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
  • C08F214/00—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
  • C08F214/18—Monomers containing fluorine

Definitions

• This invention pertains to a novel semi-batch emulsion polymerization process for the production of fluoroelastomers wherein a certain class of hydrocarbon anionic surfactant is employed as the dispersing agent, but not introduced to the process until a time shortly after polymerization has begun.
• Fluoroelastomers having excellent heat resistance, oil resistance, and chemical resistance have been used widely for sealing materials, containers and hoses.
• fluoroelastomers are produced in an emulsion polymerization process wherein a water-soluble polymerization initiator and a relatively large amount of surfactant are employed.
• the surfactant most often used for such processes has been ammonium perfluorooctanoate (C-8). Fluoroelastomers prepared in such processes leave the reactor in the form of a dispersion.
• U.S. Patent No. 6,512,063 B2 discloses an emulsion polymerization process for the production of fluoroelastomers wherein a hydrocarbon sulfonate is employed as the dispersing agent.
• the surfactant is present in the reactor prior to initiation of the polymerization reaction. While the process works very well for a continuous process, the polymerization rate of a semi-batch polymerization is not suitable to sustain a commercially viable polymerization process.
• hydrocarbon anionic surfactants may be used to manufacture highly fluorinated fluoroelastomers in a semi-batch process. Surfactant should not be present in the reactor before the polymerization of monomers has begun. Instead, hydrocarbon surfactant must be added to the reactor shortly after the polymerization reaction has started.
• One aspect of the present invention provides a semi-batch emulsion polymerization process for the production of fluoroelastomers, said fluoroelastomers having at least 58 weight percent fluorine, comprising: (A) charging a reactor with a quantity of an aqueous solution substantially free of surfactant;
• the present invention is directed to a semi-batch emulsion polymerization process for producing a fluoroelastomer.
• fluoroelastomer is meant an amorphous elastomeric fluoropolymer.
• the fluoropolymer may be partially fluorinated or perfluorinated, so long as it contains at least 58 percent by weight fluorine, preferably at least 64 wt.% fluorine.
• Fluoroelastomers made by the process of this invention contain between 25 to 75 weight percent, based on the weight of the fluoroelastomer, of copolymerized units of a first monomer which may be vinylidene fluoride (VF 2 ) or tetrafluoroethylene (TFE).
• VF 2 vinylidene fluoride
• TFE tetrafluoroethylene
• the remaining units in the fluoroelastomers are comprised of one or more additional copolymerized monomers, different from said first monomer, selected from the group consisting of fluorine-containing olefins, fluorine-containing vinyl ethers, hydrocarbon olefins and mixtures thereof.
• fluorine-containing olefins copolymerizable with the first monomer include, but are not limited to, vinylidene fluoride, hexafluoropropylene (HFP), tetrafluoroethylene (TFE), 1 ,2,3,3, 3-pentafluoropropene (1 -HPFP), chlorotrifluoroethylene (CTFE) and vinyl fluoride.
• the fluorine-containing vinyl ethers employed in the present invention include, but are not limited to perfluoro(alkyl vinyl) ethers.
• a preferred class of perfluoro(alkyl vinyl) ethers includes compositions of the formula
• CF 2 CFO(CF 2 CFXO) n Rf (II) where X is F or CF3, n is 0-5, and Rf is a perfluoroalkyl group of 1-6 carbon atoms.
• a most preferred class of perfluoro(alkyl vinyl) ethers includes those ethers wherein n is 0 or 1 and R f contains 1-3 carbon atoms.
• Examples of such perfluorinated ethers include perfluoro(methyl vinyl) ether (PMVE) and perfluoro(propyl vinyl) ether (PPVE).
• Other useful monomers include compounds of the formula
• the PAVE content generally ranges from 25 to 75 weight percent, based on the total weight of the fluoroelastomer. If perfluoro(methyl vinyl) ether is used, then the fluoroelastomer preferably contains between 30 and 55 wt.% copolymerized PMVE units.
