Production of fluoropolymers at low temperatures

Abstract

A process is disclosed for the polymerization of vinylidene fluoride in the presence of reducing agents, particularly sulfinate, sulfonate and sulfite reducing agents of the Bruggolite® type, in combination with inorganic initiators at low reaction temperatures to obtain predominantly β-phase fluoropolymers.

Description

[Technical field]

[0001] The present invention relates to a polyvinylidene fluoride polymer having a β-phase crystallinity and a method for producing the same, and more particularly to a specific method for producing a polymer having specific properties. [Background technology]

[0002] Typically, VDF-based polymers are produced by an aqueous polymerization (typical emulsion polymerization) process in which a polymerization initiator is reacted in the presence of a fluorinated monomer and at least one surfactant (also called an emulsifier). Emulsion polymerization requires high reaction temperatures because both inorganic persulfate initiators and organic peroxide initiators require thermal decomposition. Redox initiator systems containing peroxides such as t-butyl hydrogen peroxide and metal oxidants can be used in emulsion polymerization to achieve mid-range reaction temperatures, but redox initiators usually contain a coupling agent / accelerator between the oxidizing agent and reducing agent and require a surfactant such as a fluorosurfactant.

[0003] US Patent Application Publication No. 2002 / 042353 describes sulfinic acid compounds that can be used as reducing agents.

[0004] WO 2019 / 002180 describes the use of sulfinic acid compounds as reducing agents in the presence of organic peroxides in the synthesis of fluoropolymers using fluorosurfactant-based microemulsion polymerization.

[0005] Polyvinylidene fluoride is a polymer that can crystallize into multiple phases with different chain conformations, known as the α, β, γ, and ε phases. The β phase has strong ferroelectric and piezoelectric properties due to its planar conformation and high dipole density.

[0006] PVDF has attracted much interest as a flexible piezoelectric material due to its piezoelectric properties resulting from the polar β crystalline conformation of its crystalline structure. A high percentage of β phase in PVDF can be produced by tailoring the polymer chain structure and through a second processing step. Tailoring the polymer chain structure can be achieved by copolymerization of vinylidene fluoride with selected comonomers such as vinyl fluoride (VF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE). The second processing step includes post-processing techniques such as application of temperature, pressure, cooling rate, shear forces, or addition of additives such as carbon nanotubes, ferrite particles, and clays.

[0007] Conventional techniques / methods for producing ferroelectric β-phase PVDF rely on a combination of annealing, controlled solvent evaporation, and uniaxial stretching of the sample. These methods require expensive and demanding secondary processing after the material is synthesized.

[0008] There is a desire to carry out the polymerization at even lower reaction temperatures. Persulfate polymerization initiators do not function effectively below 50° C. A lower temperature reaction is desirable because it reduces inverse units and increases melting temperature and crystallinity. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2002 / 042353 [Patent Document 2] International Publication No. 2019 / 002180 Summary of the Invention [Problem to be solved by the invention]

[0010] Surprisingly, the applicant has found that by carrying out an emulsion polymerization process comprising reacting at least one unsaturated fluorinated monomer in the presence of a redox initiation system comprising at least one inorganic peroxide and a reducing agent having a sulfinic acid group at a temperature below 70° C., preferably below 65° C., a polymer comprising a β-phase crystalline structure is obtained.

[0011] The present invention discloses a redox system that functions at low temperatures, does not use coupling agents / accelerators and surfactants, and yet provides a vinylidene fluoride based fluoropolymer that has a high melting point, high heat of fusion (first heat in DSC), and has a majority of the crystalline phase as the β phase.

[0012] According to the present invention, a high melting temperature, an inverse unit ratio of 3.2-4.2%, a high heat of fusion, and the presence of β-phase crystals formed during the polymerization process are obtained. [Means for solving the problem]

[0013] Summary of the Invention The present invention provides a method for producing a VDF-based fluoropolymer, which comprises the synthesis of a fluoropolymer comprising repeating units derived from vinylidene fluoride, comprising polymerizing vinylidene fluoride, optionally in the presence of at least one additional acrylic comonomer, in an aqueous emulsion at a temperature below 70°C, preferably in the range of 1-65°C, in the presence of a redox initiation system comprising at least one inorganic initiator and at least one reducing agent, the reducing agent comprising at least one compound having a sulfinic acid group.

[0014] The Applicant has surprisingly found that the method according to the invention allows the determination of high melting temperatures, high heats of fusion in the first cycle, and high intensity ratios using X-ray diffraction (I β(200 / 110) / [I α(020) +I γ(020) It has been found that VDF-based polymers can be produced directly from a polymerization process characterized by a β phase predominantly exceeding 10 as measured by the β-phase determination method.

