Method for producing polyvinylidene fluoride copolymer

Abstract

This application relates to a copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from fluorinated monomer M1, having a melting temperature Tm defined by the following relationship: (154.45 - 1.9472*x) - 3 < Tm (°C) < (154.45 - 1.9472*x) + 3 (where x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer, and the melting temperature is measured by DSC according to the ASTM E794-06 standard test method). This application also relates to the use of the composition in various technical fields.

Description

Technical Field

[0001] The present invention relates to a copolymer of vinylidene fluoride and a fluorinated monomer. In particular, the present invention relates to a method for preparing the copolymer. The present invention also relates to the use of the copolymer.

Background Art

[0002] Polyvinylidene fluoride (PVDF) is a highly crystalline and chemically resistant engineering thermoplastic fluoropolymer having a typical useful temperature range from -15°C to 150°C. The glass transition temperature (Tg) of PVDF resin, which usually defines the low-temperature performance, is near -40°C. However, in practice, the useful low-temperature range of PVDF under impact applications is higher than Tg. The PVDF resin becomes increasingly brittle as it approaches its glass transition temperature, and its low-temperature impact resistance deteriorates. PVDF also loses its flexibility and becomes more rigid at these lower temperatures. The low-temperature usefulness of PVDF resin is generally recognized to be in the range of +5 to -15°C.

[0003] The low-temperature properties of PVDF can be improved by introducing a comonomer during polymer synthesis to form a PVDF copolymer. As a curable elastomer (US3,136,745) showing good low-temperature performance, a copolymer of VDF and perfluoroalkyl vinyl ether (PAVE) has been synthesized. To provide better low-temperature performance, copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) are shown in US4,07,6929 and US4,569,978. CN114163572 discloses the preparation of a core-shell vinylidene fluoride copolymer. These copolymers are formed by adding a comonomer during continuous mixed monomer feeding to form a random copolymer. The problem with these better low-temperature impact PVDF copolymers is that they also have a significantly lower melting temperature than the PVDF homopolymer, reducing their useful temperature range.

[0004] One method used to optimize the properties of PVDF copolymers is to produce copolymers by altering the monomer supply during polymerization to form an initial polymer with a high VDF monomer unit, generally exceeding 90% by weight of VDF, and then adding comonomers to the reactor when polymerization is well underway to produce the copolymer. VDF-rich polymers and copolymers, if appropriately selected and in sufficient quantities, can form separate phases, resulting in dense heterogeneous copolymers. Heterogeneous PVDF copolymers have two (or more) separate phases, one having a polyvinylidene fluoride-rich phase and the other a comonomer-rich PVDF copolymer phase. These phases can form as discontinuous structures (having dispersed rubber domains). For example, US20200407543 discloses heterogeneous compositions comprising two or more separate phases. Alternatively, heterogeneous copolymers can be produced having cocontinuous phases, i.e., two (or more) continuous phases that are closely intertwined with each other and cannot be physically separated. For example, US10,570,230 discloses a heterogeneous copolymer composition comprising two or more cocontinuous phases, wherein the cocontinuous phase comprises a) 25-50% by weight of a first cocontinuous phase comprising 90-100% by weight of vinylidene fluoride monomer units and 0-10% by weight of other fluoromonomer units, and b) 50% to 75% by weight of a second cocontinuous phase comprising 65-95% by weight of vinylidene fluoride monomer units and an effective amount of one or more comonomers selected from the group consisting of hexafluoropropylene and perfluoroalkyl vinyl ethers for phase separation of the second cocontinuous phase from the first continuous phase, and the heterogeneous copolymer composition having a melting point of 150°C to 175°C. Also, WO2022114044 discloses the preparation of a vinylidene fluoride copolymer for secondary batteries containing a large amount of hexafluoropropene. However, a large amount of hexafluoropropene can lead to the dissolution of the copolymer into the electrolyte in the secondary battery. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent No. 3,136,745 [Patent Document 2] U.S. Patent No. 4076929 [Patent Document 3] U.S. Patent No. 4569978 [Patent Document 4] Chinese Patent Application Publication No. 114163572 Specification [Patent Document 5] U.S. Patent Application Publication No. 2020 / 0407543 [Patent Document 6] U.S. Patent No. 10570230 [Patent Document 7] International Publication No. 2022 / 114044 [Overview of the project] [Problems that the invention aims to solve]

[0006] There is still a need for PVDF polymers that possess a combination of high melting point for good melt processing, improved low-temperature properties, and improved dry adhesion. The object of the present invention is to provide a composition having reasonable swelling and a high melting point in order to enhance dry adhesion and thus improve production efficiency. Surprisingly, a method has now been found for producing a copolymer that shows a good compromise between melt processability, reasonable swelling, and good adhesion properties. [Means for solving the problem]

[0007] In a first aspect, the present invention provides a copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from a fluorinated monomer M1, wherein the copolymer has a melting temperature Tm defined by the following relationship: (154.45 - 1.9472*x) - 3 <Tm(℃)<(154.45-1.9472*x)+3 (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer, and the melting temperature is measured by DSC according to the ASTM E794-06 (2018) standard test method), where the fluorinated monomer M1 is hexafluoropropene, and the weight content of hexafluoropropene based on the total weight of the copolymer is less than 11% by weight. For example, if the weight content of the fluorinated monomer M1 in the copolymer is 10% by weight, then x is 10 in the above relationship. The present invention makes it possible to prepare copolymers with the same content of the fluorinated monomer M1 that have a lower melting temperature than those obtained by other methods. The copolymer thus obtained requires a lower press temperature when used in the preparation of separators or electrodes for Li-ion batteries. However, swelling is controlled due to the low content of the fluorinated monomer M1 in the copolymer, and therefore dissolution of the copolymer in the electrolyte is avoided. Compared to other copolymers having the same fluorinated monomer M1, particularly hexafluoropropene, the copolymer of the present invention has a lower melting temperature, lower swelling in the presence of an electrolyte, and better adhesion. A weight content of hexafluoropropene of less than 11% by weight is advantageously preferred when the copolymer is used as a separator. Copolymers with an HFP content exceeding 11% by weight tend to dissolve in electrolytes used in Li-ion secondary batteries.

[0008] In preferred embodiments, the weight content of the fluorinated monomer M1 is 0.1% to 11% by weight based on the total weight of the copolymer, advantageously 0.5% to 11% by weight based on the total weight of the copolymer, preferably 1% to 11% by weight based on the total weight of the copolymer, more preferably 2% to 10.5% by weight based on the total weight of the copolymer, particularly 4% to 10% by weight based on the total weight of the copolymer, and more specifically 4.5% to 10% by weight.

[0009] In a preferred embodiment, the copolymer has a heat of fusion ΔH defined by the following relationship: (34.517 - 1.0125*x) - 2.2 < ΔH (J / g) < (34.517 - 1.0125*x) + 2.2 (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer), and the heat of fusion is determined by DSC according to the ASTM E793-06 standard test method.

[0010] In a preferred embodiment, the copolymer is of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3 R is independently selected from the group consisting of H and C1-C5 alkyl groups, where R is -NHC(CH3)2CH2C(O)CH3, -NR'R'' or -OR' (wherein R' and R'' are H and a C1-C5 alkyl group optionally substituted with one or more hydroxyl, carboxyl, thiol or amino functional groups or a 5-6 membered heterocycle containing at least one nitrogen atom in the ring). 18 It contains repeating units derived from a hydrophilic monomer M2 (selected from the group consisting of alkyl groups, independently selected from the group consisting of alkyl groups).

[0011] In preferred embodiments, the copolymer comprises repeating units derived from monomers having a functional group selected from the group consisting of carboxylic acids, carboxylic acid anhydrides, carboxylic acid esters, epoxy groups, amides, hydroxyls, carbonyls, mercaptos, sulfides, oxazolines, phenols, esters, ethers, siloxanes, sulfonic acids, sulfuric acids, phosphoric acids, or phosphonic acids.

[0012] In a preferred embodiment, the copolymer is in powder form.

[0013] In another embodiment, the present invention provides the use of the copolymer as a seed for preparing an interpenetrating polymer network.

[0014] In another aspect, the present invention provides the use of the copolymer of the present invention in a separator for lithium-ion batteries.

[0015] In another embodiment, the present invention relates to a method for preparing copolymers, a) A step of filling the reactor with an initial packing mixture containing water, a surfactant, and fluorinated monomer M1, and adding vinylidene fluoride to the reactor until the operating pressure is reached; b) A step in which polymerization is initiated by adding an initiator; c) A step of forming a copolymer by continuously supplying vinylidene fluoride and optionally an initiator until all of the vinylidene fluoride has been added to the reactor; d) The step of removing the copolymer from the reactor; e) Optionally, a step of drying the copolymer to form a powder; Includes, The present invention provides a method in which the weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method is less than 11% based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method, and the entire amount of the fluorinated monomer M1 used in the method is added to the reactor before step b).

