoropolyethers are taught as emulsifiers in the
emulsion polymerization of ethylenically unsaturated monomers.
[0013] U.S. Publication No. 2005/0090613 discloses fluorinated
polyethers of the formula:
F--(CF.sub.2).sub.m--O--[CFX--CF.sub.2--O].sub.n--CFX--COOA wherein
m is 3 to 10, X is F or a perfluoroalkyl group, n is 0, 1 or 2 and
A is the counter ion of the carboxylic anion. These polyethers are
taught as emulsifiers in the emulsion polymerization of fluorinated
olefins.
[0014] The use of perfluoropolyethers having neutral end groups in
an aqueous emulsion polymerization is disclosed in U.S. Pat. No.
4,864,006, U.S. Pat. No. 4,789,717 and EP 625526. For example U.S.
Pat. No. 4,864,006 and EP 625526 disclose the use of microemulsion
prepared from perfluoropolyethers having neutral end groups in an
aqueous emulsion polymerization of fluorinated monomers. In a
particular embodiment, a certain perfluoropolyether having
carboxylic end groups is taught to emulsify the neutral
perfluoropolyether.
[0015] EP 1,334,996 discloses certain perfluoropolyethers having
carboxylic acid groups or salts thereof at both end groups, i.e.
the perfluoropolyethers are bifunctional. The perfluoropolyethers
are taught for use in aqueous dispersions of fluoropolymers and in
the preparation of such dispersion by aqueous emulsion
polymerization.
[0016] WO 00/71590 teaches the use of a combination of
perfluoropolyether surfactants having a carboxylic acid group or
salt thereof with a fluoroalkyl carboxylic acid or sulphonic acid
or salt thereof. It is taught that the perfluoropolyether
surfactants on their own are not very powerful surfactants.
SUMMARY OF THE INVENTION
[0017] It would now be desirable to find an alternative emulsion
polymerization process in which the use of perfluoroalkanoic acids
and salts thereof as a fluorinated surfactant can be avoided. In
particular, it would be desirable to find an alternative surfactant
or dispersant, in particular one that is more environmentally
friendly, for example has a low toxicity and/or shows no or only
little bioaccumulation. It would also be desirable that the
alternative surfactant has good chemical and thermal stability
enabling polymerization over a wide range of conditions of for
example temperature and/or pressure. Desirably, the alternative
surfactant or dispersant allows for a high polymerization rate,
good dispersion stability, good yields, good copolymerization
properties and/or the possibility of obtaining a wide variety of
particle sizes including small particle sizes. The properties of
the resulting fluoropolymer should generally not be negatively
influenced and preferably would be improved. Desirably, the
resulting dispersions have good or excellent properties in coating
applications and/or impregnation of substrates, including for
example good film forming properties. It would further be desirable
that the polymerization can be carried out in a convenient and cost
effective way, preferably using equipment commonly used in the
aqueous emulsion polymerization of fluorinated monomers.
Additionally, it may be desirable to recover the alternative
surfactant or dispersant from waste water streams and/or to remove
or recover the surfactant from the dispersion subsequent to the
polymerization. Desirably, such recovery can proceed in an easy,
convenient and cost effective way.
[0018] It has been found that perfluoropolyethers of the following
formula (I) or (II) are effective in the aqueous emulsion
polymerization, even when used without the addition of other
surfactants such as perfluoroalkanoic acids and salts thereof. In
particular, the perfluoropolyether surfactants correspond to
formula (I) or (II) CF.sub.3--(OCF.sub.2).sub.m--O--CF.sub.2--X (I)
wherein m has a value of 1 to 6 and X represents a carboxylic acid
group or salt thereof;
CF.sub.3--O--(CF.sub.2).sub.3--(OCF(CF.sub.3)--CF.sub.2).sub.z--O-L-Y
(II) wherein z has a value of 0, 1, 2 or 3, L represents a divalent
linking group selected from --CF(CF.sub.3)--, --CF.sub.2-- and
--CF.sub.2CF.sub.2-- and Y represents a carboxylic acid group or
salt thereof. Examples of carboxylic acid salts include sodium,
potassium and ammonium (NH.sub.4) salts.
