Method for preparing functionalized polymers

Abstract

This invention provides compounds comprising a fluoroallyl xanthate group having formula (I). This invention also relates to a method for preparing such compounds and the use of said compounds as chain transfer agents or monomers. This invention further relates to polymers comprising units derived from compounds having formula (I), including copolymers.

Description

[Technical Field]

[0001] This invention provides compounds comprising a fluoroallyl xanthate group. The invention also relates to a method for preparing such compounds and the use of said compounds as chain transfer agents or monomers. The invention further relates to polymers comprising repeating units derived from compounds comprising a fluoroallyl xanthate group, including copolymers. Reference in Related Applications This application claims priority to European Patent Application No. 22155260.7, filed February 4, 2022, the entire contents of which are incorporated herein by reference for all purposes. [Previous Technology]

[0002] In some cases, it is beneficial to provide polymer systems containing functional groups.

[0003] Polymers with attached functional groups can be directly prepared by the polymerization of functional monomers. Oligomers and polymers prepared by controlled polymerization methods can have functionality and specific amounts of functionality at specific positions along the chain. For example, functional monomers can be periodically placed along the polymer chain, initiators can have attached functionality, or groups providing controlled polymerization can be removed and replaced with desired functional groups. However, there are several functional monomers that cannot be directly copolymerized by polymerization methods. Furthermore, using a selected polymerization method, monomers with the desired functionality may not copolymerize in the desired manner.

[0004] For example, it is very difficult to introduce a single system with functional groups of -CF2SO3H and -CF2SH side chains.

[0005] In the fields of fuel cells and electrolysis applications, obtaining polymers with ultrashort side chains containing -CF2SO3H groups will result in systems with higher electrochemical performance and better mechanical properties than current technologies, such as membranes.

[0006] The applicant has discovered a novel monomer, more specifically a monomer comprising fluoroallyl xanthate, which can be used to synthesize polymers with side functionalities that can be suitably converted into several functional groups in a post-polymerization process. The resulting polymers can be adapted to various applications.

[0007] Alkyl xanthates are compounds with the general formula ROC(=S)SR'. They are widely used in engineering fields (such as flotation) and as chain transfer agents in controlled radical polymerization, and they are usually prepared by substitution reaction of xanthates with chloroalkyl compounds. [Summary of the Invention]

[0008] Therefore, the first object of the present invention is a compound (AX) conforming to formula (I): (I) wherein Ra is (per)fluoroallyl and Rb is a straight-chain or branched alkyl group. Rb is a C1-C12 straight-chain or branched alkyl group, typically a C1-C8 straight-chain or branched alkyl group, preferably a C1-C6 straight-chain or branched alkyl group.

[0009] The present invention also relates to a method for preparing a compound (AX) according to a first purpose.

[0010] Another object of the present invention is a polymer (P) comprising repeating units derived from a compound (AX) having formula (I) as defined above.

[0011] The present invention also relates to a polymer (P) for preparing a polymer comprising repeating units of a compound (AX) having formula (I) as defined above.

[0012] The polymer (P) can be chemically transformed to convert the -S(=S)ORb groups present in the repeating units derived from the compound (AX) into different functional groups, thereby providing a further functionalized polymer.

[0013] In another object, the present invention relates to the use of a compound (AX) having formula (I) as defined above as a chain transfer agent in controlled free radical polymerization.

Implementation Method

[0014] In this application: - Any description relating to specific embodiments may be applied to and interchanged with other embodiments disclosed herein; - When an element or component is said to be included in and / or selected from the list of enumerated elements or components, it should be understood that in the relevant embodiments explicitly considered herein, the element or component may also be any one of the enumerated individual elements or components, or may also be a group consisting of any two or more of the explicitly enumerated elements or components; any element or component listed in the list of elements or components may be omitted from this list; - Any enumeration of numerical ranges by endpoints herein includes all numbers contained within the enumerated range, as well as the endpoints and equivalents of that range; - The use of parentheses "(...)" before and after the symbols or numbers in the part of the symbol or formula serves only to better distinguish the symbol or number relative to the remainder of the text; therefore, the parentheses may also be omitted.

[0015] For the purposes of this invention, the term "(per)fluoroallyl" is intended to refer to any partially or fully fluorinated allyl group, wherein all or only a portion of the hydrogen atoms of the hydrocarbon allyl structure are replaced by fluorine atoms attached to unsaturated and / or saturated carbons. When the allyl group is fully fluorinated, the term perfluorinated is used.

[0016] Ra is preferably perfluoroallyl.

[0017] The compound (AX) of the present invention preferably conforms to formula (II), wherein Rb is as defined above: (II).

[0018] Non-limiting examples of Rb notably include: ethyl, isopropyl, n-butyl, isobutyl, n-pentyl and isopentyl.

[0019] Particularly preferred are compounds having formula (III): (III), hereinafter referred to as "FAX".

[0020] The compound (AX) of the present invention can be prepared by a method comprising the steps a) and b): a) providing a xanthate having formula (IV): (IV) wherein Rb is as defined above and M+ is a monovalent cation; b) reacting the xanthate provided in step a) with a (per)fluoroallyl fluorosulfate having formula (V): Ra-OSO 2X (V) wherein Ra is a (per)fluoroallyl and X is a halogen atom.