[0016] In a preferred embodiment, the fluorinated monomer M1 is selected from the group consisting of hexafluoropropene, tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, trifluoroethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.

[0017] In a preferred embodiment, the fluorinated monomer M1 is hexafluoropropene.

[0018] In preferred embodiments, the surfactant is a nonionic or non-fluorinated surfactant, or a nonionic and non-fluorinated surfactant.

[0019] In a preferred embodiment, the surfactant comprises polyethylene glycol segments and polypropylene glycol segments and has an HLB value of from 1 to 5 and preferably a weight average molecular weight of from 2,500 to 10,000 g·mol-1.

[0020] In a preferred embodiment, the hydrophilic monomer M2 is added in any one of steps a), b) and / or c), and the hydrophilic monomer M2 has the formula R 1 R 2 C═C(R 3 ))C(O)R(I) (wherein R 1 , R 2 and R 3 are independently selected from the group consisting of H and C1-C5 alkyl, and R is -NHC(CH3)2CH2C(O)CH3, -NR’R” or -OR’ (wherein R’ and R” are H, and C1-C 18 alkyl groups optionally substituted by one or more hydroxyl, thiol or amino functional groups or a 5- to 6-membered heterocyclic ring containing at least one nitrogen atom in the ring) selected independently from the group consisting of).

[0021] In another aspect, the present invention provides an article formed from a copolymer according to the present invention.

[0022] In another aspect, the present invention provides a separator for a lithium ion battery comprising an adhesive layer on at least one side of a porous substrate, the adhesive layer comprising a copolymer according to the present invention and optionally inorganic particles.

[0023] In another aspect, the present invention provides a positive electrode composition or a negative electrode composition comprising a copolymer according to the present invention.

[0024] In another aspect, the present invention provides a coated substrate to which a copolymer according to the present invention is applied as an aqueous latex or a solvent solution.

[0025] In another aspect, the present invention provides a porous membrane comprising a copolymer according to the present invention applied as an aqueous latex or a solvent solution.

[0026] In another embodiment, the present invention provides a copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from a fluorinated monomer M1, wherein the copolymer has a melting temperature Tm defined by the following relationship: (154.45 - 1.9472*x) - 3 <Tm(℃)<(154.45-1.9472*x)+3 The copolymer has the following properties (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer, and the melting temperature is measured by DSC according to the ASTM E794-06 (2018) standard test method), where the fluorinated monomer M1 is hexafluoropropene; and the weight content of hexafluoropropene based on the total weight of the copolymer is greater than 17% by weight. The copolymer of the present invention has better processability and can be used in several applications other than as a separator for non-aqueous electrolyte Li-ion secondary batteries. For example, the copolymer can be used in solid-state batteries or in the preparation of gel-like or solid electrolytes. The present invention makes it possible to prepare copolymers with the same content of the fluorinated monomer M1, and even with a higher content of the fluorinated monomer M1, that have a lower melting temperature than those obtained by other methods.

[0027] In preferred embodiments, the weight content of the fluorinated monomer M1 is 17% to 50% by weight based on the total weight of the copolymer, preferably 18% to 45% by weight based on the total weight of the copolymer, and particularly 18% to 40% by weight based on the total weight of the copolymer.

[0028] In another embodiment, the present invention relates to a method for preparing copolymers, a) A step of filling the reactor with an initial packing mixture containing water, a nonionic and non-fluorinated surfactant, and a fluorinated monomer M1, and adding vinylidene fluoride to the reactor until the operating pressure is reached; b) A step in which polymerization is initiated by adding an initiator; c) A step of forming a copolymer by continuously supplying vinylidene fluoride and optionally an initiator until all of the vinylidene fluoride has been added to the reactor; d) The step of removing the copolymer from the reactor; e) Optionally, a step of drying the copolymer to form a powder; Includes, The present invention provides a method wherein the weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method is greater than 17% by weight based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method, the entire amount of the fluorinated monomer M1 used in the method is added to the reactor before step b), and the nonionic and nonfluorinated surfactant comprises polyethylene glycol segments and polypropylene glycol segments and has an HLB value of 1 to 5 and a weight-average molecular weight of preferably 2500 to 10000 g.mol-1.

[0029] In a preferred embodiment, the fluorinated monomer M1 is hexafluoropropene.

[0030] In a preferred embodiment, the weight content of the fluorinated monomer M1 introduced into the reactor throughout the method is 17% to 50% by weight, preferably 18% to 45% by weight, and particularly 18% to 40% by weight, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the method.

[0031] In another embodiment, the present invention provides articles formed from the copolymer of the present invention. [Brief explanation of the drawing]

[0032] [Figure 1] This is an SEM image of a copolymer obtained by a specific embodiment of the present invention. [Figure 2] This is a graph showing the melting temperature of the copolymer or comparative copolymer of the present invention as a function of the weight content (%) of fluorinated monomer M1, according to one embodiment of the present invention. [Figure 3] A graph showing the melting temperature of the copolymer of the present invention as a function of the weight content (%) of the fluorinated monomer M1 according to one embodiment of the present invention.

Mode for Carrying Out the Invention

[0033] The present invention relates to a copolymer containing repeating units derived from vinylidene fluoride and a fluorinated monomer M1. The present invention also relates to a method for forming a novel copolymer and the use of the copolymer. Unless otherwise specified, all percentages are weight percentages.

[0034] <Composition> As described above, in the first aspect of the present invention, a copolymer is provided. In a preferred embodiment, the copolymer contains at least two different types of repeating units. The copolymer of the present invention contains at least repeating units derived from vinylidene fluoride. The copolymer of the present invention further contains at least repeating units derived from the fluorinated monomer M1. The fluorinated monomer M1 is different from vinylidene fluoride. The fluorinated monomer M1 contains at least one fluorine atom. The fluorinated monomer M1 may also contain a bromine, chlorine or iodine atom.

[0035] Therefore, the copolymer of the present invention contains repeating units derived from vinylidene fluoride and repeating units derived from the fluorinated monomer M1. The copolymer has a melting temperature defined by the following relationship: (154.45 - 1.9472*x) - 3 < Tm (°C) < (154.45 - 1.9472*x) + 3 (where x is the weight content expressed as a percentage of the fluorinated monomer M1 based on the total weight of the copolymer). The melting temperature is measured by DSC according to the ASTM E794 - 06 (2018) standard test method. Preferably, the copolymer has a melting temperature defined by the following relationship: (154.45 - 1.9472*x) - 2.7 < Tm (°C) < (154.45 - 1.9472*x) + 2.7.

[0036] In another embodiment, the copolymer has a melting temperature defined by the following relationship: (160.04 - 2.5108*x) - 5.5 < Tm (°C) < (160.04 - 2.5108*x) + 5.5, preferably (160.04 - 2.5108*x) - 5 < Tm (°C) < (160.04 - 2.5108*x) + 5, more preferably (160.04 - 2.5108*x) - 4 < Tm (°C) < (160.04 - 2.5108*x) + 4, particularly (160.04 - 2.5108*x) - 3 < Tm (°C) < (160.04 - 2.5108*x) + 3, where x is the weight content expressed as a percentage of the fluorinated monomer M1 based on the total weight of the copolymer).

[0037] Compared with other known copolymers of vinylidene fluoride / fluorinated monomer, the copolymer according to the present invention provides the following advantages. That is, the lower the melting temperature, the easier the production for typical molding methods, and by reducing swelling, it is possible to improve battery efficiency. Improved adhesion can also be obtained using the copolymer of the present invention.

[0038] The weight content of the fluorinated monomer M1 in the copolymer can be 1 to 66% by weight based on the total weight of the copolymer. Advantageously, the weight content of the fluorinated monomer M1 in the copolymer is more than 1% by weight, or more than 2% by weight, or more than 3% by weight, or more than 4% by weight, or more than 5% by weight, or more than 6% by weight, or more than 7% by weight, or more than 8% by weight, or more than 9% by weight, or more than 10% by weight, or more than 11% by weight, or more than 12% by weight, or more than 13% by weight, or more than 14% by weight, or more than 15% by weight based on the total weight of the copolymer.

[0039] Advantageously, the weight content of the fluorinated monomer M1 is less than 66% by weight, or less than 64% by weight, or less than 62% by weight, or less than 60% by weight, or less than 58% by weight, or less than 56% by weight, or less than 54% by weight, or less than 52% by weight, or less than 50% by weight, or less than 48% by weight, or less than 46% by weight, or less than 44% by weight, or less than 42% by weight, or less than 40% by weight.

[0040] The weight content of fluorinated monomer M1 in the copolymer of the present invention may be within any of the above ranges.