[0019] Thus, in one aspect, the invention relates to a method for
making a fluoropolymer comprising an aqueous emulsion
polymerization of one or more fluorinated monomers wherein said
aqueous emulsion polymerization is carried out in the presence of a
perfluoropolyether as an emulsifier, said perfluoropolyether being
selected from the group consisting of perfluoropolyethers according
to above formula (I), perfluoropolyethers according to above
formula (II) and mixtures of perfluoropolyethers according to
formula (I) and/or (II).
[0020] In a further aspect, the invention relates to an aqueous
dispersion of a fluoropolymer comprising a perfluoropolyether as an
emulsifier, said perfluoropolyether being selected from the group
consisting of perfluoropolyethers according to above formula (I),
perfluoropolyethers according to above formula (II) and mixtures of
perfluoropolyethers according to formula (I) and/or (II).
[0021] Since the aqueous emulsion polymerization can be carried out
without the need for using a perfluoroalkanoic acid, dispersions
can be readily obtained that are free of such perfluoroalkanoic
acids or salts thereof. Thus, in a further aspect, the present
invention relates to an aqueous dispersion of a fluoropolymer
comprising a perfluoropolyether selected from the group consisting
of perfluoropolyethers according to above formula (I),
perfluoropolyethers according to above formula (II) and mixtures of
perfluoropolyethers according to formula (I) and/or (II) as an
emulsifier and wherein the aqueous dispersion is free of
perfluorinated alkanoic acids or salts thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The resulting dispersions can be used in a variety of
applications including coating and impregnation of substrates.
Generally, a non-ionic surfactant should be added to the dispersion
for such applications. Accordingly, the invention in a further
aspect relates to aqueous dispersions of a fluoropolymer comprising
a perfluoropolyether selected from the group consisting of
perfluoropolyethers according to above formula (I),
perfluoropolyethers according to above formula (II) and mixtures of
perfluoropolyethers according to formula (I) and/or (II) as an
emulsifier and additionally comprising a non-ionic surfactant,
typically in an amount of 1 to 12% by weight based on the weight of
fluoropolymer solids.
[0023] The aqueous emulsion polymerization of fluorinated monomers,
including gaseous fluorinated monomers, can be conducted using one
or more perfluoropolyethers according to formula (I) and/or (II) as
emulsifier. In one particular embodiment, the polymerization may be
carried out using a perfluoropolyether or mixture of
perfluoropolyethers according to formula (I). In another
embodiment, a perfluoropolyether or mixture of perfluoropolyethers
according to formula (II) is used. In yet another embodiment, a
mixture of one or more perfluoropolyethers according to formula (I)
and one or more perfluoropolyethers according to formula (II) is
used.
[0024] Perfluoropolyethers of formula (I) are commercially
available from Anles Ltd., St. Petersburg, Russia. These compounds
may be prepared for example as described by Ershov and Popova in
Fluorine Notes 4(11), 2002. Also, these perfluoropolyethers
typically form as byproducts in the manufacturing of
hexafluoropropylene oxide by direct oxidation of
hexafluoropropylene.
[0025] Perfluoropolyethers according to formula (II) can be derived
from reactants that are also used in the manufacturing of
fluorinated vinyl ethers as described in U.S. Pat. No. 6,255,536.
Accordingly, these perfluoropolyethers can be obtained in an
economically attractive way as they can be derived from other
starting products that may be used and needed in the manufacturing
of fluoromonomers and fluoropolymers.
[0026] In accordance with the present invention, the
perfluoropolyether is used in the aqueous emulsion polymerization
of one or more fluorinated monomers, in particular gaseous
fluorinated monomers. By gaseous fluorinated monomers is meant
monomers that are present as a gas under the polymerization
conditions. In a particular embodiment, the polymerization of the
fluorinated monomers is started in the presence of the
perfluoropolyether, i.e. the polymerization is initiated in the
presence of the perfluoropolyether. The amount of
perfluoropolyether surfactant used may vary depending on desired
properties such as amount of solids, particle size etc. Generally
the amount of perfluoropolyether surfactant will be between 0.01%
by weight based on the weight of water in the polymerization and 5%
by weight, for example between 0.05% by weight and 2% by weight. A
practical range is between 0.05% by weight and 1% by weight. While
the polymerization is generally initiated in the presence of the
perfluoropolyether surfactant, it is not excluded to add further
perfluoropolyether surfactant during the polymerization although
such will generally not be necessary. Nevertheless, it may be
desirable to add certain monomer to the polymerization in the form
of an aqueous emulsion. For example, fluorinated monomers and in
particular perfluorinated co-monomers that are liquid under the
polymerization conditions may be advantageously added in the form
of an aqueous emulsion. Such emulsion of such co-monomers is
preferably prepared using the perfluoropolyether as an
emulsifier.