[0021] In formula (IV), M+ is preferably selected from alkali metal cations, more preferably selected from Na+, K+, Cs+ and Li+, and even more preferably M+-K+.

[0022] Among (per)fluoroallyl fluorosulfates, perfluoroallyl fluorosulfates having the formula CF 2=CFCF 2OSO 2F (hereinafter referred to as "FAFS") are particularly preferred.

[0023] In step b), the reaction is preferably carried out at room temperature.

[0024] The reaction in step b) is typically carried out in the presence of a solvent. Suitable solvents for the reaction in step b) are polar aprotic solvents, notably glycol ethers, ethers, and nitrile solvents. Acetonitrile is preferred as the solvent.

[0025] The reaction time in step b) is appropriately included between 1 and 5 hours.

[0026] At the end of step b), the solid FSO 3M byproduct is filtered out from the reaction mixture and the compound (AX) is recovered in powder form after the solvent is evaporated.

[0027] The compound (AX) of the present invention can be used to prepare polymers. Advantageously, the repeating unit derived from the compound (AX) can serve as a precursor for other protective and / or reactive functionalities such as -CF₂SO₃H and -CF₂SH.

[0028] Therefore, another object of the present invention is a polymer (P) comprising repeating units derived from compound (AX).

[0029] The polymer (P) can be a homopolymer. That is, the polymer (P) can be composed of repeating units derived from the compound (AX).

[0030] Alternatively, the polymer (P) may be a copolymer comprising repeating units derived from the compound (AX) and repeating units derived from one or more olefinic unsaturated monomers.

[0031] The polymer (P) of the present invention is preferably a copolymer.

[0032] More preferably, the polymer (P) based copolymer comprises repeating units derived from the compound (AX) as defined above and repeating units derived from at least one fluorine monomer [fluorine monomer (FM)]. The term "fluorine monomer" is used herein in its usual sense, that is, to indicate an olefinic unsaturated monomer containing at least one fluorine atom.

[0033] In a preferred embodiment of the present invention, the polymer (P) comprises repeating units derived from compound (AX) with a total mole of 85 to 5 moles relative to the repeating units of the polymer (P) and repeating units derived from at least one fluorine monomer (FM) with a total mole of 15 to 95 moles relative to the repeating units of the polymer (P).

[0034] The polymer (P) may comprise a compound (AX) with a total mole percentage of at least 5 mol%, at least 10 mol%, at least 15 mol%, at least 20 mol%, at least 25 mol%, at least 35 mol%, at least 45 mol%, at least 50 mol%, or even at least 60 mol%, or at least 70 mol% of the repeating units relative to the polymer (P). The polymer (P) may comprise a compound (AX) with a total mole percentage of less than 80 mol%, less than 75 mol%, less than 65 mol%, and even less than 50 mol%, less than 45 mol%, or less than 30 mol% of the repeating units relative to the polymer (P). The remaining portion of the repeating units in the polymer (P) is derived from one or more fluorinated monomers (FM).

[0035] Fluorine monomers (FM) are generally selected from the following groups of composition: - C2-C8 perfluoroolefins, such as tetrafluoroethylene and hexafluoropropylene; - C2-C8 hydrogen-containing fluoroolefins, such as fluoroethylene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, pentafluoropropylene, and hexafluoroisobutylene; - (per)fluoroalkyl ethylenes conforming to the formula CH2=CH-Rf0, wherein Rf0 is a C1-C6 (per)fluoroalkyl or a C1-C6 (per)fluorooxyalkyl having one or more ether groups; - Chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins, such as chlorotrifluoroethylene; - Fluoroalkyl vinyl ethers conforming to the formula CF2=CFORf1, wherein Rf1 is a C1-C6 fluoro- or perfluoroalkyl, for example -CF3, -C2F5, -C3F7; - conforming to the formula CH2=CFOR - Hydrofluoroalkyl vinyl ethers of formula f1, wherein R f1 is a C1-C6 fluoro- or perfluoroalkyl group, such as -CF3, -C2F5, -C3F7; - Fluoro-oxyalkyl vinyl ethers conforming to formula CF2=CFOX0, wherein X0 is a C1-C12 oxyalkyl group, or a C1-C12 (per)fluorooxyalkyl group having one or more ether groups, such as perfluoro-2-propoxy-propyl; - Fluoroalkyl-methoxy-vinyl ethers conforming to formula CF2=CFOCF2OR f2, wherein R f2 is a C1-C6 fluoro- or perfluoroalkyl group, such as -CF3, -C2F5, -C3F7, or a C1-C6 (per)fluorooxyalkyl group having one or more ether groups, such as -C2F5-O-CF3; - Functional fluoroalkyl vinyl ethers conforming to formula CF2=CFOY0, wherein Y - A C1-C12 alkyl or (per)fluoroalkyl, or C1-C12 oxoalkyl or C1-C12 (per)fluorooxyalkyl, wherein the Y0 group comprises a carboxylic acid or sulfonic acid group in the form of its acid, amide, or salt; - a fluorodioxole having the following formula: wherein each Rf3, Rf4, Rf5, Rf6, being the same or different from each other, is independently a fluorine atom, a C1-C6 fluoro- or per (halo)fluoroalkyl, and contains one or more oxygen atoms as desired, such as -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3.