[0041] The weight content of the fluorinated monomer M1 may be less than 11% by weight based on the total weight of the copolymer. Advantageously, the weight content of the fluorinated monomer M1 is 0.1% to 11% by weight based on the total weight of the copolymer, preferably 0.5% to 11% by weight based on the total weight of the copolymer, more preferably 1% to 11% by weight based on the total weight of the copolymer, most preferably 2% to 10.5% or 2% to 10% by weight based on the total weight of the copolymer, particularly 3% to 10% by weight based on the total weight of the copolymer, more specifically 4% to 10% by weight based on the total weight of the copolymer, and most specifically 4.5% to 10% or 4.5% to 9.5% by weight based on the total weight of the copolymer.

[0042] In another embodiment, the weight content of the fluorinated monomer M1 may be 17% to 50% by weight, preferably 18% to 45% by weight, and particularly 18% to 40% by weight, based on the total weight of the copolymer.

[0043] The weight content of the fluorinated monomer M1 may be 2 to 66% by weight based on the total weight of the copolymer, or 2% to 65% by weight based on the total weight of the copolymer, or 2% to 60% by weight based on the total weight of the copolymer, or 2% to 55% by weight based on the total weight of the copolymer, or 2% to 50% by weight based on the total weight of the copolymer, or 2% to 45% by weight based on the total weight of the copolymer, or 2% to 40% by weight based on the total weight of the copolymer, or 2% to 35% by weight based on the total weight of the copolymer, or 2% to 30% by weight based on the total weight of the copolymer, or 2% to 25% by weight based on the total weight of the copolymer, or 2% to 20% by weight based on the total weight of the copolymer, or 2% to 15% by weight based on the total weight of the copolymer.

[0044] The weight content of the fluorinated monomer M1 may be 5 to 66% by weight based on the total weight of the copolymer, or 5% to 65% by weight based on the total weight of the copolymer, or 5% to 60% by weight based on the total weight of the copolymer, or 5% to 55% by weight based on the total weight of the copolymer, or 5% to 50% by weight based on the total weight of the copolymer, or 5% to 45% by weight based on the total weight of the copolymer, or 5% to 40% by weight based on the total weight of the copolymer, or 5% to 35% by weight based on the total weight of the copolymer, or 5% to 30% by weight based on the total weight of the copolymer, or 5% to 25% by weight based on the total weight of the copolymer, or 5% to 20% by weight based on the total weight of the copolymer, or 5% to 15% by weight based on the total weight of the copolymer.

[0045] Alternatively, the weight content of the fluorinated monomer M1 may be 10 to 66% by weight based on the total weight of the copolymer, or 10% to 65% by weight based on the total weight of the copolymer, or 10% to 60% by weight based on the total weight of the copolymer, or 10% to 55% by weight based on the total weight of the copolymer, or 10% to 50% by weight based on the total weight of the copolymer, or 10% to 45% by weight based on the total weight of the copolymer, or 10% to 40% by weight based on the total weight of the copolymer, or 10% to 35% by weight based on the total weight of the copolymer, or 10% to 30% by weight based on the total weight of the copolymer.

[0046] Alternatively, the weight content of the fluorinated monomer M1 may be 15 to 66% by weight based on the total weight of the copolymer, or 15% to 65% by weight based on the total weight of the copolymer, or 15% to 60% by weight based on the total weight of the copolymer, or 15% to 55% by weight based on the total weight of the copolymer, or 15% to 50% by weight based on the total weight of the copolymer, or 15% to 45% by weight based on the total weight of the copolymer, or 15% to 40% by weight based on the total weight of the copolymer.

[0047] In preferred embodiments, the fluorinated monomer M1 is hexafluoropropene, tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, trifluoroethylene, 1,2-difluoroethylene and perfluoroalkyl vinyl ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), monomer of formula CF2=CFOCF2CF(CF3)OCF2CF2X (wherein X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H); monomer of formula CF2=CFOCF2CF2SO2F; monomer of formula F(CF2)nCH2OCF=CF2 (wherein n is 1, 2, 3, 4 or 5); and R 1 CH2OCF=CF2 monomer (where R is in the formula) 1 (where m is a hydrogen atom or F(CF2)m, and m is 1, 2, 3, or 4); Formula R 2 OCF=CH2 monomer (where R is in the formula) 2 is F(CF2)p, where p is 1, 2, 3 or 4); perfluorobutylethylene (PFBE); selected from the group consisting of trifluoropropene, hexafluoroisobutylene, perfluorobutylethylene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or mixtures thereof.

[0048] A perfluoroalkyl vinyl ether useful in the present invention has the structure:CF2=CF-O-Rf (wherein Rf is one or more perfluoroalkyl groups selected from -CF3, -CF2CF3, and -CF2CF2CF3). A preferred perfluoroalkyl vinyl ether is perfluoromethyl vinyl ether.

[0049] Among trifluoropropenes, 3,3,3-trifluoropropene is preferred. Among tetrafluoropropenes, 2,3,3,3-tetrafluoropropene and 1,3,3,3-tetrafluoropropene are preferred. Among pentafluoropropenes, 1,1,3,3,3-pentafluoropropene and 1,2,3,3,3-pentafluoropropene are preferred. Chlorofluoroethylene refers to 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene, with 1-chloro-1-fluoroethylene being preferred. Chlorotrifluoropropene refers to 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0050] Preferably, the fluorinated monomer M1 is selected from the group consisting of hexafluoropropene, tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, trifluoroethylene, and perfluoroalkyl vinyl ether or mixtures thereof.

[0051] More preferably, the fluorinated monomer M1 is selected from the group consisting of hexafluoropropene, tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, trifluoroethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether, or mixtures thereof.

[0052] In particular, the fluorinated monomer M1 is selected from the group consisting of hexafluoropropene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether, or mixtures thereof. More specifically, the fluorinated monomer M1 is selected from the group consisting of hexafluoropropene and perfluoromethyl vinyl ether, or mixtures thereof.

[0053] In a preferred embodiment, the fluorinated monomer M1 is hexafluoropropene.

[0054] The weight content of repeating units derived from vinylidene fluoride can be 40 to 99.9% by weight based on the total weight of the copolymer, and preferably 50 to 90.9% by weight based on the total weight of the copolymer.

[0055] In preferred embodiments, the weight content of repeating units derived from vinylidene fluoride is 89 to 99.9% by weight based on the total weight of the copolymer, advantageously 89 to 99.5% by weight, preferably 89 to 99% by weight, more preferably 90% to 98% by weight or 89.5 to 98% by weight based on the total weight of the copolymer, most preferably 90 to 97% by weight, particularly 90 to 96% by weight, more specifically 90 to 95.5% by weight, and most specifically 90.5 to 95.5% by weight.

[0056] In another preferred embodiment, the weight content of repeating units derived from vinylidene fluoride is 50 to 83% by weight, preferably 55 to 82% by weight, and particularly 60 to 82% by weight, based on the total weight of the copolymer.

[0057] In a preferred embodiment, the copolymer has a heat of fusion ΔH defined by the following relationship: (34.517 - 1.0125*x) - 2.2 < ΔH (J / g) < (34.517 - 1.0125*x) + 2.2; (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer), and the heat of fusion is determined by DSC according to the ASTM E794-06 (2018) standard test method. Preferably, the copolymer has a heat of fusion ΔH defined by the following relationship: (34.517 - 1.0125*x) - 1.0 < ΔH (J / g) < (34.517 - 1.0125*x) + 1.0; (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer), and the heat of fusion is determined by DSC according to the ASTM E794-06 (2018) standard test method.

[0058] In a preferred embodiment, the copolymer is heated at 232°C for 100 seconds.-1 The copolymers are measured according to ASTM method D3835 and have a melt viscosity of 1 to 50 kilopoise (kP), advantageously 1 to 40 kP, preferably 1 to 32 kP, more preferably 2 to 30 kP, particularly 3 to 25 kP, and more specifically 5 to 30 kP. Copolymers with higher molecular weights tend to be tougher and have advantages in low-temperature impact, but copolymers with lower melt viscosity are useful in some applications by enabling faster melt processing.

[0059] In one embodiment, the copolymer consists of repeating units derived from vinylidene fluoride and repeating units derived from the fluorinated monomer M1.

[0060] In one embodiment, the copolymer is optionally of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3 R is independently selected from the group consisting of H and C1-C5 alkyl groups, where R is -NHC(CH3)2CH2C(O)CH3, -NR'R'' or -OR' (wherein R' and R'' are H and a C1-C5 alkyl group optionally substituted with one or more hydroxyl, carboxyl, thiol or amino functional groups or a 5-6 membered heterocycle containing at least one nitrogen atom in the ring). 18 It contains repeating units derived from a hydrophilic monomer M2 (selected from the group consisting of alkyl groups, independently selected from the group consisting of alkyl groups).