• Hydrocarbon olefins useful in the fluoroelastomers prepared by the process of this invention include, but are not limited to ethylene (E) and propylene (P). If copolymerized units of a hydrocarbon olefin are present in the fluoroelastomers prepared by the process of this invention, hydrocarbon olefin content is generally 4 to 30 weight percent
• the fluoroelastomers prepared by the process of the present invention may also, optionally, comprise units of one or more cure site monomers.
• suitable cure site monomers include: i) bromine -containing olefins; ii) iodine-containing olefins; iii) bromine-containing vinyl ethers; iv) iodine-containing vinyl ethers; v) fluorine-containing olefins having a nitrile group; vi) fluorine-containing vinyl ethers having a nitrile group; vii) 1 ,1 ,3,3,3-pentafluoropropene (2-HPFP); viii) perfluoro(2- phenoxypropyl vinyl) ether; and ix) non-conjugated dienes.
• Brominated cure site monomers may contain other halogens, preferably fluorine.
• suitable iodinated cure site monomers including iodoethylene, 4- iodo-3,3,4,4-tetrafluorobutene-1 (ITFB); 3-chloro-4- iodo-3,4,4- trifluorobutene; 2-iodo -1 ,1 ,2,2-tetrafluoro-1-(vinyloxy)ethane; 2- iodo-1- (perfluorovinyloxy)-i ,1 ,-2,2-tetrafluoroethylene; 1 ,1 ⁇ .S.S.S-hexafluoro ⁇ - iodo-1-(perfluorovinyloxy)propane; 2-iodoethyl vinyl ether; 3,3,4,5,5,5- hexafluoro-4-iodopentene; and iodotrifluoroethylene are disclosed in U.S. Patent 4,694,045. AIIyI iodide and 2-iodide
• Useful nitrile-containing cure site monomers include those of the formulas shown below.
• cure site monomers are perfluorinated polyethers having a nitrile group and a trifluorovinyl ether group.
• a most preferred cure site monomer is
• CF 2 CFOCF 2 CF(CF 3 )OCF 2 CF 2 CN
• X perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) or 8-CNVE.
• non-conjugated diene cure site monomers include, but are not limited to 1 ,4-pentadiene; 1 ,5-hexadiene; 1 ,7-octadiene; 3,3,4,4-tetrafluoro-i ,5-hexadiene; and others, such as those disclosed in Canadian Patent 2,067,891 and European Patent 0784064A1.
• a suitable triene is 8-methyl-4-ethylidene-1 ,7-octadiene.
• preferred compounds for situations wherein the fluoroelastomer will be cured with peroxide, include 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB); 4-iodo-3,3,4,4- tetrafluorobutene-1 (ITFB); ally! iodide; bromotrifluoroethylene and 8- CNVE.
• BTFB 4-bromo-3,3,4,4-tetrafluorobutene-1
• ITFB 4-iodo-3,3,4,4- tetrafluorobutene-1
• ally! iodide bromotrifluoroethylene and 8- CNVE.
• 2-HPFP or perfluoro(2-phenoxypropyl vinyl) ether is the preferred cure site monomer.
• the fluoroelastomer will be cured with a tetraamine, bis(aminophenol) or bis(thioaminophenol), 8-CNVE is the preferred cure site monomer
• Units of cure site monomer when present in the fluoroelastomers manufactured by the process of this invention, are typically present at a level of 0.05-10 wt.% (based on the total weight of the monomer mixture), preferably 0.05-5 wt.% and most preferably between 0.05 and 3 wt.%.
• fluoroelastomers which may be produced by the process of this invention include, but are not limited to those having at least 58 wt.% fluorine and comprising copolymerized units of i) vinylidene fluoride and hexafluoropropylene; ii) vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene; iii) vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene and 4-bromo-3,3,4,4-tetrafluorobutene-1 ; iv) vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene and 4-iodo-3, 3,4,4- tetrafluorobutene-1 ; v) vinylidene fluoride, perfluoro(methyl vinyl) ether, tetrafluoroethylene and 4-bromo-3,3,4,4-
• iodine-containing endgroups, bromine-containing endgroups or mixtures thereof may optionally be present at one or both of the fluoroelastomer polymer chain ends as a result of the use of chain transfer or molecular weight regulating agents during preparation of the fluoroelastomers.