[0027] The aqueous emulsion polymerization may be carried out at a
temperatures between 10 to 100.degree. C., preferably 30.degree. C.
to 80.degree. C. and the pressure is typically between 2 and 30
bar, in particular 5 to 20 bar. The reaction temperature may be
varied during the polymerization to influence the molecular weight
distribution, i.e., to obtain a broad molecular weight distribution
or to obtain a bimodal or multimodal molecular weight
distribution.
[0028] The aqueous emulsion polymerization is typically initiated
by an initiator including any of the initiators known for
initiating a free radical polymerization of fluorinated monomers.
Suitable initiators include peroxides and azo compounds and redox
based initiators. Specific examples of peroxide initiators include,
hydrogen peroxide, sodium or barium peroxide, diacylperoxides such
as diacetylperoxide, disuccinyl peroxide, dipropionylperoxide,
dibutyrylperoxide, dibenzoylperoxide, benzoylacetylperoxide,
diglutaric acid peroxide and dilaurylperoxide, and further
per-acids and salts thereof such as e.g. ammonium, sodium or
potassium salts. Examples of per-acids include peracetic acid.
Esters of the peracid can be used as well and examples thereof
include tert.-butylperoxyacetate and tert.-butylperoxypivalate.
Examples of inorganic include for example ammonium-alkali- or earth
alkali salts of persulfates, permanganic or manganic acid or
manganic acids. A persulfate initiator, e.g. ammonium persulfate
(APS), can be used on its own or may be used in combination with a
reducing agent. Suitable reducing agents include bisulfites such as
for example ammonium bisulfite or sodium metabisulfite,
thiosulfates such as for example ammonium, potassium or sodium
thiosulfate, hydrazines, azodicarboxylates and azodicarboxyldiamide
(ADA). Further reducing agents that may be used include sodium
formaldehyde sulfoxylate (Rongalit.RTM.) or fluoroalkyl sulfinates
as disclosed in U.S. Pat. No. 5,285,002. The reducing agent
typically reduces the half-life time of the persulfate initiator.
Additionally, a metal salt catalyst such as for example copper,
iron or silver salts may be added. The amount of initiator may be
between 0.01% by weight (based on the fluoropolymer solids to be
produced) and 1% by weight. In one embodiment, the amount of
initiator is between 0.05 and 0.5% by weight. In another
embodiment, the amount may be between 0.05 and 0.3% by weight.
[0029] The aqueous emulsion polymerization system may further
comprise other materials, such as buffers and, if desired,
complex-formers or chain-transfer agents. Examples of chain
transfer agents that can be used include dimethyl ether, methyl
t-butyl ether, alkanes having 1 to 5 carbon atoms such as ethane,
propane and n-pentane, halogenated hydrocarbons such as CCl.sub.4,
CHCl.sub.3 and CH.sub.2Cl.sub.2 and hydrofluorocarbon compounds
such as CH.sub.2F--CF.sub.3 (R134a).
[0030] Examples of fluorinated monomers that may be polymerized
using the perfluoropolyether surfactant as an emulsifier include
partially or fully fluorinated gaseous monomers including
fluorinated olefins such as tetrafluoroethylene,
chlorotrifluoroethylene, hexafluoropropylene, vinyl fluoride,
vinylidene fluoride, partially or fully fluorinated allyl ethers
and partially or fully fluorinated vinyl ethers. The polymerization
may further involve non-fluorinated monomers such as ethylene and
propylene.