[0061] In a preferred embodiment, the hydrophilic monomer M2 is of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3R is independently selected from the group consisting of H and C1-C5 alkyl groups, where R is -NHC(CH3)2CH2C(O)CH3, -NR'R'' or -OR' (wherein R' and R'' are H and a C1-C5 alkyl group optionally substituted with one or more hydroxyl, carboxyl, thiol or amino functional groups or a 5-6 membered heterocycle containing at least one nitrogen atom in the ring). 15 It is selected from the group consisting of alkyls (independently selected from the group consisting of alkyls). In a preferred embodiment, the hydrophilic monomer M2 is of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3 R is independently selected from the group consisting of H and C1-C5 alkyl groups, where R is -NHC(CH3)2CH2C(O)CH3, -NR'R'' or -OR' (wherein R' and R'' are H and a C1-C5 alkyl group optionally substituted with one or more hydroxyl, carboxyl, thiol or amino functional groups or a 5-6 membered heterocycle containing at least one nitrogen atom in the ring). 10 It is selected from the group consisting of alkyls (independently selected from the group consisting of alkyls). In a preferred embodiment, the hydrophilic monomer M2 is of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3 R is independently selected from the group consisting of H and C1-C5 alkyl groups, where R is -OR' (wherein R' is H and C1-C5 alkyl groups optionally substituted with one or more -OH or CO2H functional groups). 10 It is selected from the group consisting of alkyl groups). In a preferred embodiment, the hydrophilic monomer M2 is of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3R is independently selected from the group consisting of H and C1-C3 alkyl groups, where R is -OR' (wherein R' is H and C1-C3 alkyl groups optionally substituted with one or more -OH or CO2H functional groups). 10 It is selected from the group consisting of alkyl groups). In a more preferred embodiment, the hydrophilic monomer M2 is of formula R 1 R 2 C=C(R 3 )C(O)R(I)(wherein, R 1 , R 2 and R 3A is independently selected from the group consisting of H and C1-C3 alkyl groups, and R is selected from the group consisting of -OR' (wherein R' is selected from the group consisting of H and C1-C5 alkyl groups optionally substituted with one or more -OH or CO2H functional groups). In a preferred embodiment, the hydrophilic monomer M2 is acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-dodecyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, diacetone acrylamide, lauryl acrylate, n-octyl acrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate The following are selected from the group consisting of isobutyl methacrylate, t-butyl methacrylate, n-dodecyl methacrylate, amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, n-octyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxyethyl acrylate, carboxyethyl acrylate, acryloyloxyethyl succinate, and combinations thereof. Among these, alkyl acrylates having 1 to 8 carbon atoms in the alkyl group are preferred, and alkyl acrylates having 1 to 5 carbon atoms in the alkyl group are more preferred. These may be used individually or as a mixture of two or more.In a more preferred embodiment, the hydrophilic monomer M2 is acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl methacrylate, 2 - Selected from the group consisting of hydroxyethyl acrylate, carboxyethyl acrylate, acryloyloxyethyl succinate and combinations thereof, in particular, selected from the group consisting of acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, ethyl methacrylate, propyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxyethyl acrylate, carboxyethyl acrylate, acryloyloxyethyl succinate and combinations thereof. If present, the weight content of monomer M2 may be less than 5% by weight, advantageously less than 4% by weight, preferably less than 3% by weight, more preferably less than 2% by weight, and particularly less than 1% by weight.

[0062] In another embodiment, the copolymer may also optionally contain repeating units derived from monomer M3. Monomer M3 may be (A) an alkenyl compound containing a functional group, or (B) an alkenyl compound without a functional group, or a mixture thereof. Examples of the alkenyl compound containing a functional group (A) include α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, fumaric acid, crotonic acid, and itaconic acid; vinyl ester compounds such as vinyl acetate and vinyl neodecanoate; and amidated compounds such as acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, N,N-dialkylmethacrylamide, and diacetoneacrylamide. Examples of compounds include: acrylic acid esters such as 2-hydroxyethyl acrylate, N-dialkylaminoethyl acrylate, glycidyl acrylate, n-dodecyl acrylate, and fluoroalkyl acrylate; methacrylic acid esters such as dialkylaminoethyl methacrylate, fluoroalkyl methacrylate, 2-hydroxyethyl methacrylate, n-octyl methacrylate, t-butyl methacrylate, glycidyl methacrylate, and ethylene glycol dimethacrylate; maleic anhydride; and alkenyl glycidyl ether compounds such as allyl glycidyl ether. Among these, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and allyl glycidyl ether. These may be used individually or as a mixture of two or more. Examples of alkenyl compounds (B) that do not contain functional groups include conjugated dienes such as 1,3-butadiene and isoprene; divinyl hydrocarbon compounds such as divinylbenzene; and alkenyl cyanides such as acrylonitrile and methacrylonitrile. Among these, 1,3-butadiene and acrylonitrile are preferred. These may be used individually or as a mixture of two or more.

[0063] In preferred embodiments, the copolymer may further contain a surfactant comprising polyethylene glycol segments and polypropylene glycol segments in an amount of 10 ppm to 2% by weight, based on the total weight of the copolymer. Preferably, the surfactant has an HLB value of 1 to 20, particularly 1 to 5 or 10 to 15. In particular, the surfactant comprises polyethylene glycol segments and polypropylene glycol segments and has an HLB value of 1 to 5 and a weight-average molecular weight of preferably 2500 to 10000 g.mol-1, particularly 5000 to 10000 g.mol-1. Alternatively, the surfactant comprises polyethylene glycol segments and polypropylene glycol segments and has an HLB value of 10 to 15 and a weight-average molecular weight of preferably 500 to 2500 g.mol-1. In this application, the HLB value of the surfactant refers to the HLB value calculated by the Griffin method.

[0064] In one embodiment, the copolymer may contain repeating units derived from monomers having functional groups selected from the group consisting of carboxylic acids, carboxylic acid anhydrides, carboxylic acid esters, epoxy groups, amides, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenol, ester, ether, siloxane, sulfonic acid, sulfuric acid, phosphoric acid, or phosphonic acid. Functionality can be introduced, for example, using a transfer agent used during the synthesis process. The transfer agent may be a polymer having a molar mass of 20,000 g / mol or less and having functional groups selected from the following group: carboxylic acids, carboxylic acid anhydrides, carboxylic acid esters, epoxy groups, amides, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenol, ester, ether, siloxane, sulfonic acid, sulfuric acid, phosphoric acid, or phosphonic acid. An example of this type of transfer agent is an oligomer of acrylic acid. According to a preferred embodiment, the transfer agent is an oligomer of acrylic acid having a molar mass of 20,000 g / mol or less.

[0065] In a preferred embodiment, the copolymer is in powder form. The average particle size may be 0.8 μm to 150 μm, preferably 1 μm to 100 μm.

[0066] <Method for preparing copolymers> In another embodiment, a method for preparing copolymers is provided. Copolymers are conveniently prepared by emulsion polymerization, but can also be synthesized by suspension, solution, or supercritical CO2 methods.

[0067] In a preferred embodiment, this method is a) A step of filling the reactor with an initial packing mixture containing water, a surfactant, and the fluorinated monomer M1, and adding vinylidene fluoride to the reactor until the operating pressure is reached; b) A step in which polymerization is initiated by adding an initiator; c) A step of forming a copolymer by continuously supplying vinylidene fluoride and optionally an initiator until all of the vinylidene fluoride has been added to the reactor; d) The step of removing the copolymer from the reactor; e) Optionally, a step of drying the copolymer to form a powder; Includes.

[0068] Fluorinated monomer M1 is defined above in this application. The weight content of the fluorinated monomer M1 introduced into the reactor throughout the method is defined above with respect to the weight content of the fluorinated monomer M1 in the copolymer, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the method.

[0069] Preferably, the fluorinated monomer M1 is hexafluoropropene. Preferably, the weight content of the fluorinated monomer M1 introduced into the reactor throughout the method is less than 11% by weight, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the method. The weight content of the fluorinated monomer M1 introduced into the reactor throughout the method may be 0.1% to 11% by weight, preferably 0.5% to 11% by weight, more preferably 1% to 11% by weight, most preferably 2% to 10% by weight, particularly 3% to 10% by weight, more specifically 4% to 10% by weight, and most specifically 4.5% to 9.5% by weight, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the method.

[0070] Alternatively, the weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method is greater than 17% by weight, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method. The weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method may be 17% to 50% by weight, preferably 18% to 45% by weight, and particularly 18% to 40% by weight, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method.

[0071] Furthermore, the entire amount of the fluorinated monomer M1 used in this method is added to the reactor before step b). By adding all of the fluorinated monomer M1 in advance, i.e., before the start of polymerization, the copolymer obtained by this method exhibits unexpected properties as detailed in this application.