• the amount of chain transfer agent, when employed, is calculated to result in an iodine or bromine level in the fluoroelastomer in the range of 0.005-5 wt.%, preferably 0.05-3 wt.%.
• chain transfer agents include iodine-containing compounds that result in incorporation of bound iodine at one or both ends of the polymer molecules.
• Methylene iodide; 1 ,4-diiodoperfluoro-n-butane; and 1 ,6-diiodo-3,3,4,4,tetrafluorohexane are representative of such agents.
• iodinated chain transfer agents include 1 ,3- diiodoperfluoropropane; 1 ,6-diiodoperfluorohexane; 1 ,3-diiodo-2- chloroperfluoropropane; 1 ,2-di(iododifluoromethyl)-perfluorocyclobutane; monoiodoperfluoroethane; monoiodoperfluorobutane; 2-iodo-1- hydroperfluoroethane, etc. Also included are the cyano-iodine chain transfer agents disclosed European Patent 0868447A1. Particularly preferred are diiodinated chain transfer agents.
• brominated chain transfer agents examples include 1-bromo-2- iodoperfluoroethane; 1-bromo-3-iodoperfluoropropane; 1-iodo-2-bromo- 1 ,1-difluoroethane and others such as disclosed in U.S. Patent 5,151 ,492.
• Other chain transfer agents suitable for use in the process of this invention include those disclosed in U.S. Patent 3,707,529. Examples of such agents include isopropanol, diethylmalonate, ethyl acetate, carbon tetrachloride, acetone and dodecyl mercaptan.
• Cure site monomers and chain transfer agents may be added to the reactor neat or as solutions.
• quantities of chain transfer agent may be added throughout the entire polymerization reaction period, depending upon the desired composition of the fluoroelastomer being produced, the chain transfer agent being employed, and the total reaction time.
• R-L-M a surfactant of the formula R-L-M may be employed as the dispersing agent in the semi-batch polymerization process of this invention.
• R is an alkyl group having between 6 and 17 carbon atoms
• L is selected from the group consisting of -ArSO 3 " , -SO 3 ' , -SO 4 ' , -PO 3 ' and -COO '
• M is a univalent cation.
• - ArSO 3 ' is meant an aryl sulfonate.
• CH 3 -(CH 2 ) n - SO 3 M CH 3 -(CH 2 )n-C 6 H 4 -SO 3 M
• Surfactants of formula CH 3 -(CH 2 ) n -SO 3 M and CH 3 -(CH 2 ) n -C 6 H 4 -SO 3 M are preferred.
• Surfactant of formula CH 3 -(CH 2 ) n -SO 3 M is especially preferred.
• n is an integer from 6 to 17, preferably 7 to 14.
• the surfactant may also be a mixture of species of the same general formula, each having a different value of n.
• M is a univalent cation (e.g. H + , Na + , K + ,
• Surfactants having n values less than 6 tend to be poor soaps and poor dispersing agents for highly fluorinated fluoroelastomer latex particles. Surfactants having n values greater than 17 tend to be insufficiently soluble in water to be useful in this invention, or form insoluble salts with coagulants which are difficult to wash from fluoroelastomer crumb.
• the dispersing agent may also be a mixture of any two or more surfactants of the above general formulae.
• surfactants which may be employed in the emulsion polymerization process of the invention include, but are not limited to CH 3 - (CH 2 J 7 -SO 3 Na; and CH 3 -(CH 2 ) I iC 6 H 4 -SO 3 Na.
• the amount of surfactant to be employed in the aqueous emulsion polymerization solution is determined by balancing emulsion stability and polymerization rate with foam generation. If too little surfactant is used, excessive reactor fouling will occur and reaction rate may be undesirably slow.