[0036] The polymer (P) may contain repeating units derived from at least one other monomer different from the fluorinated monomer (FM), i.e., a non-fluorinated monomer, also commonly referred to as a hydrogenated monomer [monomer (HM)]. Notable examples of hydrogenated monomers (HM) are C2-C8 nonfluorinated olefins, particularly C2-C8 nonfluorinated α-olefins, including ethylene, propylene, 1-butene; diene monomers; and styrene monomers. The monomer (HM) is preferably selected from C2-C8 α-olefins.

[0037] In a preferred embodiment of the present invention, the polymer (P) copolymer comprises repeating units derived from compounds (AX) as defined above, repeating units derived from at least one C2-C8 perfluoroolefin, and repeating units derived from at least one functional fluoro-alkyl vinyl ether having the formula CF2=CFOY0 as defined above.

[0038] C2-C8 perfluoroolefins are preferably tetrafluoroethylene. Functional fluoro-alkyl vinyl ethers having the formula CF2=CFOY0 are preferably selected from fluoro-alkyl vinyl ethers, wherein Y0 is a C1-C12 (per)fluorooxyalkyl group containing a sulfonic acid group in the form of an acid, acetic acid brine or salt.

[0039] The functional fluoroalkyl vinyl ether having the formula CF 2=CFOY 0 is preferably selected from the group consisting of: (j) sulfonyl fluoroethylene ether having the formula: CF 2=CF-O-(CF 2) m'SO 2X', wherein m' is an integer between 1 and 10, preferably between 1 and 6, more preferably between 2 and 4, and even more preferably m' equals 2; and X' is selected from halogens (Cl, F, Br, I), preferably F, or -O-M'+, wherein M'+ is selected from cations including: H+, NH 4+, K+, Li+, Na+, or mixtures thereof, preferably M'+ is H+; and (jj) sulfonyl fluorofluoroalkoxy vinyl ether having the formula: CF 2=CF-(OCF 2CF(R F1)) wO-CF 2(CF(R F2)) ySO 2X' Wherein X' is selected from halogens (Cl, F, Br, I), preferably F, or -O-M'+, wherein M'+ is selected from the following cations: H+, NH4+, K+, Li+, Na+, or mixtures thereof, preferably M'+ is H+; and wherein w is an integer between 0 and 2, RF1 and RF2 are the same or different from each other, independently of F, Cl or C1-C10 fluoroalkyl substituted with one or more ether oxygens as required, y is an integer between 0 and 6; preferably w is 1, RF1 is -CF3, y is 1 and RF2 is F.

[0040] More preferably, at least one functional fluoro-alkyl vinyl ether system is a sulfonated perfluoro vinyl ether of formula (FM1): (FM1) wherein m' is an integer between 1 and 10, preferably between 1 and 6, more preferably between 2 and 4, and X' is selected from halogens (Cl, F, Br, I), preferably F, -O-M'+, wherein M'+ is selected from the following cations: H+, NH4+, K+, Li+, Na+, or mixtures thereof, preferably M'+ is H+.

[0041] Advantageously, the sulfonated perfluorovinyl ether having formula (FM1) is selected from the group consisting of compounds having formulas (FM1-A), (FM1-B) and (FM1-C): (FM1-A) (FM1-B) (FM1-C) where X' has the same meaning as defined above.

[0042] The sulfonated perfluorovinyl ether is preferably a perfluoro-5-sulfofluoro-3-oxa-1-pentene (hereinafter referred to as "VEFS") having the formula (FM1-D): (FM1-D) It may be in the form of -SO 2F as shown above, or it may be in the form of -SO 3X, wherein X is H or an alkali metal or NH 4+.

[0043] Advantageously, the polymer (P) is a copolymer of formula (VI): (VI) where n, m, and p are independent integers greater than 0, together representing the molar fraction of each monomer in the polymer (P). Typically, n is between 0.50 and 0.75, m is between 0.10 and 0.30, and p is between 0.05 and 0.40.

[0044] In the notation of the above copolymers, the n, m, and p units can appear in any order: Formula (VI) is only intended to define the relative proportions of the monomer units, not the exact order in the copolymer (which is random). Similarly, the orientation of the repeating units in the tail-to-tail arrangement in Formula (VI) is only indicative and not intended to limit the structure of the polymer. The repeating units in the polymer (P) having Formula (VI) can be head-to-head, tail-to-tail, or head-to-tail arrangements.

[0045] In a preferred embodiment of the present invention, the polymer (P) comprises: - 5 to 25 mol% and 10 to 20 mol% of repeating units derived from compound (AX), - 45 to 85 mol% and 60 to 70 mol% of repeating units derived from tetrafluoroethylene, and - 10 to 30 mol% and 15 to 25 mol% of repeating units derived from functional fluoro-alkyl vinyl ethers having the formula (FM1-D), wherein the mol amount refers to the total mol of repeating units of the polymer (P).