[0031] Further examples of fluorinated monomers that may be used in
the aqueous emulsion polymerization according to the invention
include those corresponding to the formula:
CF.sub.2.dbd.CF--O--R.sub.f (III) wherein R.sub.f represents a
perfluorinated aliphatic group that may contain one or more oxygen
atoms. Preferably, the perfluorovinyl ethers correspond to the
general formula:
CF.sub.2.dbd.CFO(R.sub.fO).sub.n(R'.sub.fO).sub.mR''.sub.f (IV)
wherein R.sub.f and R'.sub.f are different linear or branched
perfluoroalkylene groups of 2-6 carbon atoms, m and n are
independently 0-10, and R''.sub.f is a perfluoroalkyl group of 1-6
carbon atoms. Examples of perfluorovinyl ethers according to the
above formulas include perfluoro-2-propoxypropylvinyl ether
(PPVE-2), perfluoro-3-methoxy-n-propylvinyl ether,
perfluoro-2-methoxy-ethylvinyl ether, perfluoromethylvinyl ether
(PMVE), perfluoro-n-propylvinyl ether (PPVE-1) and
CF.sub.3--(CF.sub.2).sub.2--O--CF(CF.sub.3)--CF.sub.2--O--CF(CF.sub.3)--C-
F.sub.2--O--CF.dbd.CF.sub.2.
[0032] Still further, the polymerization may involve comonomers
that have a functional group such as for example a group capable of
participating in a peroxide cure reaction. Such functional groups
include halogens such as Br or I as well as nitrile groups.
Specific examples of such comonomers that may be listed here
include
[0033] (a) bromo- or iodo-(per)fluoroalkyl-(per)fluorovinylethers
having the formula: Z--R.sub.f--O--CX.dbd.CX.sub.2 wherein each X
may be the same or different and represents H or F, Z is Br or I,
R.sub.f is a (per)fluoroalkylene C.sub.1-C.sub.12, optionally
containing chlorine and/or ether oxygen atoms; for example:
BrCF.sub.2--O--CF.dbd.CF.sub.2,
BrCF.sub.2CF.sub.2--O--CF.dbd.CF.sub.2,
BrCF.sub.2CF.sub.2CF.sub.2--O--CF.dbd.CF.sub.2,
CF.sub.3CFBrCF.sub.2--O--CF.dbd.CF.sub.2, and the like; and
[0034] (b) bromo- or iodo containing fluoroolefins such as those
having the formula: Z'--(R.sub.f').sub.r--CX.dbd.CX.sub.2, wherein
each X independently represents H or F, Z' is Br or I, R.sub.f' is
a perfluoroalkylene C.sub.1-C.sub.12, optionally containing
chlorine atoms and r is 0 or 1; for instance:
bromotrifluoroethylene, 4-bromo-perfluorobutene-1, and the like; or
bromofluoroolefins such as 1-bromo-2,2-difluoroethylene and
4-bromo-3,3,4,4-tetrafluorobutene-1. Examples of nitrile containing
monomers that may be used include those that correspond to one of
the following formulas: CF.sub.2.dbd.CF--CF.sub.2--O--R.sub.f--CN
CF.sub.2.dbd.CFO(CF.sub.2).sub.LCN CF.sub.2.dbd.CFO
[CF.sub.2CF(CF.sub.3)O].sub.g(CF.sub.2).sub.vOCF(CF.sub.3)CN
CF.sub.2.dbd.CF [OCF.sub.2CF(CF.sub.3)].sub.kO(CF.sub.2).sub.uCN
wherein L represents an integer of 2 to 12; g represents an integer
of 0 to 4; k represents 1 or 2; v represents an integer of 0 to 6;
u represents an integer of 1 to 6, R.sub.f is a perfluoroalkylene
or a bivalent perfluoroether group. Specific examples of nitrile
containing liquid fluorinated monomers include
perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene),
CF.sub.2.dbd.CFO(CF.sub.2).sub.5CN, and
CF.sub.2.dbd.CFO(CF.sub.2).sub.3OCF(CF.sub.3)CN.
[0035] In accordance with a particular embodiment, a fluorinated
liquid may be added to the polymerization system. By the term
`liquid` is meant that the compound should be liquid at the
conditions of temperature and pressure employed in the
polymerization process. Typically the fluorinated liquid has a
boiling point of at least 50.degree. C., preferably at least
80.degree. C. at atmospheric pressure. Fluorinated liquids include
in particular highly fluorinated hydrocarbons as well as liquid
fluorinated monomers. The term `highly fluorinated` in connection
with the present invention is used to indicate compounds in which
most and preferably all hydrogen atoms have been replaced with
fluorine atoms as well as compounds wherein the majority of
hydrogen atoms have been replaced with fluorine atoms and where
most or all of the remainder of the hydrogen atoms has been
replaced with bromine, chlorine or iodine. Typically, a highly
fluorinated compound in connection with this invention will have
only few, e.g., 1 or 2 hydrogen atoms replaced by a halogen other
than fluorine and/or have only one or two hydrogen atoms remaining.