• the amount of surfactant employed is typically 0.05 to 3 wt.%, based on the total weight of fluoroelastomer being produced. The preceding amounts are based on the amount of active ingredient, not on amount of a surfactant solution containing less that 100% active ingredient.
• a gaseous monomer mixture of a desired composition (initial monomer charge) is introduced into a reactor which contains an aqueous solution.
• the reactor is typically not completely filled with the aqueous solution, so that a vapor space remains.
• the aqueous solution is substantially free of surfactant until the polymerization reaction has been initiated.
• substantially free is meant less than 500 parts per million by weight (ppm) surfactant, preferably 0 ppm.
• the aqueous solution may contain a pH buffer, such as a phosphate or acetate buffer for controlling the pH of the polymerization reaction.
• a pH buffer such as a phosphate or acetate buffer
• a base such as NaOH may be used to control pH.
• pH is controlled to between 1 and 7 (preferably 3- 7), depending upon the type of fluoroelastomer being prepared.
• pH buffer or base may be added to the reactor at various times throughout the polymerization reaction, either alone or in combination with other ingredients such as polymerization initiator, liquid cure site monomer, or chain transfer agent.
• the initial aqueous solution may contain a water-soluble inorganic peroxide polymerization initiator.
• the initial aqueous solution may contain a nucleating agent, such as a fluoroelastomer seed polymer prepared previously, in order to promote fluoroelastomer latex particle formation and thus speed up the polymerization process.
• the initial monomer charge contains a quantity of a first monomer of either TFE or VF 2 and one or more additional monomers which are different from the first monomer.
• the amount of monomer mixture contained in the initial charge is set so as to result in a reactor pressure between 0.5 and 10 MPa.
• the monomer mixture is dispersed in the aqueous medium and, optionally, a chain transfer agent may also be added at this point while the reaction mixture is agitated, typically by mechanical stirring.
• a chain transfer agent may also be added at this point while the reaction mixture is agitated, typically by mechanical stirring.
• the relative amount of each monomer is dictated by reaction kinetics and is set so as to result in a fluoroelastomer having the desired ratio of copolymerized monomer units (i.e. very slow reacting monomers must be present in a higher amount relative to the other monomers than is desired in the composition of the fluoroelastomer to be produced).
• the temperature of the semi-batch reaction mixture is maintained in the range of 25 0 C - 13O 0 C, preferably 50°C - 100 0 C.
• Polymerization begins when the initiator either thermally decomposes or reacts with reducing agent and the resulting radicals react with dispersed monomer. It is important that hydrocarbon anionic surfactant be introduced to the reactor shortly after the polymerization reaction begins. The reactor must be substantially free of such surfactant prior to initiation or the polymerization rate of a semi-batch process will be drastically reduced. It is also important that surfactant be added to the reactor before the polymerization reaction has been running for too long or the fluoroelastomer dispersion becomes unstable and reactor fouling occurs.
• Additional quantities of the gaseous major monomers and cure site monomer are added at a controlled rate throughout the polymerization in order to maintain a constant reactor pressure at a controlled temperature.
• the relative ratio of monomers contained in the incremental feed is set to be approximately the same as the desired ratio of copolymerized monomer units in the resulting fluoroelastomer.
• the incremental feed contains between 25 to 75 weight percent, based on the total weight of the monomer mixture, of a first monomer of either TFE or VF 2 and 75 to 25 weight percent of one or more additional monomers that are different from the first monomer.
• Chain transfer agent may also, optionally, be introduced into the reactor at any point during this stage of the polymerization.
• additional polymerization initiator and hydrocarbon anionic surfactant are also fed to the reactor during this stage of polymerization.
• the amount of polymer formed is approximately equal to the cumulative amount of incremental monomer feed.