[0046] The polymer (P) can be prepared by means of polymerizing a monomer mixture (MM) in the presence of at least one free radical initiator and, if desired, at least one surfactant, the monomer mixture comprising: (i) at least one compound (AX) as defined above; and (ii) at least one fluorinated monomer (FM) as defined above. The polymerization can be carried out in an aqueous emulsion.

[0047] The monomer mixture (MM) may, as needed, include: (iii) at least one monomer that is different from the fluorine monomer (FM), i.e., a monomer (HM) as defined above.

[0048] A monomer mixture (MM) comprising a compound (AX), one or more fluorinated monomers (FM) and, if desired, a monomer (HM) is generally used to prepare the polymer (P) of the present invention.

[0049] The polymerization initiator used in the method of the present invention can be organic or inorganic. Examples of organic initiators include, for instance, diisopropyl peroxide (IPP) or di- and tri-butyl peroxide (DTBP). Preferably, free radical inorganic initiators are used, such as ammonium persulfate and / or potassium persulfate and / or sodium persulfate, in combination with ferrous, copper, or silver salts as needed. The initiator feed can be added continuously or in a single step at the start of polymerization.

[0050] Surfactants may be used as needed. The surfactants may be fluorinated or non-fluorinated.

[0051] Among fluorinated surfactants, reference may be made to functional (per)fluorinated polyether compounds comprising at least one (per)fluorinated polyoxyalkylene chain and at least one functional end group selected from carboxylic acid, phosphonic acid and sulfonic acid groups, as well as cyclic fluorinated compounds, such as those described in WO 2010 / 00392.

[0052] In a typical polymerization method, at the polymerization temperature, the formation of a mixture containing water, a desired surfactant, and monomers (i), (ii), and (iii) as desired is placed in a reaction vessel; the polymerization reaction is initiated by adding a free radical initiator. In emulsion polymerization, a surfactant is typically present in the mixture, thereby forming an emulsion.

[0053] Polymerization reactions are typically carried out at temperatures ranging from 25°C to 130°C. Polymerization is typically carried out at atmospheric pressure or, for example, at pressures from 2 bar to a maximum of 60 bar.

[0054] Preferably, the polymerization reaction is carried out at a temperature in the range of 40°C-70°C, more preferably 50°C-60°C, and at a pressure of up to 20 bar, more preferably above 5 bar.

[0055] At the end of the method, a polymeric latex or suspension containing the polymer dispersed in an aqueous liquid phase is obtained. The polymer (P) can be recovered from the polymeric latex using well-known techniques (such as freeze-thaw coagulation) or by means of or addition of an electrolyte (such as aluminum sulfate or nitric acid).

[0056] Before separating the polymer (P) in powder form, the condensate can be further processed, such as purifying the latex or suspension, washing off contaminants, drying, etc.

[0057] Advantageously, the polymer (P) of the present invention is preferably obtained by a method comprising polymerizing a monomer mixture (MM) comprising a compound (AX) having formula (III) as defined above, tetrafluoroethylene, and a fluorinated monomer (FM) having formula (FM1-D). Thus, a polymer (P) having formula (VI) as defined above is obtained.

[0058] The polymer (P) according to the present invention can undergo chemical transformation.

[0059] Advantageously, the -S(=S)OR b group present in the repeating unit derived from compound (AX) can be converted into different functional groups.

[0060] In another aspect, the present invention therefore provides a method for chemically converting repeating units of a compound (AX) derived from a polymer (P) into different functional groups.

[0061] According to a first embodiment of the present invention, the method includes chemically hydrolyzing the xanthate portion of the repeating unit derived from the compound (AX), i.e. the portion having the following formula, into the group -SH.

[0062] The partial chemical hydrolysis of xanthate esters to mercapto-SH can be suitably carried out in the presence of acidic or alkaline aqueous solutions. Therefore, the method comprises reacting the polymer (P) with an acid or base in an aqueous solution.

[0063] A suitable acidic aqueous solution is noteworthy to be a solution containing HCl, HBr or H 3PO 4.

[0064] A suitable alkaline aqueous solution is noteworthy to be a solution containing NaOH or KOH.

[0065] The reaction is usually carried out at a temperature in the range of 25°C to 100°C.

[0066] The conversion of the -S(=S)OR b group into the -SH group can be observed by analytical techniques (such as infrared spectroscopy).

[0067] According to another embodiment of the present invention, the method of chemical conversion applied to polymer (P) is represented by the following: the xanthate portion of the repeating unit derived from compound (AX), i.e. the portion having the following formula, is chemically oxidized to the group -SO3H.

[0068] The partial chemical oxidation of xanthate esters to sulfonic acid groups -SO3H can be suitably carried out in the presence of an oxidizing agent such as hydrogen peroxide. Therefore, the method involves the reaction of the polymer (P) with an oxidizing agent, preferably hydrogen peroxide.