When not all hydrogen atoms are replaced by fluorine or another
halogen, i.e., the compound is not perfluorinated, the hydrogen
atoms should generally be in a position on the compound such that
substantially no chain transfer thereto occurs, i.e., such that the
compound acts as an inert in the polymerization, i.e., the compound
does not participate in the free radical polymerization. Compounds
in which all hydrogens have been replaced by fluorine and/or other
halogen atoms are herein referred to as `perfluorinated`.
[0036] Liquid and fluorinated hydrocarbon compounds that can be
used as fluorinated liquid, typically comprise between 3 and 25
carbon atoms, preferably between 5 and 20 carbon atoms and may
contain up to 2 heteroatoms selected from oxygen, sulfur or
nitrogen. Preferably the highly fluorinated hydrocarbon compound is
a perfluorinated hydrocarbon compound. Suitable perfluorinated
hydrocarbons include perfluorinated saturated linear, branched
and/or cyclic aliphatic compounds such as a perfluorinated linear,
branched or cyclic alkane; a perfluorinated aromatic compound such
as perfluorinated benzene, or perfluorinated tetradecahydro
phenanthene. It can also be a perfluorinated alkyl amine such as a
perfluorinated trialkyl amine. It can further be a perfluorinated
cyclic aliphatic, such as decalin; and preferably a heterocyclic
aliphatic compound containing oxygen or sulfur in the ring, such as
perfluoro-2-butyl tetrahydrofuran.
[0037] Specific examples of perfluorinated hydrocarbons include
perfluoro-2-butyltetrahydrofuran, perfluorodecalin,
perfluoromethyldecalin, perfluoromethylcyclohexane,
perfluoro(1,3-dimethylcyclohexane),
perfluorodimethyldecahydronaphthalene, perfluorofluorene,
perfluoro(tetradecahydrophenanthrene), perfluorotetracosane,
perfluorokerosenes, octafluoronaphthalene, oligomers of
poly(chlorotrifluoroethylene), perfluoro(trialkylamine) such as
perfluoro(tripropylamine), perfluoro(tributylamine), or
perfluoro(tripentylamine), and octafluorotoluene,
hexafluorobenzene, and commercial fluorinated solvents, such as
Fluorinert FC-75, FC-72, FC-84, FC-77, FC-40, FC-43, FC-70, FC 5312
or FZ 348 all produced by 3M Company. A suitable inert liquid and
highly fluorinated hydrocarbon compound is
C.sub.3F.sub.7--O--CF(CF.sub.3)--CF.sub.2--O--CHF--CF.sub.3. The
fluorinated liquid may also comprise liquid fluorinated monomer
alone or in combination with above described liquid fluorinated
compounds. Examples of liquid fluorinated monomers include monomers
that are liquid under the polymerization conditions and that are
selected from (per)fluorinated vinyl ethers, (per)fluorinated allyl
ethers and (per)fluorinated alkyl vinyl monomers.
[0038] When a fluorinated liquid is used, it will generally be
preferred to emulsify the fluorinated liquid. Preferably, the
fluorinated liquid is emulsified using the perfluoropolyether
surfactant. Also, when a fluorinated liquid is used in the
polymerization, it will be advantageous that at least a portion
thereof or all is provided at the start of the polymerization such
that the polymerization is initiated in the presence of the
emulsified fluorinated liquid. The use of the fluorinated liquid
may improve such properties as the rate of polymerization,
incorporation of co-monomers and may reduce the particle size
and/or improve the amount of solids that can be obtained at the end
of the polymerization.