• the molar ratio of monomers in the incremental feed is not necessarily exactly the same as that of the desired (i.e. selected) copolymerized monomer unit composition in the resulting fluoroelastomer because the composition of the initial charge may not be exactly that required for the selected final fluoroelastomer composition, or because a portion of the monomers in the incremental feed may dissolve into the polymer particles already formed, without reacting. Polymerization times in the range of from 2 to 30 hours are typically employed in this semi-batch polymerization process.
• the polymerization temperature is maintained in the range of 25°-130°C. If the temperature is below 25 0 C, the rate of polymerization is too slow for efficient reaction on a commercial scale, while if the temperature is above 130 0 C, the reactor pressure required in order to maintain polymerization is too high to be practical.
• the polymerization pressure is controlled in the range of 0.5 to 10 MPa, preferably 1 to 6.2 MPa. In a semi-batch process, the desired polymerization pressure is initially achieved by adjusting the amount of gaseous monomers in the initial charge, and after the reaction is initiated, the pressure is adjusted by controlling the incremental gaseous monomer feed.
• the polymerization pressure is set in the above range because if it is below 1 MPa, the monomer concentration in the polymerization reaction system is too low to obtain a satisfactory reaction rate. In addition, the molecular weight does not increase sufficiently. If the pressure is above 10 MPa, the cost of the required high pressure equipment is very high.
• the amount of fluoroelastomer copolymer formed is approximately equal to the amount of incremental feed charged, and is in the range of 10-30 parts by weight of copolymer per 100 parts by weight of aqueous medium, preferably in the range of 20-25 parts by weight of the copolymer.
• the degree of copolymer formation is set in the above range because if it is less than 10 parts by weight, productivity is undesirably low, while if it is above 30 parts by weight, the solids content becomes too high for satisfactory stirring.
• Water-soluble peroxides which may be used to initiate polymerization in this invention include, for example, the ammonium, sodium or potassium salts of hydrogen persulfate.
• a reducing agent such as sodium sulfite
• water-soluble peroxides may be used alone or as a mixture of two or more types.
• the amount to be used is selected generally in the range of 0.01 to 0.4 parts by weight per 100 parts by weight of polymer, preferably 0.05 to 0.3.
• fluoroelastomer gum or crumb may be isolated from the fluoroelastomer dispersions produced by the process of this invention by the addition of a coagulating agent to the dispersion.
• a coagulating agent is chosen which forms a water- soluble salt with the surfactant contained in the dispersion. Otherwise, precipitated surfactant salt may become entrained in the isolated fluoroelastomer and then retard curing of the fluoroelastomer with bisphenol-type curatives.
• the fluoroelastomer dispersion is adjusted to a pH less than 4 and then coagulated by addition of an aluminum salt.
• Undesirable insoluble aluminum hydroxides form at pH values greater than 4.
• Aluminum salts useful as coagulating agents include, but are not limited to aluminum sulfate and alums of the general formula M'AI(SO 4 ) 2 ' 12H 2 O, wherein M' is a univalent cation, other than lithium.
• the resulting coagulated fluoroelastomer may then be filtered, washed and dried.
• common coagulants such as calcium salts (e.g. calcium nitrate) or magnesium salts (e.g. magnesium sulfate), and some salts of univalent cations (e.g. sodium chloride or potassium chloride), may be used to coagulate fluoroelastomers produced in a process employing a surfactant that forms a water soluble salt with such coagulants.
• the fluoroelastomers prepared by the process of this invention are useful in many industrial applications including seals, wire coatings, tubing and laminates.
• Inherent viscosity was measured at 30 0 C and methyl ethyl ketone was employed as solvent (0.1 g polymer in 100 ml solvent).
• solvent 0.1 g polymer in 100 ml solvent.
• a 40-liter reactor was charged with 25 liters of deionized, deoxygenated water, and 37 g of sodium phosphate dibasic heptahydrate. The reactor was heated to 80 0 C and then pressurized to 2.07 MPa with a mixture of 30.0 weight percent (wt.%) vinylidene fluoride (VF 2 ) and 70 wt. % hexafluoropropylene (HFP). A 100 ml aliquot of a solution containing 4.8 wt % sodium phosphate dibasic heptahydrate and 2 wt.% ammonium persulfate initiator was then added.