[0069] The reaction is usually carried out at a temperature in the range of 25°C to 100°C.

[0070] The conversion of the -S(=S)ORb group into the -SO3H group can be observed by analytical techniques (such as infrared spectroscopy).

[0071] Therefore, another object of the present invention is a polymer (P ox) having formula (VII): (VII) wherein: w is 0 or 1, Q is an integer between 1 and 4, preferably 1 or 2; X' is selected from halogens (Cl, F, Br, I), preferably F, or -O-M'+, wherein M'+ is selected from cations of: H+, NH4+, K+, Li+, Na+, or mixtures thereof, preferably M'+ is H+; n and p are independent integers greater than 0; m is equal to or greater than 0; m, n and p represent the molar fraction of each monomer in the polymer. Typically, n is between 0.50 and 0.75, m is between 0 and 0.30, and p is between 0.05 and 0.50. In equation (VII), n can be between 0.60 and 0.70, m between 0.10 and 0.30, and p between 0.10 and 0.20.

[0072] In a particularly preferred embodiment of the invention, a polymer (P) having formula (VI) as defined above is post-treated by chemical oxidation with hydrogen peroxide to provide a post-treated polymer (P ox) having formula (VIII): (VIII) where n, m, and p are independent integers greater than 0, representing the molar fraction of each monomer in the polymer. Typically, n is between 0.50 and 0.65, m is between 0.10 and 0.30, and p is between 0.05 and 0.40. In formula (VIII), n can be between 0.60 and 0.70, m between 0.10 and 0.30, and p between 0.10 and 0.20.

[0073] In the notation of the copolymers described above, the n, m, and p units can appear in any order: Formulas (VII) and (VIII) are intended only to define the relative proportions of the monomer units, not the exact order in the copolymer (which is random). Similarly, the orientation of the repeating units in the tail-to-tail configuration in Formulas (VII) and (VIII) is merely indicative and not intended to limit the structure of the polymer. The repeating units in polymers having Formula (VII) or (VIII) can be head-to-head, tail-to-tail, or head-to-tail arrangements.

[0074] The polymers (Pox) obtained from the methods of the present invention (such as those having formula (VII) or (VIII)) are ion-conducting polymers or their precursors. They are particularly suitable for electrochemical applications. Polymers having formula (VII) or (VIII) can be used to prepare membranes for fuel cells, membranes for electrochemical applications (e.g., chloro-soda batteries, lithium batteries). They can also be used as membranes in electrodialysis applications and reactors, where membranes made of polymers are used as superacid catalysts.

[0075] Due to the combination of chemical stability in harsh environments and good proton conductivity over a wide range of humidity conditions, perfluorinated ion-conducting polymers of sulfonic acids are considered the material benchmark today for fuel cells (primarily cryogenic fuel cells for transportation) and electrolyzers (for producing so-called green hydrogen from renewable resources). Commercially available perfluorinated ion-conducting polymers are copolymers of tetrafluoroethylene and vinyl ethers of varying lengths with -SO3H groups. Currently, the commercially available ion-conducting polymer with the shortest side chains (two -CF2- groups) is Solvay's Aquivion® ion-conducting polymer, while the ion-conducting polymer with the longest side chains is Chemours' Nafion®. Obtaining ion-conducting polymers with shorter side chains will have a significant impact on improving electrochemical performance and mechanical strength.

[0076] Therefore, the present invention provides a perfluorinated ion-conducting polymer having a side chain containing only one -CF 2- group. The polymer (P) (wherein the -S(=S)ORb group has been oxidized to a -SO 3H group, which includes polymers having formula (VII) or (VIII)) is advantageously endowed with higher proton conductivity, higher crystallinity and higher mechanical strength than commercially available perfluorinated ion-conducting polymers.

[0077] Therefore, another object of the present invention is an article comprising a polymer (P) or a polymer (Pox). This article may be in the form of a film, such as an ion-conducting membrane. Ion-conducting membranes comprising polymer (P) or advantageously comprising polymer (Pox) may be used in electrolysis applications or fuel cell applications.

[0078] In another aspect of the present invention, the use of a compound (AX) having formula (I) as defined above is provided, which is used as a chain transfer agent in controlled free radical polymerization.

[0079] In controlled radical polymerization technology, reversible addition-fragmentation chain transfer (RAFT) and macromolecular design via the exchange of xanthate compounds (MADIX) can be mentioned.

[0080] RAFT / MADIX reagents can act as reversible chain transfer agents in free radical polymerization, thereby initiating a reversible addition-fragmentation transfer reaction to create an equilibrium between the growing free radical (i.e., the growing polymer chain) and the so-called dormant substance (containing chain transfer agent fragments) that can become active again.

[0081] The applicant has unexpectedly discovered that the compound (AX) can be suitably used as a RAFT / MADIX agent in emulsion polymerization of fluorinated monomers to control the microstructure of the polymer.