[0072] In step a) of this method, the initial filler may also contain an antifouling agent, a buffering agent, or a molecular weight modifier in any convenient order.

[0073] Useful surfactants in the present invention include halogenated and non-halogenated surfactants known to be useful for the (co)polymerization of vinylidene fluoride and perfluoroalkyl vinyl ethers. Examples of useful surfactants include partially fluorinated and fully fluorinated carboxylates described in US2,559,752; siloxane surfactants described in US6841616B2; 3-allyloxy-2-hydroxy-1-propanesulfonate surfactants described in US6869997B2; alkylsulfonate surfactants described in US20050239983A1; alkylphosphonic acids and their salts (US8124694); polyvinylphosphonic acid, polyacrylic acid and polyvinylsulfonic acid (US8,697,822); and nonionic surfactants containing polyethylene glycol, polypropylene glycol and tetramethylene glycol (US8080621, US8765890 and US8158734).

[0074] The surfactant may be nonionic or ionic, preferably nonionic.

[0075] Preferably, the copolymer formed does not contain fluorosurfactants, meaning that fluorosurfactants are not used in the manufacture or processing of the polymer. Preferably, the surfactant is a nonionic surfactant. Therefore, the surfactant is particularly nonionic and non-fluorinated.

[0076] In preferred embodiments, the surfactant comprises polyethylene glycol segments and polypropylene glycol segments. Preferably, the surfactant has an HLB value of 1 to 20, particularly 1 to 5 or 10 to 15. In particular, the surfactant comprises polyethylene glycol segments and polypropylene glycol segments and has an HLB value of 1 to 5 and a weight-average molecular weight (measured by GPC calibrated with polystyrene standards) of preferably 2500 to 10000 g.mol-1, particularly 5000 to 10000 g.mol-1. Alternatively, the surfactant comprises polyethylene glycol segments and polypropylene glycol segments and has an HLB value of 10 to 15 and a weight-average molecular weight (measured by GPC calibrated with polystyrene standards) of preferably 500 to 2500 g.mol-1. In this application, the HLB value of the surfactant refers to the HLB value calculated by the Griffin method.

[0077] The amount of surfactant packed in the reactor may be 10 ppm to 2% by weight, preferably 10 ppm to 1.5% by weight, more preferably 10 ppm to 1% by weight, relative to the total weight of monomers used, and most preferably 100 ppm to 0.2% by weight relative to the total weight of monomers used. Typically, the surfactant is added during the initial packing of the reactor, but some may be added after the reaction has started. If necessary for further stabilization, additional surfactant may be added as the reaction progresses.

[0078] Optionally, paraffinic antifouling agents may be used during polymerization. Any long-chain saturated hydrocarbon wax or oil can be used. The oil or wax is added to the reactor before the formation of the fluoropolymer in an amount sufficient to minimize the formation of polymer adhesion to the reactor components. This amount is generally proportional to the internal surface area of ​​the reactor and can vary from about 1 to about 40 mg per cm² of internal surface area. When paraffinic wax or hydrocarbon oil is used as an antifouling agent, the amount used is typically about 5 mg per cm² of internal surface area of ​​the reactor.

[0079] The polymerization reaction mixture may optionally contain a buffer to maintain a controlled pH during the polymerization reaction. The pH is typically controlled within a range of about 3 to about 8 to minimize undesirable coloration of the product. The buffers can be added all at once, at different time points, or throughout the polymerization. Suitable exemplary buffers are phosphate buffers and acetate buffers, which are well known in the art.

[0080] Molecular weight modifiers, also known as chain transfer agents, can be optionally used to adjust the molecular weight profile of the product. They can be added in a single step at the start of the reaction, gradually increasing, or continuously throughout the reaction. The amount of molecular weight modifier added to a polymerization reaction is typically about 0.05 to about 5% by weight, more typically about 0.1 to about 2% by weight, based on the total weight of monomers added to the reaction mixture. Oxygen-containing compounds such as alcohols, carbonates, ketones, esters, and ethers can function as molecular weight modifiers. Suitable examples of oxygen-containing compounds include isopropyl alcohol, acetone, ethyl acetate, and diethyl carbonate. Other classes of molecular weight modifiers include halogenated compounds such as chlorocarbons, hydrochlorocarbons, hydrofluorocarbons, chlorofluorocarbons, and hydrochlorofluorocarbons. Specific examples of halogenated molecular weight modifiers include 1-fluoroethane, trichlorofluoromethane, and 1,1-dichloro-2,2,2-trifluoroethane. Several hydrocarbons containing 2 to 5 carbon atoms, including ethane and propane as specific examples, can be used as molecular weight modifiers.

[0081] Once all the starting materials have been packed into the reactor in step a), the air can be removed from the reactor. Sufficient heat and stirring may be provided to carry out polymerization.

[0082] Vinylidene fluoride is supplied to the reactor. The reactor is brought to operating pressure with vinylidene fluoride. The pressure used for polymerization can be selected from a wide range of pressures, from 280 to 20,000 kPa, depending on the reactor's capacity, the selected initiator system, and the monomer composition used. Polymerization pressure is typically 2,000 to 11,000 kPa, most typically 2,750 to 6,900 kPa. The pressure can be adjusted during the reaction to control the process rate and molecular weight profile. The polymerization temperature can vary from 20°C to 160°C depending on the selected initiator system, typically 35°C to 130°C, most typically 65°C to 95°C. The temperature can also be adjusted during the reaction to control the process rate, initiator efficiency, and product properties.

[0083] In step b) of this method, an initiator is added to the reactor. The initiator may be one or a combination of two or more initiators known in the art to be useful for the emulsion polymerization of halogenated monomers. A suitable non-limiting class of initiators includes persulfates, peroxides, and redox systems. Examples of persulfates are sodium persulfate, potassium persulfate, or ammonium persulfate. The amount of persulfate added to the reaction mixture is typically about 0.005 to about 1.0% by weight, based on the total weight of the monomers added to the reaction mixture. Useful organic peroxides include dialkyl peroxides, alkyl hydroperoxides, peroxyesters, and peroxydicarbonates. A suitable exemplary dialkyl peroxide is di-tert-butyl peroxide. Suitable exemplary peroxyesters include tert-amyl peroxypivalate, tert-butyl peroxypivalate, and succinic acid peroxide. Suitable exemplary peroxydicarbonate initiators include di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate, which are typically added to the reaction mixture in an amount of about 0.5 to about 2.5% by weight, based on the total weight of monomers added to the reaction mixture.

[0084] The initiator may include a redox system. A “redox system” refers to a system comprising an oxidizing agent, a reducing agent, and an accelerator that optionally acts as an electron transfer medium. The accelerator is a component that can react with both the oxidizing agent and the reducing agent in different oxidation states, thereby accelerating the overall reaction. Examples of oxidizing agents include persulfates; peroxides such as hydrogen peroxide; hydroperoxides such as tert-butyl hydroperoxide and cumene hydroperoxide; and oxidizing metal salts, such as ferric sulfate and potassium permanganate. Exemplary reducing agents include sodium formaldehyde sulfoxylate; sodium or potassium salts of sulfurous acid, bisulfite, or metabisulfite; ascorbic acid; oxalic acid; and reducing metal salts. Typical accelerators include transition metal salts such as ferrous sulfate. In a redox system, the oxidizing agent and reducing agent are typically used in amounts of about 0.01 to about 0.5% by weight, based on the total weight of monomers added to the reaction mixture. When used, accelerators are typically used in amounts of about 0.005 to about 0.025% by weight, based on the total weight of the monomers added to the reaction mixture.

[0085] In a preferred embodiment, the entire amount of the fluorinated monomer M1 is added to the reactor before step b). By adding all of the fluorinated monomer M1 before the start of polymerization, the method enables the preparation of copolymers with lower melting temperatures, higher crystallinity, and less swelling in Li-ion batteries.

[0086] To maintain the reactor pressure, vinylidene fluoride is added to the reaction as needed. Further initiators may be added optionally if necessary to keep the reaction proceeding. The manner of initiator addition depends on the initiator used, the reaction temperature, and the desired molecular weight characteristics.

[0087] The amount of fluorinated monomer M1 supplied to the reactor is the amount required to obtain the copolymer defined above.

[0088] The copolymer formed by the method of the present invention has a unique form and composition, and provides a useful combination of properties.

[0089] The higher the level of fluorinated monomer M1 added initially, the better and more reasonable swelling and improved adhesion are provided compared to when the fluorinated monomer M1 is added at a later stage of polymerization. The copolymer of the present invention has a lower melting point than other copolymers produced by adding the fluorinated monomer at a later stage of polymerization.

[0090] As detailed above, the copolymer of the present invention produced by this method may also contain repeating units derived from monomer M2 or M3 as defined above. Monomers M2 and M3 can be added in steps a), b) and / or c). The content of monomers M2 and M3 added throughout the method is adapted to the desired amount of each in the copolymer thus produced.

