Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F14/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F14/18—Monomers containing fluorine

Definitions

• the present invention relates to the aqueous emulsion polymerization of fluorinated monomers to produce fluoropolymers.
• Fluoropolymers i.e. polymers having a fluorinated backbone
• Fluoropolymers 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.
• 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).
• PTFE polytetrafluoroethylene
• TFE tetrafluoroethylene
• HFP hexafluoropropylene
• FEP polymers perfluoroalkoxy copolymers
• ETFE ethylene-tetrafluoroethylene copolymers
• 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.
• 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.
• 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.
• emulsifier free polymerization has further been disclosed in WO 02/88206 and WO 02/88203.
• 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.
• 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.
• the emulsion polymerization process is carried out using a perfluoroalkanoic acid or salt thereof as a surfactant.
• 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.
• environmental concerns have been raised against these surfactants and moreover these surfactants are generally expensive.
• perfluoro-alkanoic acids having 8 or more carbons are known to be bioaccumulating.
• Alternative surfactants to the perfluoroalkanoic acids or salts thereof have also been proposed in the art for conducting the emulsion polymerization of fluorinated monomers.
• surfactants of the general formula R f -C 2 H 4 -SO 3 M, wherein R f represents a perfluorinated aliphatic group and wherein M represents a cation have been disclosed in U.S. Patent 5,789,508, U.S. Patent 4,025,709, U.S. Patent 5,688,884 and U.S. Patent 4,380,618.
• U.S. Patent 5,763,552 discloses partially fluorinated surfactants of the general formula R f -(CH 2 ) m -R'rCOOM wherein R f represents a perfluoroalkyl group or a perfluoroalkoxy group of 3 to 8 carbon atoms, R' f represents a perfluoroalkylene of 1 to 4 carbon atoms and m is 1-3.
• U.S. Patent 4,621, 116 discloses perfluoroalkoxy benzene sulphonic acids and salts thereof in the aqueous emulsion polymerization of fluorinated monomers.
• U.S. Patent 3,271,341 teaches perfluoropoly ethers of the general formula: F-(CF 2 ) m -O-[CFX-CF 2 -O] n -CFX-COOA wherein m is 1 to 5, X is F or CF 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.
• US Publication No. 2005/0090613 discloses fluorinated polyethers of the formula: F-(CF 2 ) m -O-[CFX-CF 2 -O] n -CFX-COOA wherein m is 3 to 10, X is F or a perfluoroalkyl group, n is O 5 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.
• perfluoropoly ethers having neutral end groups in an aqueous emulsion polymerization is disclosed in U.S. Patent 4,864,006, U.S. Patent 4,789,717 and EP 625526.
• U.S. Patent 4,864,006 and EP 625526 disclose the use of microemulsion prepared from perfiuoropolyethers having neutral end groups in an aqueous emulsion polymerization of fluorinated monomers.
• a certain perfluoropolyether having carboxylic end groups is taught to emulsify the neutral perfluoropolyether.
• EP 1,334,996 discloses certain perfiuoropolyethers having carboxylic acid groups or salts thereof at both end groups, i.e. the perfiuoropolyethers are bifunctional.
• the perfiuoropolyethers are taught for use in aqueous dispersions of fluoropolymers and in the preparation of such dispersion by aqueous emulsion polymerization.
• 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.
• WO 05/03075 discloses certain fluorinated poly ether surfactants for emulsion polymerization of fluorinated monomers.
• the alternative surfactant has good chemical and thermal stability enabling polymerization over a wide range of conditions of for example temperature and/or pressure.
• 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.
• the resulting dispersions have good or excellent properties in coating applications and/or impregnation of substrates, including for example good film forming properties.
• 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.
• perfluoro ethers of the following formula (I) are effective in the aqueous emulsion polymerization, even when used without the addition of other surfactants such as perfluoroalkanoic acids and salts thereof.
• the perfluoro ether surfactants correspond to formula (I) RrO-CF 2 CF 2 -X (I) wherein R f represents a linear or branched perfluoroalkyl group having 1 , 2, 3 or 4 carbon atoms and X represents a carboxylic acid group or salt thereof.
• carboxylic acid salts include sodium, potassium and ammonium (NH 4 ) salts.
• Perfluoro ether surfactants of formula (I) in which R f represents a perfluoroalkyl group selected from CF 3 , CF 3 CF 2 , CF 3 CF 2 CF 2 , (CF 3 ) 2 CF and (CF 3 ) 3 C are preferred as they may provide beneficial environmental properties.