[0082] Therefore, in another aspect, the present invention provides a method for emulsion polymerization of at least one fluorinated monomer, the method comprising: (i) providing at least one aqueous emulsion comprising a monomer mixture and, if desired, at least one surfactant, the monomer mixture comprising at least one fluorinated monomer [monomer (F)] and at least one compound (AX) having formula (I): (I) wherein Ra is a (per)fluoroallylic group and Rb is a straight-chain or branched alkyl group; (ii) adding at least one free radical initiator to initiate polymerization of the monomer mixture in the aqueous emulsion; (iii) continuing the polymerization by adding additional amounts of the at least one monomer (F) and / or the compound (AX) until a target amount of the monomer mixture is converted; and (iv) terminating the polymerization and recovering the latex of the fluoropolymer [polymer (F)].

[0083] The term "fluorine monomer" is used herein according to its usual meaning, that is, to indicate an alkene unsaturated monomer containing at least one fluorine atom.

[0084] It is noteworthy that the fluorine monomer (F) can be the fluorine monomer (FM) as defined above.

[0085] The method of the present invention is suitable for preparing a wide variety of fluoropolymers, including notably non-melt-processable tetrafluoroethylene polymers (including PTFE homopolymers and copolymers thereof containing low amounts of perfluorinated comonomers), thermoplastic fluoropolymers (e.g., vinylidene fluoride homopolymers and their plastic copolymers, copolymers of ethylene and trifluorochloroethylene, thermoplastic copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ethers, thermoplastic copolymers of tetrafluoroethylene and hexafluoropropylene), and fluoroelastomers.

[0086] The invention will now be described with reference to the following examples, which are merely illustrative and not intended to limit the scope of the invention. Experimental Section

[0087] Example 1: FAX Synthesis

[0088] Under nitrogen atmosphere, 109.20 g of CF₂=CFCF₂OSO₂F (FAFS) was added to a three-necked round-bottom flask equipped with a thermometer, condenser, and dropping funnel. Then, at room temperature, 70.57 g of potassium ethyl xanthate dissolved in 1482 ml of acetonitrile was added dropwise over 25 minutes. After stirring for two hours, the reaction was complete, and a white solid (FSO₃K) precipitated. The white solid was filtered, and the resulting clear solution was washed three times with distilled water (1:1 volume ratio to organic phase). The organic phase was separated and distilled under vacuum to obtain 82.73 g of pure CF₂=CFCF₂S(C=S)OCH₂CH₃ (FAX).

[0089] 19F NMR (HFMX reference) in acetone: -82 ppm (m; 2F; -SCF 2CF=CF 2); -93.5 ppm (m; 1F; cis -SCF 2CF=CF 2); -105 ppm (m; 1F; trans -SCF 2CF=CF 2); -184 ppm (m; 1F; -SCF 2CF=CF 2). 1H NMR (TMS reference) in acetone: +4.8 ppm (q; 2H; -OCH 2CH 3); +1.5 ppm (m; 3H; -OCH 2CH 3).

[0090] Example 2: Aggregation of TFE+VEFS+FAX

[0091] Deionized water (1.8 L), VEFS (212 g), and an aqueous solution of Fluorolink 7800 (540 g, 5 wt%) were charged into a 5 L reactor, pressurized with TFE at 7.5 bar, and the system was heated to 50°C with stirring. The reaction occurred after feeding a solution of potassium persulfate (concentration 10.5 g / L, 200 mL). For every 10% TFE conversion, 45 g of VEFS and a solution of VEFS (90 wt%) and FAX (10 wt%) were fed. The reaction was stopped when 4.95 g of FAX and 257 g of VEFS were added, the mixture was cooled, and the pressure was reduced by removing the TFE. The resulting polymer latex was freeze-thawed, and the polymer was recovered as a pale yellow powder.

[0092] FT-IR: 970 cm⁻¹ (combined symmetrical stretching of CF and COC); 1150 cm⁻¹ (combined asymmetric stretching of COC and stretching vibration of CF bonds); 1020 cm⁻¹ (C=S stretching); 1220 cm⁻¹ (symmetrical and asymmetric stretching of CF²); 1470 cm⁻¹ (SF bond motion); 2365 cm⁻¹ (CF harmonics / group spectrum bands); 2705 cm⁻¹ (SF harmonics).

[0093] Example 3 (Comparison): Aggregation of TFE+VEFS

[0094] Deionized water (1.8 L), VEFS (212 g), and an aqueous solution of Fluorolink 7800 (540 g, 5 wt%) were charged into a 5 L reactor, pressurized with TFE at 7.5 bar, and the system was heated to 50 °C with stirring. The reaction occurred after feeding a solution of potassium persulfate (10.5 g / L, 200 mL). 45 g of VEFS was fed for every 10% TFE conversion. When 707 g of VEFS was added, the reaction was stopped, the system was cooled, and the pressure was reduced by removing the TFE. The resulting polymer latex was freeze-thawed, and the polymer was recovered as a white powder. The powder was washed four times with demineralized water (1 L) at room temperature with stirring, and then dried overnight in a ventilated oven at 80 °C.

[0095] FT-IR: 970 cm⁻¹ (combined symmetrical stretching of CF and COC); 1150 cm⁻¹ (combined asymmetric stretching of COC and stretching vibration of CF bonds); 1220 cm⁻¹ (symmetrical and asymmetric stretching of CF 2); 1470 cm⁻¹ (SF bond motion); 2365 cm⁻¹ (CF harmonics / group spectrum bands); 2705 cm⁻¹ (SF harmonics).