[0039] The aqueous emulsion polymerization may be used to produce a
variety of fluoropolymers including perfluoropolymers, which have a
fully fluorinated backbone, as well as partially fluorinated
fluoropolymers. Also the aqueous emulsion polymerization may result
in melt-processible fluoropolymers as well as those that are not
melt-processible such as for example polytetrafluoroethylene and
so-called modified polytetrafluoroethylene. The polymerization
process can further yield fluoropolymers that can be cured to make
fluoroelastomers as well as fluorothermoplasts. Fluorothermoplasts
are generally fluoropolymers that have a distinct and well
noticeable melting point, typically in the range of 60 to
340.degree. C. or between 100 and 320.degree. C. They thus have a
substantial crystalline phase. Fluoropolymers that are used for
making fluoroelastomers typically are amorphous and/or have a
neglectable amount of crystallinity such that no or hardly any
melting point is discernable for these fluoropolymers.
[0040] The aqueous emulsion polymerization results in a dispersion
of the fluoropolymer in water. Generally the amount of solids of
the fluoropolymer in the dispersion directly resulting from the
polymerization will vary between 3% by weight and about 40% by
weight depending on the polymerization conditions. A typical range
is between 5 and 30% by weight. The particle size (volume average
particle size) of the fluoropolymer is typically between 50 nm and
350 nm with a typical particle size being between 100 nm and about
300 nm. The amount of perfluoropolyether according to formula (I)
and/or (II) in the resulting dispersion is typically between 0.001
and 5% by weight based on the amount of fluoropolymer solids in the
dispersion. A typical amount may be from 0.01 to 2% by weight or
from 0.02 to 1% by weight.
[0041] The fluoropolymer may be isolated from the dispersion by
coagulation if a polymer in solid form is desired. Also, depending
on the requirements of the application in which the fluoropolymer
is to be used, the fluoropolymer may be post-fluorinated so as to
convert any thermally unstable end groups into stable CF.sub.3 end
groups. The fluoropolymer may be post-fluorinated as described in
for example EP 222945. Generally, the fluoropolymer will be post
fluorinated such that the amount of end groups in the fluoropolymer
other than CF.sub.3 is less than 80 per million carbon atoms.
[0042] For coating applications, an aqueous dispersion of the
fluoropolymer is desired and hence the fluoropolymer will not need
to be separated or coagulated from the dispersion. To obtain a
fluoropolymer dispersion suitable for use in coating applications
such as for example in the impregnation of fabrics or in the
coating of metal substrates to make for example cookware, it will
generally be desired to add further stabilizing surfactants and/or
to further increase the fluoropolymer solids. For example,
non-ionic stabilizing surfactants may be added to the fluoropolymer
dispersion. Typically these will be added thereto in an amount of 1
to 12% by weight based on fluoropolymer solids. Examples of
non-ionic surfactants that may be added include
R.sup.1--O--[CH.sub.2CH.sub.2O].sub.n--[R.sup.2O].sub.m--R.sup.3
(V) wherein R.sup.1 represents an aromatic or aliphatic hydrocarbon
group having at least 8 carbon atoms, R.sup.2 represents an
alkylene having 3 carbon atoms, R.sup.3 represents hydrogen or a
C.sub.1-C.sub.3 alkyl group, n has a value of 0 to 40, m has a
value of 0 to 40 and the sum of n+m being at least 2. It will be
understood that in the above formula (V), the units indexed by n
and m may appear as blocks or they may be present in an alternating
or random configuration. Examples of non-ionic surfactants
according to formula (V) above include alkylphenol oxy ethylates
such as ethoxylated p-isooctylphenol commercially available under
the brand name TRITON.TM. such as for example TRITON.TM. X 100
wherein the number of ethoxy units is about 10 or TRITON.TM. X 114
wherein the number of ethoxy units is about 7 to 8. Still further
examples include those in which R.sup.1n the above formula (V)
represents an alkyl group of 4 to 20 carbon atoms, m is 0 and
R.sup.3 is hydrogen. An example thereof includes isotridecanol
ethoxylated with about 8 ethoxy groups and which is commercially
available as GENAPOL.RTM.X080 from Clariant GmbH. Non-ionic
surfactants according to formula (V) in which the hydrophilic part
comprises a block-copolymer of ethoxy groups and propoxy groups may
be used as well. Such non-ionic surfactants are commercially
available from Clariant GmbH under the trade designation
GENAPOL.RTM. PF 40 and GENAPOL.RTM. PF 80.