[0091] <Use> In another aspect of the present invention, articles formed from copolymers according to the present invention are provided. The unique properties of the copolymers of the present invention make them particularly useful in several end uses. These include, but are not limited to, the wire and cable market, the oil and gas market, and the food and beverage tube market. The copolymers of the present invention can be formulated with additives commonly used in polymer formulations for specific end uses, which include, but are not limited to, plasticizers, antioxidants, flame retardants, fillers, fibers, heat stabilizers, waxes, lubricants, metal oxides, colorants, conductive fillers, antistatic agents, and antimicrobial agents.

[0092] In preferred embodiments, the articles are selected from the group consisting of jackets, primary layers, buffer layers or reinforcing members for wires or cables, filter membranes, separators or electrodes for batteries, protective layers or adhesive layers for electrodes; foams; tubes, films, sheets, rods or fibers; gaskets; umbilicals or risers for oil and gas applications; oil and gas tank liners, tubes, bags or containers for aseptic use, pharmaceutical manufacturing and distribution, food and beverage contact, and biological applications; corrosion-resistant powder coatings for metal substrates; extruded sheet linings for tank manufacturing as on metal or as double laminates; and products manufactured using the articles described herein.

[0093] In particular, a separator for lithium-ion batteries is provided. Specifically, the separator for lithium-ion batteries includes an adhesive layer on at least one side of a porous substrate, the adhesive layer comprising a copolymer or a mutually penetrating polymer network according to the present invention. The expression mutually penetrating polymer network preferably includes a semi-mutually penetrating polymer network defined as a polymer comprising one or more polymer networks and one or more linear or branched polymers characterized by penetration of the network at the molecular scale of at least one of the linear or branched macromolecules.

[0094] In one embodiment, the adhesive layer contains 50 to 99% by weight of inorganic particles based on the total weight of the polymer and inorganic particles. Preferably, the inorganic particles are BaTiO3, Pb(Zr,Ti)O3, Pb 1-x La x Zr y O3(0 <x<1、0<y<1)、PbMg3Nb 2 / 3 The material is selected from the group consisting of O3, PbTiO3, hafnia (HfO, HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, Y2O3, boehmite (y-AlO(OH)), Al2O3, TiO2, SiC, ZrO2, boron silicate, BaSO4, nanoclay, or mixtures thereof.

[0095] Preferably, the thickness of the adhesive layer on at least one side of the porous substrate is 0.5 to 10 micrometers.

[0096] The porous substrate may take the form of a membrane or a fibrous fabric. If the porous substrate is fibrous, it may be a nonwoven web that forms a porous web, for example, a web obtained by direct spinning or meltblowing (spunbond or meltblown type).

[0097] Examples of porous substrates include, but are not limited to, polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyesters, polyacetals, polyamides, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, poly(phenylene oxide), poly(phenylene sulfide), polyethylene naphthalate, or mixtures thereof. However, other heat-resistant engineering plastics may be used without particular limitation. Nonwoven fabrics made from natural or synthetic materials may also be used as the substrate for the separator. Porous substrates generally have a thickness of 1 to 50 μm and are typically films obtained by extrusion and stretching (wet or dry methods), or cast nonwovens. Porous substrates preferably have a porosity of 5% to 95%. The average size (diameter) of the pores is preferably between 0.001 and 50 μm, more preferably between 0.01 and 10 μm.

[0098] Alternatively, the copolymer of the present invention can be used as a binder for the positive or negative electrode.

[0099] In another aspect of the present invention, an electrode composition is provided. The electrode composition comprises the copolymer, conductive agent and active material of the present invention.

[0100] The conductive agent is preferably selected from the group consisting of carbon black such as acetylene black and Ketjen black; carbon fibers such as carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers; metal powders such as SUS powder and aluminum powder; or mixtures thereof.

[0101] When the electrode is the positive electrode, the active material is preferably selected from the group consisting of transition metal oxides, sulfides, phosphates, and lithium hydroxide salts. Preferably, the active material is a lithium metal phosphate, LiCoO2, or LiNi having a composition represented by LiMPO4 (where M represents Fe, Mn, Co, or Ni). x Co 1-x O2, LiMn2O2, LiNiO2, LiNi x Co y Mn z O m Li Limited x Co y Al z O m and LiNi x Mn y Al z O m The active material is selected from the group consisting of (wherein x+y+z=1, and m is an integer representing the number of oxygen atoms in the oxide that provide an electronically equilibrium molecule). More preferably, the active material is LiFePO4 and LiNi x Co y Mn z O m The active material is selected from the group consisting of (wherein x is 0.6 or greater, y is 0.2 or less, z is 0.2 or greater, x + y + z = 1, and m is an integer representing the number of oxygen atoms in the oxide that provide an electronically equilibrium molecule). In particular, the active material is LiFePO4 and LiNi x Co y Mn z O m The formula is selected from the group consisting of (wherein x is 0.8 or greater, y is 0.1 or less, z is 0.1 or greater, x + y + z = 1, and m is an integer representing the number of oxygen atoms in the oxide that provide an electronically equilibrium molecule).

[0102] When the electrode is the negative electrode, the active material is a carbon-based material such as graphite-based carbon, coke-based carbon and hard carbon, silicon, lithium alloy, metal oxide, silicon and Li4Ti5O 12 It is preferable to select from the group consisting of alloys of the following:

[0103] The electrode composition may further contain a solvent such as water or an organic solvent.

[0104] The organic solvent is preferably selected from the group consisting of n-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), triethyl phosphite (TEP), acetone, cyclopentanone, tetrahydrofuran, methyl ethyl ketone (MEK), methyl isobutyl ketone (MiBK), ethyl acetate (EA), butyl acetate (BA), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), gamma butyrolactone, and N-butylpyrrolidone, as well as combinations thereof.

[0105] Electrode compositions are typically prepared by mixing components, namely copolymers, active materials, conductive agents, and optionally solvents. When the components are mixed in the presence of an organic solvent, the copolymer is preferably in powder form.

[0106] In another aspect of the present invention, an electrode is provided. The electrode comprises a current collector and the electrode composition according to the present invention disposed on at least one surface of the current collector. Once the electrode composition is disposed on at least one surface of the current collector, the electrode is dried to remove organic solvents or water.

[0107] According to a preferred embodiment, after evaporation of the organic solvent or water, the electrode composition cast onto the current collector has the following mass composition: a. 80% to 99.9%, preferably 80% to 99% active material. b. 0.05% to 10%, preferably 10% to 0.5% conductive agent, c. 0.05% to 10%, preferably 10% to 0.5%, of the copolymer of the present invention; It has all of these percentages, and the sum of all these percentages is 100%.

[0108] Furthermore, the present invention provides a lithium-ion secondary battery. The lithium-ion secondary battery includes a negative electrode, a positive electrode according to the present invention, and a separator between the negative electrode and the positive electrode. Alternatively, the lithium-ion secondary battery includes a negative electrode, a positive electrode, and a separator between the negative electrode and the positive electrode according to the present invention.

[0109] In another aspect of the present invention, an electrochemical device is provided, comprising a negative electrode, a positive electrode according to the present invention, and an electrolyte comprising lithium. Or, the electrochemical device comprises a negative electrode, a positive electrode, and an electrolyte comprising lithium according to the present invention.

[0110] The present invention also provides a solid-state battery comprising the copolymer of the present invention. [Examples]

[0111] The provided SEM images were generated using samples prepared after a solvent extraction method to remove the rubber phase. In all these images, what is observed is what remains after the rubber phase has been removed by the solvent extraction method. The steps involved in sample preparation are described below: a. A process of cutting a solid polymer sample into rectangular pieces with a length of 8-12 mm and a width of 2-3 mm using a band saw (Southbay Technologies, Model 865). b. The process of placing the polymer sample into the sample holder of the microtome device (Boeckeler Instruments). c. The sample top is cut into a square pyramid using a glass knife (Alkar, Sweden) with a distance of 3-5 mm from the apex to the base. d. Using a cryomicrotome apparatus (Boeckeler Instruments, Powertome CRX with CRX cryomicrotome unit), the sample is cryomicrotomed at -120°C using glass and diamond knives. Using a glass knife, parallel slices (1-10 micrometer slices) are prepared from the top of the sample to 0.5-0.8 mm below the top, and then using a diamond knife (Diatome, model histo-cryo), two 1-micrometer thick slices, two 250 nm thick slices, and one 100 nm thick slice are extracted. e. Remove the sample from the microtome holder, allow it to dry at room temperature until no more condensation is visible, and then immerse it in acetone at room temperature for 10 hours using a suitable glass container. f. After immersion for 10 hours, the sample is removed from the acetone solution, dried at room temperature for one hour, and then subjected to SEM analysis.