• perfluoro ethers of formula (I) in which R f is CF 3 , CF 3 CF 2 or CF 3 CF 2 CF 2 eliminate more quickly from a living organism, as demonstrated on rat screening studies, than perfluoro alkanoic acids having 8 or more carbon atoms.
• 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 perfluoro ether of formula (I) as an emulsifier.
• the invention relates to an aqueous dispersion of a fluoropolymer comprising a perfluoro ether of formula (I) as an emulsifier.
• the present invention relates to an aqueous dispersion of a fluoropolymer comprising perfluoro ether of formula (I) and wherein the aqueous dispersion is free of perfluoroalkanoic acid or salts thereof.
• the resulting dispersions can be used in a variety of applications including coating and impregnation of substrates.
• a non-ionic surfactant should be added to the dispersion for such applications.
• the invention in a further aspect relates to aqueous dispersions of a fluoropolymer comprising a perfluoro ether of formula (I) 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.
• aqueous emulsion polymerization of fluorinated monomers can be conducted using one or more perfluoro ether of formula (I) as emulsifier.
• perfluoro ether surfactants include:
• the perfluoro ethers according to formula (I) can be synthesized starting from the corresponding perfluorinated acid fluorides, the preparation of which is described e.g. in WO 01/46116.
• a perfluoro ether of formula (I) in which X is a carboxylic acid the corresponding perfluorinated acid fluorides is hydrolysed with water. Conversion of the acid to any salt may be accomplished by neutralization with an appropriate base. Alternatively, the perfluorinated acid fluoride may be reacted with an alcohol (e.g. methanol or ethanol) so as to result in the corresponding ester. This ester can then be distilled for further purification and finally be saponified to the desired salt.
• an alcohol e.g. methanol or ethanol
• the perfluoro ether surfactant of formula (I) is used in the aqueous emulsion polymerization of one or more fluorinated monomers, in particular gaseous fluorinated monomers.
• gaseous fluorinated monomers monomers that are present as a gas under the polymerization conditions.
• the polymerization of the fluorinated monomers is started in the presence of the perfluoro ether surfactant, i.e. the polymerization is initiated in the presence of the perfluoro ether surfactant.
• the amount of perfluoro ether surfactant used may vary depending on desired properties such as amount of solids, particle size etc.
• the amount of perfluoro ether 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 perfluoro ether surfactant, it is not excluded to add further perfluoro ether surfactant during the polymerization although such will generally not be necessary. It may further be desirable to add certain monomer to the polymerization in the form of an aqueous emulsion.
• 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.
• aqueous emulsion polymerization may be carried out at temperatures between 10 to 100 0 C, preferably 30°C to 80°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.
• 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.
• 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.
• per-acids include peracetic acid.
• Esters of the peracid can be used as well and examples thereof include tert- butylperoxyacetate and tert.-butylperoxypivalate.
• inorganic examples 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)
• APS ammonium persulfate
• 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).
• reducing agents that may be used include sodium formaldehyde sulfoxylate (Rongalit®) or fluoroalkyl sulfmates as disclosed in U.S. Patent 5,285,002.
• the reducing agent typically reduces the half-life time of the persulfate initiator.
• 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.
• the aqueous emulsion polymerization system may further comprise other materials, such as buffers and, if desired, complex-formers or chain-transfer agents.
• chain transfer agents 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 4 , CHCl 3 and CH 2 Cl 2 and hydrofluorocarbon compounds such as CH 2 F-CF 3 (Rl 34a).
• fluorinated monomers that may be polymerized using the perfluoro ether 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.
• fluorinated monomers that may be used in the aqueous emulsion polymerization according to the invention include those corresponding to the formula:
• CF 2 CF-O-R f (II) wherein R f represents a perfluorinated aliphatic group that may contain one or more oxygen atoms.
• perfluoro vinyl ethers examples include perfluoro-2-propoxypropylvinyl ether (PPVE-2), perfluoro-3-methoxy-n-propyl vinyl ether, perfluoro-2-methoxy-ethylvinyl ether, perfluoromethylvinyl ether (PMVE), perfluoro-n- propyl vinyl ether (PPVE-I) and
• the polymerization may involve comonomers that have a functional group such as for example a group capable of participating in a peroxide cure reaction.
• 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
• 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 34O 0 C or between 100 and 32O 0 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.
• the aqueous emulsion polymerization results in a dispersion of the fluoropolymer in water.
• 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 50nm and 350nm with a typical particle size being between lOOnm and about 300nm.