[0096] Example 4: Conversion of xanthate groups to -SO3H groups

[0097] The polymer from Example 2 was washed four times with demineralized water (1 L each time) and ethyl acetate (0.5 L). The washings were carried out with stirring at room temperature. The powder was then dried overnight in a ventilated oven at 80°C. The polymer was stirred at 45°C for 8 h in a solution of H₂O₂ (15%, 200 mL) and H₂SO₄ (0.5 M, 2 mL) at a pH of approximately 4. The powder thus obtained was washed four times with distilled water (1 L each time) with stirring at room temperature, and finally dried overnight in a ventilated oven at 80°C.

[0098] FT-IR: 515 cm-1 (CS deformation of CF2-SO3); 634 cm-1 (S-OH deformation of SO3H); 970 cm-1 (Combined symmetrical stretching of CF and COC); 1057 cm-1 (Symmetrical stretching of SO3); 1154 cm-1 (Combined asymmetric stretching of COC and SO3 and stretching vibration of CF bond); 1220 cm-1 (Symmetrical and asymmetric stretching of CF2); 1300 cm-1 (Symmetrical and asymmetric stretching of SO3); 1470 cm-1 (SF bond motion); 2365 cm-1 (CF harmonic / group spectrum band); 2705 cm-1 (SF harmonic).

[0099] Example 5 (Comparison): Conversion of -SO₂F group to -SO₃H group

[0100] The polymer from Comparative Example 3 was treated with a solution of NaOH in demineralized water (20 wt%, 1 L) at 80 °C with stirring. After 8 h, the powder was washed four times with demineralized water (1 L each time) at room temperature with stirring, and then treated twice with a solution of HNO3 in distilled water (20 wt%, 1 L each time) at room temperature with stirring. The powder was washed with distilled water (4 × 1 L) at room temperature with stirring, and then dried in a ventilated oven (80 °C, overnight).

[0101] FT-IR: 515 cm⁻¹ (CS deformation of CF₂-SO₃); 634 cm⁻¹ (S-OH deformation of SO₃H); 970 cm⁻¹ (symmetric stretching of CF and COC combination); 1057 cm⁻¹ (symmetric stretching of SO₃); 1154 cm⁻¹ (asymmetric stretching of COC and SO₃ combination and tensile vibration of CF bond); 1220 cm⁻¹ (symmetric and asymmetric stretching of CF₂); 1300 cm⁻¹ (symmetric and asymmetric stretching of SO₃).

Claims

1. A compound (AX) having formula (I): (I) wherein Ra is a (per)fluorinated allyl group and Rb is a straight-chain or branched alkyl group.

2. The compound (AX) of claim 1 conforms to formula (II): (II), wherein Rb is selected from the group consisting of: ethyl, isopropyl, n-butyl, isobutyl, n-pentyl and isopentyl.

3. The compound (AX) of claim 1 or 2 has formula (III).

4. A method for preparing the compound (AX) of claim 1, the method comprising the steps a) and b): a) providing a xanthate having formula (IV) (IV) wherein Rb is a straight-chain or branched alkyl group and M+ is a monovalent cation; b) reacting the xanthate provided in step a) with a (per)fluoroallyl fluorosulfate having formula (V) Ra-OSO2X (V) wherein Ra is a (per)fluoroallyl group and X is a halogen atom.

5. As in request item 4, where, Step b) is carried out in the presence of a polar aprotic solvent.

6. A polymer (P) comprising a repeating unit (I) derived from a compound (AX) having formula (I) wherein Ra is a (per)fluoroallyl group and Rb is a straight-chain or branched alkyl group.

7. The polymer (P) of claim 6, the polymeric copolymer comprising: repeating units derived from compound (AX) and repeating units derived from at least one ethylenically unsaturated monomer [fluoromonomer (FM)] containing at least one fluorine atom.

8. The polymer (P) of claim 7, comprising repeating units derived from compound (AX) with a total mole of 85 to 5 moles relative to the repeating units of polymer (P) and repeating units derived from at least one fluorine monomer (FM) with a total mole of 15 to 95 moles relative to the repeating units of polymer (P).