[0043] The amount of fluoropolymer solids in the dispersion may be
upconcentrated as needed or desired to an amount between 30 and 70%
by weight. Any of the known upconcentration techniques may be used
including ultrafiltration and thermal upconcentration.
[0044] The obtained fluoropolymer may be conveniently used in most
applications optionally after the addition of non-ionic surfactant
and/or upconcentration and without removing the perfluoropolyether
surfactant. Nevertheless, for reasons of for example costs, it may
be desirable to remove the perfluoropolyether from the dispersion.
It has been found that the perfluoropolyether surfactant can be
readily removed from the aqueous dispersion using an anion exchange
resin. Accordingly, a non-ionic surfactant, e.g. as disclosed above
is added to the fluoropolymer dispersion, generally in an amount of
1 to 12% by weight and the fluoropolymer dispersion is then
contacted with an anion exchange resin. Such a method is disclosed
in detail in WO 00/35971. The anion exchange process is preferably
carried out in essentially basic conditions. Accordingly, the ion
exchange resin will preferably be in the OH-- form although anions
like fluoride or sulfate may be used as well. The specific basicity
of the ion exchange resin is not very critical. Strongly basic
resins are preferred because of their higher efficiency. The
process may be carried out by feeding the fluoropolymer dispersion
through a column that contains the ion exchange resin or
alternatively, the fluoropolymer dispersion may be stirred with the
ion exchange resin and the fluoropolymer dispersion may thereafter
be isolated by filtration. The perfluoropolyether surfactant may
subsequently be recovered from the anion exchange resin by eluting
the loaded resin. A suitable mixture for eluting the anion exchange
resin is a mixture of ammonium chloride, methanol and water.
EXAMPLES
Test Methods:
[0045] The latex particle size determination was conducted by means
of dynamic light scattering with a Malvern Zetazizer 1000 HSA in
accordance to ISO/DIS 13321. Prior to the measurements, the polymer
latexes as yielded from the polymerisations were diluted with 0.001
mol/L KCl-solution, the measurement temperature was 25.degree. C.
in all cases. The reported average is the Z-average particle
diameter.
SSG
[0046] Polymer Density was measured according to ASTM4894 Method
D792.
The Polymerization
[0047] The polymerization experiments were performed in a 40 L
autoclave equipped with an impeller agitator and a baffle. The
autoclave was evacuated and than charged with 33 l of deionized
water and set to 35.degree. C. Agitation was started at 160 rpm and
in three following cycles, the vessel was evacuated and
subsequently charged with nitrogen to assure that all oxygen had
been removed. Another cleaning cycle pas performed using TFE. After
pressurizing to 0.2 MPA the TFE was released to combustion and the
reactor was evacuated again. Then 140 mmol fluorinated emulsifier
as specified in table 1 and the following materials were added: 24
mg of Cupper sulfate penta hydrate, 0.6 mg of sulphuric acid and 8
g of a 25% by weight of aqueous ammonia solution and 5.6 g of
PPVE-2 mixed with a small amount of water. Finally the reactor was
pressurized with TFE to 0.2 MPA and 50 g of HFP were added. The
reactor was than set to 1.5 MPa using TFE and 200 ml of an aqueous
initiator solution containing 187 mg of sodium sulfite and 429 mg
of ammonium peroxodisulfate was pumped into the vessel The
beginning of the polymerization is indicated by a pressure drop.
During polymerization the pressure was maintained at 1.5 MPa by
feeding TFE into the gas phase. After 3.64 kg of TFE had been
added, the monomer valve was closed. The characteristics of the
obtained polymer dispersion are summarized in table 1.
[0048] 1000 ml of this polymer dispersion was coagulated by adding
20 ml hydrochloric acid under agitation. When coagulation was
performed 100 ml of benzene were added and stirred again. After
dewatering, the latex was washed several times with deionized
water. The polymer was dried overnight at 100.degree. C. in a
vacuum oven. TABLE-US-00001 Comparative Example Example 1 Formula
C.sub.7F.sub.15COONH.sub.4
CF.sub.3OC.sub.3F.sub.6OCF(CF.sub.3)COONH.sub.4 Polymerization 81
66 Time (min.) Average Particle 103 109 Size (nm) SSG 2.148 2.154
g/cm.sup.3 Solids content (% 9.9 9.8 by weight)
* * * * *