• the amount of perfluoro ether of formula (I) 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.
• 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 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 3 is less than 80 per million carbon atoms.
• an aqueous dispersion of the fluoropolymer is desired and hence the fluoropolymer will not need to be separated or coagulated from the dispersion.
• 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.
• 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 ⁇ O-[CH 2 CH 2 O] n -[R 2 O] 1n -R 3 (IV) wherein R 1 represents an aromatic or aliphatic linear or branched hydrocarbon group having at least 8 carbon atoms, R 2 represents an alkylene having 3 carbon atoms, R 3 represents hydrogen or a C 1 -C 3 alkyl group, n has a value of O 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 (IV) 5 the units indexed by n and m may appear as blocks or they may be present in an alternating or random configuration.
• non-ionic surfactants include alkylphenol oxy ethylates such as ethoxylated p-isooctylphenol commercially available under the brand name TRITONTM such as for example TRITONTM X 100 wherein the number of ethoxy units is about 10 or TRITONTM X 114 wherein the number of ethoxy units is about 7 to 8.
• R 1 in the above formula (IV) represents an alkyl group of 4 to 20 carbon atoms, m is 0 and R 3 is hydrogen.
• Non-ionic surfactants according to formula (IV) 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® PF 40 and GENAPOL® PF 80.
• 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.
• the obtained fluoropolymer dispersion may be conveniently used in most applications optionally after the addition of non-ionic surfactant and/or upconcentration and without removing the perfluoro ether surfactant.
• 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-soiution, the measurement temperature was 25°C in all cases. The reported average in nm is the Z-average particle diameter.
• SSG Polymer Density was measured according to ASTM 4894-4
• Solid Content Determination of solid content was done by subjecting the latex sample to a temperature up to 250°C for 30 min.
• Example 1 and comparative example C-I In example 1 fluorinated monomers were polymerized in the presence of Compound 1 as emulsifier. Comparative example C-I was made in the same way, but using C 7 F 15 COONH 4 as emulsifier.
• 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 1 of deionized water and set to 35°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 was performed using TFE. After pressurizing to 0.2 MPa the TFE was released and the reactor was evacuated again.
• the fluorinated emulsifier as specified in table 1 was added and the following materials were added in aqueous solution: 24 mg of copper sulfate penta hydrate, 0.6 mg of sulphuric acid and 8 g of a 25 weight % aqueous ammonia solution and 5.6 g of PPVE-2.
• the reactor was pressurized with TFE to 0.2 MPa and 50 g of HFP were added.
• the reactor was then set to 1.5 MPa using TFE and 100ml of an aqueous initiator solution containing 187 mg of sodium sulfite and 100ml of an aqueous initiator solution containing 429 mg of ammonium peroxodisulfate was pumped into the vessel.
• the polymerization experiments were performed in a 40 1 kettle equipped with an impeller agitator and a baffle.
• the kettle was charged with 30 1 of deionized water and set to 35 °C; the kettle was evacuated repeatedly to remove oxygen. Agitation speed was set to 165 rpm.
• TFE tetrafluoroethylene
• HFP hexafluoropropylene
• the kettle was then set to 1.5 MPa using TFE and 100 ml of an aqueous initiator solution containing 140 mg of sodium disulfite followed by 100 ml of a solution containing 340 mg of ammonium peroxodisulfate was pumped into the reactor.
• the beginning of the polymerization was indicated by a pressure drop.
• the pressure was maintained at 1.5 MPa by feeding TFE continuously.
• the monomer valve was closed and the pressure was released.
• Table 1 The characteristics of the obtained polymer latices are summarized in table 1.
• the perfluoro ether carboxylates were evaluated for urinary clearance using a pharmacokinetic study in rats. The goal was to measure the total amount of parent compound eliminated via urinary output and estimate the rate of elimination. The study was approved by the IACUC (Institutional Animal Care and Use Committees) and was performed in 3M Company's AAALAC (Association for Assessment and Accreditation of Laboratory Animal Care) -accredited facility.
• the study utilized male Sprague Dawley rats, 6 to 8 weeks of age, and approximately 200 to 250 g body weight at study onset.
• the concentration of the parent compound or metabolites thereof were quantitatively measured via fluorine NMR on each urine sample for each animal at each time point based on internally added standards.
• T ⁇ /2 is the renal half-life and is the time required for the amount of a particular substance in a biological system to be reduced to one half of its value by biological processes when the rate of removal is approximately exponential.

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