[0015] In one embodiment, the present invention provides a PVDF homopolymer or a PVDF / acrylic copolymer having unexpected properties, including (A) a very high melting temperature of 170° C. or higher, preferably 172° C. to 180° C.; (B) a high heat of fusion of more than 65 J / g in the first heating step in DSC; (C) a β-phase crystalline peak intensity ratio of I β(200 / 110) / [I α(020) +I γ(020) ] is 10 or more. The β phase crystal peak intensity ratio is I β(200 / 110) / [I α(020) +I γ(020) ] is equal to.

[0016] In another embodiment, the process of the present invention comprises polymerizing vinylidene fluoride with at least one further monomer, as defined herein, in an aqueous emulsion in the presence of a reducing agent, as defined herein, and optionally additional components.

[0017] The present invention also relates to a fluorinated polymer comprising repeat units deriving from vinylidene fluoride and, optionally, from at least one additional comonomer, said polymer being advantageously obtained via the process described above.

[0018] The present invention describes a process / method for producing vinylidene fluoride based polymers at low temperatures using reducing agents, particularly sulfinate, sulfonate and sulfite reducing agents of the Bruggolite® type, in combination with inorganic initiators such as hydrogen peroxide, potassium persulfate, ammonium persulfate or sodium persulfate.

[0019] Aspects of the invention Aspect 1: 1. A polyvinylidene fluoride polymer in an aqueous emulsion comprising repeat units derived from at least 97 mole % vinylidene fluoride, optionally 0-3 mole % acrylic comonomer, said polymer having a β-phase crystalline peak intensity ratio greater than 10, preferably greater than 15, more preferably greater than 20, a heat of fusion (first heat) greater than 65 J / g, and a melting temperature of 170°C to 180°C.

[0020] Aspect 2: A method for synthesizing a fluorinated polymer comprising repeat units derived from vinylidene fluoride, comprising polymerizing vinylidene fluoride monomer, optionally in the presence of at least one acrylic comonomer, in an aqueous emulsion at a temperature range of 1°C to 65°C in the presence of a redox initiation system comprising at least one inorganic initiator and at least one reducing agent having a sulfinic group, wherein the resulting polymer has a β-phase crystalline peak intensity ratio greater than 10.

[0021] Aspect 3: The at least one reducing agent has the following formula (I): [ka] (wherein M is a hydrogen atom, an ammonium ion, a monovalent metal ion of group Ia, IIa, IIb, IVa or VIIIb of the periodic table of the elements or the equivalent of a divalent metal ion; R1 is OH, R2 is H or an alkyl, alkenyl, cycloalkyl or aryl group, which may bear one, two or three substituents independently selected from C1-C6 alkyl, OH, O-(C1-C6 alkyl), and R3 is COOM, SO3M or COOR2, where M and R2 are as defined above.) 3. The method of embodiment 2, comprising the steps of:

[0022] Aspect 4: The method of any one of claims 2 to 3, wherein the inorganic initiator is selected from the group consisting of hydrogen peroxide and inorganic persulfates (such as potassium persulfate, ammonium persulfate, and sodium persulfate); and combinations thereof.

[0023] Aspect 5: 5. The method according to any of aspects 2 to 4, wherein the inorganic initiator is used at a concentration in the range of 0.01 to 4 wt. %, based on the total VDF added to the reaction.

[0024] Aspect 6: A method according to any one of aspects 2 to 5, wherein the inorganic initiator is selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, and combinations thereof.

[0025] Aspect 7: The method according to any one of aspects 2 to 6, wherein the temperature range is 5°C to 65°C, preferably 5°C to 55°C.

[0026] Aspect 8: The method according to any one of aspects 2 to 6, wherein the temperature range is 20 to 63°C, preferably 20 to 60°C.

[0027] Aspect 9: The method of any of aspects 2-8, wherein the fluorinated polymer comprises at least 97 mol %, more preferably at least 98 mol %, and even more preferably at least 99 mol %, of repeat units derived from vinylidene fluoride, based on all repeat units of the fluorinated polymer.

[0028] Aspect 10: The method according to any one of aspects 2 to 9, wherein the fluorinated polymer is a homopolymer.

[0029] Aspect 11: Aspect 10. The method of any one of aspects 2 to 9, wherein the fluorinated polymer is a copolymer comprising repeat units derived from vinylidene fluoride and repeat units derived from at least one acrylic comonomer.

[0030] Aspect 12: The comonomer has the formula: [ka] (In the formula, R1, R2, and R3 are the same or different and each independently represents a hydrogen atom or a C1-C3 hydrocarbon group, and ROH represents hydrogen or a C1-C5 hydrocarbon moiety.) 12. The method according to any one of aspects 2 to 9 or 11, which can be represented by:

[0031] Aspect 13: 13. The method of any one of aspects 2-9 or 11-12, wherein the at least one comonomer is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; and hydroxyethylhexyl (meth)acrylate.