• VF 2 vinylidene fluoride
• HFP hexafluoropropylene
• a mixture of 60.0 wt.% VF 2 and 40.0 wt.% HFP was supplied to the reactor to maintain a pressure of 2.07 MPa throughout the polymerization.
• 1 ml of a 40 wt% solution of sodium octyl sulfonate (SOS) and 17.72 ml of isopropanol was added to the reactor. Every 30 minutes, an aliquot of between 0 and 10 ml of initiator solution was added in order to maintain a reaction rate of 1000 grams monomer mixture per hour.
• SOS sodium octyl sulfonate
• the fluoroelastomer was coagulated with aluminum sulfate solution. The crumb was filtered, washed with deionized water and dried. The resulting fluoroelastomer had an inherent viscosity of 0.99 dl/g, a ML(1 +10) at 121 0 C of 46 and contained 61.1wt.% VF2 and 38.9 wt.% HFP.
• SOS sodium octyl sulfonate
• a 40-liter reactor was charged with 25 liters of deionized, deoxygenated water, and 37 g of sodium phosphate dibasic heptahydrate. The reactor was heated to 80 0 C and then pressurized to 2.07 MPa with a mixture of 30.0 wt.% vinylidene fluoride (VF 2 ) and 70 wt.% hexafluoropropylene (HFP).
• VF 2 30.0 wt.% vinylidene fluoride
• HFP hexafluoropropylene
• a 100 ml aliquot of a 4.8 wt % sodium phosphate dibasic heptahydrate, 8 wt % SOS and 2 wt.% ammonium persulfate initiator solution was then added.
• a mixture of 60.0 wt.% VF 2 and 40.0 wt.% HFP was supplied to the reactor to maintain a pressure of 2.07 MPa throughout the polymerization.
• aliquots of between 0 and 10 ml of initiator solution were added every 30 minutes. After a total of 4644 g monomer mixture was supplied to the reactor and the total reaction time of 13 hours, monomer addition was discontinued and the reactor was purged of residual monomer.
• SOS sodium octyl sulfonate
• the reactor was heated to 80 0 C and then pressurized to 2.07 MPa with a mixture of 30.0 wt.% vinylidene fluoride (VF 2 ) and 70 wt.% hexafluoropropylene (HFP).
• VF 2 vinylidene fluoride
• HFP hexafluoropropylene
• a 100 ml aliquot of a 4.8 wt % sodium phosphate dibasic heptahydrate and 2 wt.% ammonium persulfate initiator solution was then added.
• a mixture of 60.0 wt.% VF 2 and 40.0 wt.% HFP was supplied to the reactor to maintain a pressure of 2.07 MPa throughout the polymerization.
• a 40-liter reactor was charged with 25 liters of deionized, deoxygenated water, and 37 g of sodium phosphate dibasic heptahydrate.
• the reactor was heated to 80 0 C and then pressurized to 2.07 MPa with a mixture of 10.0 wt.% vinylidene fluoride (VF 2 ), 80 wt.% hexafluoropropylene (HFP), and 10.0 wt.% tetrafluoroethylene (TFE).
• VF 2 vinylidene fluoride
• HFP hexafluoropropylene
• TFE 10.0 wt.% tetrafluoroethylene
• a mixture of 34.0 wt.% VF 2 , 38.0 wt.% HFP 1 and 28.0 wt % TFE was supplied to the reactor to maintain a pressure of 2.07 MPa throughout the polymerization.
• a 40 wt % SOS solution was fed to the reactor at a rate based on 0.019 ml of 40 wt.% SOS per gram of monomer mixture fed, and feeding ceased when 74.4 ml of 40 wt % SOS had been fed. Every 30 minutes, an aliquot of between 0 and 15 ml of initiator solution was added in order to maintain a reaction rate of 750 grams monomer mixture per hour.

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