[0112] Melting Temperature: The polymer melting point was determined by differential scanning calorimetry (DSC) according to the procedure detailed in ASTM E794-06 2018. Resin samples were heated from -20°C to 210°C at a rate of 10°C / min, cooled, and reheated. The melting point was defined as the peak temperature value of the melting transition during the second heating cycle.

[0113] Heat of fusion: The heat of fusion was determined by differential scanning calorimetry (DSC) during the first heating cycle, following the procedure detailed in ASTM E793-06 2018.

[0114] Swelling: Swelling data was determined at room temperature in an electrolyte solution with EC / EMC / DEC = 3 / 5 / 2. Samples were prepared as 1 mm films by hot pressing. Weight gain data was recorded on day 7.

[0115] NMR Analysis: Copolymer composition was first determined by 19F NMR by dissolving the resin sample in a solvent mixture of triethyl phosphite and tetrahydrofuran-d8. The 19F NMR spectrum of the solution was acquired at 50°C using a Bruker AV III HD 500 MHz spectrometer (11.7 T) equipped with a 5 mm 1H / 19F / 13C TXO probe. The molar ratios of HFP and VDF were then determined from the spectrum by comparing the integrals of the CF3 and CF2 signals. The weight fractions were then calculated by multiplying the molar ratios by the molecular weights of each monomer.

[0116] Melt viscosity: Melt viscosity measured at 232°C and 100 seconds. -1 Measurement is performed according to ASTM method D3835.

[0117] [Example 1] A 2-gallon autoclave was filled with 4000 g of deionized water and 2.0 g of surfactant (Pluronic 31R1). Oxygen was removed from the autoclave contents by pressurizing with nitrogen to 60 psig, stirring at 60 rpm, and then evacuating to atmospheric pressure. This series of purging was performed three times. The reactor was then sealed, stirred, and heated to 100°C. Next, 222 g of hexafluoropropylene (HFP) was packed into the reactor. The reactor was then pressurized to 650 psig using vinylidene fluoride (VDF). A supply of 1.0 wt% potassium persulfate (KPS) and 1.0 wt% sodium acetate trihydrate (SAT) was started at 240 mL / hour. When the pressure dropped, vinylidene fluoride was supplied to the reactor at the rate necessary to maintain the pressure at 650 psig throughout the reaction. When the VDF supply was increased to 1000 mL / hour, the KPS / SAT supply was reduced to 100 mL / hour, then 50 mL / hour, then 25 mL / hour. The KPS / SAT supply rate was selected to maintain a stable supply of VDF at approximately 1000 mL / hour. When 1679 g of VDF had been supplied, the VDF supply was stopped. The KPS and SAT supply was continued at 25 mL / hour for a further 40 minutes. The reactor was cooled to 75°C and evacuated to atmospheric pressure. After evacuating, the reactor was cooled to room temperature and the product was discharged from the reactor. The product was spray-dried directly at an inlet temperature of 160°C and an outlet temperature of 90°C. The HFP content in the product is 9.1% by weight. The melting point is 138.7°C.

[0118] [Example 2] A 2-gallon autoclave was filled with 4000 g of deionized water and 2.0 g of surfactant (Pluronic 31R1). Oxygen was removed from the autoclave contents by pressurizing with nitrogen to 60 psig, stirring at 60 rpm, and then evacuating to atmospheric pressure. This continuous purging was performed three times. The reactor was then sealed, stirred, and heated to 100°C. Next, 184 g of hexafluoropropylene (HFP) was packed into the reactor. The reactor was then pressurized to 650 psig using vinylidene fluoride (VDF). A supply of 1.0 wt% potassium persulfate (KPS) and 1.0 wt% sodium acetate (SAT) was started at 240 mL / hour. As the pressure decreased, vinylidene fluoride was supplied to the reactor at the rate necessary to maintain a pressure of 650 psig throughout the reaction, and the KPS / SAT supply was reduced to 100 mL / hour, then 50 mL / hour, then 25 mL / hour. The KPS / SAT supply rate was selected to maintain a stable supply of VDF at approximately 1000 mL / hour. Once 1720 g of VDF had been supplied, the VDF supply was stopped. The KPS and SAT supply was continued at 25 mL / hour for a further 30 minutes. The reactor was cooled to 75°C and evacuated to atmospheric pressure. After evacuating, the reactor was cooled to room temperature and the product was discharged from the reactor. The product was spray-dried directly at an inlet temperature of 160°C and an outlet temperature of 90°C. The HFP content in the product is 7.3% by weight. The melting point is 140.8°C.

[0119] [Example 3] A 2-gallon autoclave was filled with 4000 g of deionized water and 2.0 g of surfactant (Pluronic 31R1). Oxygen was removed from the contents of the autoclave by pressurizing with nitrogen to 60 psig, stirring at 60 rpm, and then evacuating to atmospheric pressure. This continuous purging was performed three times. The reactor was then sealed, stirred, and heated to 100°C. Next, 146 g of hexafluoropropylene (HFP) was packed into the reactor. The reactor was then pressurized to 650 psig using vinylidene fluoride (VDF). A supply of 1.0 wt% potassium persulfate (KPS) and 1.0 wt% sodium acetate (SAT) was started at 240 mL / hour. As the pressure decreased, vinylidene fluoride was supplied to the reactor at the rate necessary to maintain the pressure at 650 psig throughout the reaction, and the KPS / SAT supply was reduced to 100 mL / hour, then 50 mL / hour, then 25 mL / hour. The KPS / SAT supply rate was selected to maintain a stable supply of VDF at approximately 1000 mL / hour. Once 1751 g of VDF had been supplied, the VDF supply was stopped. The KPS and SAT supply was continued at 30 mL / hour for a further 30 minutes. The reactor was cooled to 75°C and evacuated to atmospheric pressure. After evacuating, the reactor was cooled to room temperature and the product was discharged from the reactor. The product was spray-dried directly at an inlet temperature of 160°C and an outlet temperature of 90°C. The HFP content in the product is 5.8 wt%. The melting point is 145.0°C.

[0120] [Example 4] Example 1 was replicated, except that the amount of hexafluoropropene (HFP) was adjusted to produce a copolymer having an HFP content of 10.8% by weight.

[0121] Table 1 below shows the data obtained for the products prepared in Examples 1 to 4.

[0122] [Table 1]

[0123] The copolymers of Comparative Examples 1 and 2 were obtained by continuously adding hexafluoropropene together with vinylidene fluoride throughout the entire process. As shown in Figure 2, the copolymer of the present invention exhibits a lower melting temperature than the comparative copolymer. Therefore, the processability of the copolymer of the present invention is improved at a specified hexafluoropropene content.

[0124] The swelling at room temperature was measured for the copolymers of Example 2 and Comparative Example 2. The swelling of Example 2 was 32.7%, while the swelling of Comparative Example 2 was 49.7%. The copolymer of the present invention exhibits lower swelling than other copolymers having substantially similar melting temperatures. According to the present invention, it is possible to produce copolymers with lower melting temperatures by reducing the use of hexafluoropropene. Therefore, swelling is reduced by minimizing the hexafluoropropene content in the copolymer.

[0125] Other copolymers with higher HFP content were also prepared in Examples 5-7.

[0126] [Example 5] A 2-liter autoclave was filled with 1000 g of deionized water and 0.6 g of surfactant (Pluronic 31R1). Oxygen was removed from the autoclave contents by pressurizing with nitrogen to 60 psig, stirring at 60 rpm, and then evacuating to atmospheric pressure. This series of purging was performed three times. The reactor was then sealed and heated to 100°C with stirring at 72 rpm. Next, 90 g of hexafluoropropylene (HFP) was packed into the reactor. The reactor was then pressurized to 650 psig using vinylidene fluoride (VDF). A supply of 1.0 wt% potassium persulfate (KPS) and 1.0 wt% sodium acetate trihydrate (SAT) was started at 180 mL / hour. When the pressure dropped, vinylidene fluoride was supplied to the reactor at the rate necessary to maintain the pressure at 650 psig throughout the reaction. When a pressure drop occurred, the KPS / SAT supply was reduced to maintain a stable VDF supply of approximately 100-300 / mL. Once 360g of VDF had been supplied, the VDF supply was stopped. KPS and SAT supply was continued at 20mL / hour for another 31 minutes. The reactor was cooled to 30°C and evacuated to atmospheric pressure. After evacuating, the product was discharged from the reactor. The product was oven-dried at 60°C.