9. The polymer (P) as claimed in claim 7 or 8, wherein, The fluorinated monomer (FM) is selected from the group consisting of: - C2-C8 perfluoroolefins; - C2-C8 hydrogen-containing fluoroolefins; - (per)fluoroalkylethylene conforming to the formula CH2=CH-Rf0, wherein Rf0 is a C1-C6 (per)fluoroalkyl or a C1-C6 (per)fluorooxyalkyl having one or more ether groups; - chloro- and / or bromine- and / or iodine-C2-C6 fluoroolefins; - fluoroalkylvinylether conforming to the formula CF2=CFORf1, wherein Rf1 is a C1-C6 fluoro- or perfluoroalkyl; - hydrofluoroalkylvinylether conforming to the formula CH2=CFORf1, wherein Rf1 is a C1-C6 fluoro- or perfluoroalkyl; - Fluoro-oxyalkyl vinyl ethers conforming to the formula CF2=CFOX0, wherein X0 is a C1-C12 oxyalkyl group or a C1-C12 (per)fluorooxyalkyl group having one or more ether groups; - Fluoroalkyl-methoxy-vinyl ethers conforming to the formula CF2=CFOCF2ORf2, wherein Rf2 is a C1-C6 fluoro- or perfluoroalkyl group or a C1-C6 (per)fluorooxyalkyl group having one or more ether groups; - Functional fluoro-alkyl vinyl ethers conforming to the formula CF2=CFOY0, wherein Y0 is a C1-C12 alkyl or (per)fluoroalkyl group, or a C1-C12 oxyalkyl or C1-C12 (per)fluorooxyalkyl group, wherein the Y0 group comprises a carboxylic acid or sulfonic acid group in the form of its acid, acetyl halide, or salt; - Fluorodioxole having the following formula: Each of Rf3, Rf4, Rf5, and Rf6 may be the same as or different from each other, and is independently a fluorine atom, a C1-C6 fluoro- or per(halo)fluoroalkyl group, and optionally contains one or more oxygen atoms.

10. The polymer (P) of any one of claims 6 to 8, the polymer being a copolymer comprising: repeating units derived from compound (AX), repeating units derived from at least one C2-C8 perfluoroolefin, and repeating units derived from at least one functional fluoroalkyl vinyl ether having the formula CF2=CFOY0 selected from the group consisting of: (j) a sulfonyl halide fluorovinyl ether having the formula: CF2=CF-O-(CF2)m'SO2X', wherein m' is an integer between 1 and 10; and X' is selected from halogens, -O-M'+, wherein M'+ is selected from cations of: H+, NH4+, K+, Li+, Na+, or mixtures thereof; and (jj) a sulfonyl fluoroalkoxy vinyl ether having the formula fluoroalkoxyvinylether): CF2=CF-(OCF2CF(RF1))wO-CF2(CF(RF2))ySO2X' X' is selected from halogens, -O-M'+, where M'+ is selected from the following cations: H+, NH4+, K+, Li+, Na+, or mixtures thereof; and wherein, w is an integer between 0 and 2, RF1 and RF2 are the same or different from each other, and are independently F, Cl or C1-C10 fluoroalkyl groups substituted with one or more ether oxygens as needed, and y is an integer between 0 and 6.

11. The polymer (P) as claimed in claim 10, wherein, The at least one functional fluoro-alkyl vinyl ether is selected from those having the formula (FM1): (FM1) where m' is an integer between 1 and 10, and X' is selected from halogens, -O-M'+, where M'+ is selected from the following cations: H+, NH4+, K+, Li+, Na+, or mixtures thereof.

12. The polymer (P) of any one of claims 6 to 8, comprising: - 10 to 20 mol% of repeating units derived from compound (AX), - 60 to 70 mol% of repeating units derived from tetrafluoroethylene, and - 15 to 25 mol% of repeating units derived from functional fluoro-alkyl vinyl ethers having the formula (FM1-D): (FM1-D), where the mol amount refers to the total mol of repeating units of the polymer (P).

13. A method for preparing a polymer (P) as claimed in any one of claims 6 to 12, the method comprising polymerizing a monomer mixture (MM) in the presence of at least one free radical initiator and, if desired, a surfactant, the monomer mixture comprising: (i) at least one compound (AX) as claimed in claim 1; and (ii) at least one fluorinated monomer (FM).

14. A method for chemical modification of a polymer (P) as defined in any one of claims 6 to 12, the method comprising: The xanthate moiety of the repeating unit derived from compound (AX), i.e., the moiety having the following formula: , is hydrolyzed into the group -SH.

15. As in request item 14, wherein, The hydrolysis process is carried out by reacting the polymer (P) with an acid or base in an aqueous solution.

16. A method for chemically modifying a polymer (P) as defined in any one of claims 6 to 12, the method comprising: The xanthate portion of this repeating unit derived from compound (AX), i.e., the portion having the following formula: It is oxidized to the group -SO3H.

17. As in request item 16, wherein, This oxidation process occurs through the reaction of a polymer (P) with an oxidizing agent.

18. A polymer (Pox) having formula (VII): (VII) Wherein: w is 0 or 1, Q is an integer between 1 and 4; X' is selected from halogens or -O-M'+, where M'+ is selected from the following cations: H+, NH4+, K+, Li+, Na+, or mixtures thereof; n and p are independent integers greater than 0; m is equal to or greater than 0; m, n, and p represent the molar fraction of each monomer in the polymer.

19. An article comprising a polymer (P) as claimed in any one of claims 6 to 12 or a polymer (Pox) as claimed in claim 18.

20. The product of claim 19 is a membrane used in an electrolysis cell or fuel cell.

21. The use of a compound (AX) having formula (I) as a chain transfer agent in controlled radical polymerization: (I) wherein Ra is (per)fluoroallyl and Rb is a straight-chain or branched alkyl group.