[0127] [Example 6] A 2-liter autoclave was filled with 1000 g of deionized water and 0.6 g of surfactant (Pluronic 31R1). Oxygen was removed from the autoclave contents by pressurizing with nitrogen to 60 psig, stirring at 60 rpm, and then evacuating to atmospheric pressure. This series of purging was performed three times. The reactor was then sealed and heated to 100°C with stirring at 72 rpm. Next, 134 g of hexafluoropropylene (HFP) was packed into the reactor. The reactor was then pressurized to 650 psig using vinylidene fluoride (VDF). A supply of 1.0 wt% potassium persulfate (KPS) and 1.0 wt% sodium acetate trihydrate (SAT) was started at 180 mL / hour. When the pressure dropped, vinylidene fluoride was supplied to the reactor at the rate necessary to maintain the pressure at 650 psig throughout the reaction. When a pressure drop occurred, the KPS / SAT supply was reduced to maintain a stable VDF supply of approximately 100-300 / mL. Once 315g of VDF had been supplied, the VDF supply was stopped. KPS and SAT supply was continued at 40mL / hour for another 35 minutes. The reactor was cooled to 30°C and evacuated to atmospheric pressure. After evacuating, the product was discharged from the reactor. The product was oven-dried at 60°C.

[0128] Table 2 below shows the data obtained for the products prepared in Examples 5 to 7.

[0129] [Table 2]

[0130] The present invention enables the preparation of a wide range of copolymers having improved properties.

[0131] Other copolymers according to the present invention were prepared according to the same protocol used in Example 1. The heat of fusion was determined and reported in Table 3 below.

[0132] [Table 3]

Claims

1. A copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from fluorinated monomer M1, wherein the melting temperature Tm is defined by the following relationship: (154.45-1.9472*x)-3<Tm(℃)<(154.45-1.9472*x)+3 A copolymer having (wherein x is the weight content expressed as a percentage of the fluorinated monomer M1 based on the total weight of the copolymer, and the melting temperature is measured by DSC according to the ASTM E794-06 (2018) standard test method), wherein the fluorinated monomer M1 is hexafluoropropene, and the weight content of hexafluoropropene based on the total weight of the copolymer is less than 11% by weight.

2. The copolymer according to claim 1, wherein the weight content of the fluorinated monomer M1 is 0.1% to 11% by weight based on the total weight of the copolymer, preferably 0.5% to 11% by weight based on the total weight of the copolymer, more preferably 1 to 11% by weight based on the total weight of the copolymer, more preferably 2 to 10.5% by weight based on the total weight of the copolymer, particularly 4 to 10% by weight based on the total weight of the copolymer, and more specifically 4.5 to 10% by weight.

3. The copolymer according to any one of claims 1 to 2, having a heat of fusion ΔH defined by the following relationship: (34.517 - 1.0125 * x) - 2.2 < ΔH (J / g) < (34.517 - 1.0125 * x) + 2.2; (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer, and the heat of fusion is determined by DSC according to the ASTM E793-06 (2018) standard test method.

4. Formula R １ R ２ C═C(R ３ ).C(O)R(I) (wherein, R １ , R ２ and R ３ are independently selected from the group consisting of H and C １ -C ５ alkyl, and R is -NH-C(CH ３ ). ２ CH ２ C(O)CH ３ , -NR'R" or -OR' (wherein, R' and R" are H, and one or more hydroxyl, carboxyl, thiol or amino functional groups or a 5- to 6-membered heterocyclic ring containing at least one nitrogen atom in the ring, optionally substituted C １ -C １８ alkyl groups independently selected from the group consisting of), and further comprises a repeating unit derived from a hydrophilic monomer M2 selected from the group consisting of). The copolymer according to any one of claims 1 to 3.

5. The copolymer according to any one of claims 1 to 4, further comprising repeating units derived from monomers having a functional group selected from the group consisting of carboxylic acids, carboxylic acid anhydrides, carboxylic acid esters, epoxy groups, amides, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenol, ester, ether, siloxane, sulfonic acid, sulfuric acid, phosphoric acid, or phosphonic acid.

6. The copolymer according to any one of claims 1 to 5, which is in powder form.

7. Use of the copolymer according to any one of claims 1 to 6 as a seed for preparing an interpenetrating polymer network.

8. Use of the copolymer according to any one of claims 1 to 6 in a separator for lithium-ion batteries.

9. A method for preparing copolymers, a) A step of filling the reactor with an initial packing mixture containing water, a surfactant, and fluorinated monomer M1, and adding vinylidene fluoride to the reactor until the operating pressure is reached; b) A step of initiating polymerization by adding an initiator; c) A step of forming the copolymer by continuously supplying the vinylidene fluoride and optionally the initiator until all of the vinylidene fluoride has been added to the reactor; d) The step of removing the copolymer from the reactor; e) Optionally, a step of drying the copolymer to form a powder; Includes, A method wherein the weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method is less than 11% by weight based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method, and the entire amount of the fluorinated monomer M1 used in the method is added to the reactor before step b).

10. The method according to claim 9, wherein the fluorinated monomer M1 is selected from the group consisting of hexafluoropropene, tetrafluoroethylene, chlorotrifluoroethylene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, trifluoroethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.

11. The method according to any one of claims 9 or 10, wherein the fluorinated monomer M1 is hexafluoropropene.

12. The method according to any one of claims 9 to 11, wherein the surfactant is a nonionic or nonfluorinated surfactant or a nonionic and nonfluorinated surfactant.

13. The method according to any one of claims 9 to 12, wherein the surfactant comprises polyethylene glycol segment and polypropylene glycol segment, and has an HLB value of 1 to 5 and preferably a weight-average molecular weight of 2500 to 10000 g. mol-1.

14. A hydrophilic monomer M2 is added in any one of steps a), b), and / or c), and the hydrophilic monomer M2 is of formula R １ R ２ C = C(R ３ )C(O)R(I) (wherein, R １ , R ２ and R ３ H and C １ -C ５ R is independently selected from the group consisting of alkyls, and R is -NHC(CH ３ ) ２ CH ２ C(O)CH ３ -NR'R'' or -OR' (wherein R'' and R'' are H and C, optionally substituted by one or more hydroxyl, carboxyl, thiol, or amino functional groups or a 5-6 membered heterocycle containing at least one nitrogen atom in the ring) １ -C １８ The method according to any one of claims 9 to 13, wherein the member is selected from the group consisting of (independently selected from the group consisting of alkyl groups).

15. An article formed from the copolymer according to any one of claims 1 to 6.

16. A separator for lithium-ion batteries comprising an adhesive layer on at least one side of a porous substrate, wherein the adhesive layer comprises a copolymer according to any one of claims 1 to 6 and optionally inorganic particles.

17. A positive electrode composition or a negative electrode composition comprising the copolymer according to any one of claims 1 to 6.

18. A coated substrate to which the copolymer according to any one of claims 1 to 6 is applied as an aqueous latex or solvent solution.

19. A porous membrane comprising the copolymer according to any one of claims 1 to 6, applied as an aqueous latex or solvent solution.

20. A copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from fluorinated monomer M1, wherein the melting temperature Tm is defined by the following relationship: (154.45-1.9472*x)-3<Tm(℃)<(154.45-1.9472*x)+3 A copolymer having (wherein x is the weight content of the fluorinated monomer M1 expressed as a percentage based on the total weight of the copolymer, and the melting temperature is measured by DSC according to the ASTM E794-06 (2018) standard test method), wherein the fluorinated monomer M1 is hexafluoropropene, and the weight content of hexafluoropropene based on the total weight of the copolymer is greater than 17% by weight.

21. The copolymer according to claim 20, wherein the weight content of the fluorinated monomer M1 is 17% to 50% by weight, preferably 18% to 45% by weight, and more particularly 18% to 40% by weight, based on the total weight of the copolymer.

22. A method for preparing copolymers, a) A step of filling the reactor with an initial packing mixture containing water, a nonionic and non-fluorinated surfactant, and a fluorinated monomer M1, and adding vinylidene fluoride to the reactor until the operating pressure is reached; b) A step of initiating polymerization by adding an initiator; c) A step of forming the copolymer by continuously supplying vinylidene fluoride and optionally the initiator until all of the vinylidene fluoride has been added to the reactor; d) The step of removing the copolymer from the reactor; e) Optionally, a step of drying the copolymer to form a powder; Includes, A method wherein the weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method is greater than 17% by weight based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method, the entire amount of the fluorinated monomer M1 used in the method is added to the reactor before step b), and the nonionic and nonfluorinated surfactant comprises polyethylene glycol segment and polypropylene glycol segment and has an HLB value of 1 to 5 and preferably a weight-average molecular weight of 2500 to 10000 g. mol-1.

23. The method according to claim 22, wherein the fluorinated monomer M1 is hexafluoropropene.

24. The method according to any one of claims 22 or 23, wherein the weight content of the fluorinated monomer M1 introduced into the reactor throughout the entire method is 17% to 50% by weight, preferably 18% to 45% by weight, and particularly 18% to 40% by weight, based on the total weight of vinylidene fluoride and the fluorinated monomer M1 introduced into the reactor throughout the entire method.

25. An article formed from the copolymer according to any one of claims 20 or 21.

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