[0032] Aspect 14: 14. The method according to any one of aspects 2 to 13, wherein the polymer has a β-phase crystalline peak intensity ratio of greater than 15, preferably greater than 20.

[0033] Aspect 15: The method according to any one of aspects 2 to 14, wherein the fluorinated polymer has a melting point of 170 to 180°C.

[0034] Aspect 16: 16. The method of any of aspects 2-15, wherein the fluoropolymer has a heat of fusion (1st heat) greater than 65 J / g, preferably greater than 70 J / g.

[0035] Aspect 17: The fluorinated polymer is 19 17. The method of any of aspects 2-16, having an inverse unit ratio of 3.2 to 4.2% as measured by F-NMR.

[0036] Aspect 18: The reducing agent has the following formula (II): [ka] (wherein M is a hydrogen atom, an ammonium ion, a monovalent metal ion; R1 is -OH, R2 is a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, a 5- or 6-membered cycloalkyl group, or a 5- or 6-membered aryl group; R3 is -COOM, -SO3M, or -COOR2, where M and R2 are as defined above), and a salt thereof with at least one monovalent metal ion, preferably M is a hydrogen atom or a monovalent metal ion, preferably the monovalent metal ion is selected from sodium and potassium, and preferably R2 is selected from a hydrogen atom, a linear alkyl group having 1 to 3 carbon atoms, a branched alkyl group having 1 to 3 carbon atoms, or a 5- or 6-membered aryl group.

[0037] Aspect 19: 2. The polyvinylidene fluoride polymer of embodiment 1, wherein the polymer has a β-phase crystalline peak intensity ratio greater than 30.

[0038] Aspect 20: A polymer produced by the method according to any one of aspects 2 to 18.

[0039] Aspect 21: A use of a polymer produced by the method according to any one of aspects 2 to 18 in a battery. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 shows the wide-angle X-ray diffraction of the PVDF produced by the present invention (for the β phase). (The β phase shows a clear peak at 2θ=20.26° for the sum of the diffraction from the (110) and (200) planes.) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Detailed Description of the Invention Unless otherwise specified, all percentages, parts, ratios, etc. are by weight.

[0042] The present invention provides a suitable method for producing fluoropolymers from fluoromonomers. The fluoropolymers are produced in an aqueous polymerization reaction mixture containing an inorganic initiator, preferably a persulfate, and one or more sulfinic acid derivative reducing agents. Optionally, the polymerization to produce the fluoropolymers can be carried out in the presence of a chain transfer agent to obtain regular molecular weight, a buffer to maintain a desired pH range during polymerization, and an antifouling agent to reduce or eliminate adhesion of the polymer to the inner surfaces of the polymerization vessel. The present invention also provides a method for producing fluoropolymers with unique properties, including, but not limited to, high melting points, high heats of fusion (first heating cycle), and predominantly β-phase crystal structure.

[0043] Fluoropolymers refer to homopolymers and copolymers having functional acrylic comonomers containing less than 3 mol %, preferably less than 2 mol %, more preferably less than 1 mol % of acrylic comonomer units based on the total monomer units in the polymer. Generally, the amount of acrylic comonomer is 0.01 wt % or more. The copolymers formed may be homogeneous or heterogeneous and may have a controlled structure such as star copolymers, branched random copolymers or block copolymers.

[0044] The vinylidene fluoride polymers of the present invention are conveniently prepared by aqueous polymerization, preferably emulsion polymerization, using a redox initiation system. The polymerization process can be a batch, semi-batch or continuous polymerization process.

[0045] The polymerization process preferably does not contain any fluorine-containing compounds or molecules other than the monomers and the resulting polymerization products. No fluorosurfactants are used.

[0046] The following general procedure can be followed: the reactor is first charged with deionized water free of dispersants, optionally chain transfer agents, antifouling agents and buffers, and then deoxygenated (removed of oxygen). After the reactor reaches the desired temperature, vinylidene fluoride and optionally acrylic comonomer are added to the reactor to reach a predetermined pressure. Once the desired reaction pressure is reached, oxidizing and reducing agents are added to initiate and maintain the reaction. After the desired solids level is reached, the monomer feed can be stopped, although the initiator feed can be stopped or continued to consume unreacted monomer. After the initiator charge is stopped, the reactor can be cooled and agitation can be stopped. The unreacted monomer can be vented and the copolymer produced can be recovered by a drain port or other recovery means.

[0047] The reactor used for the polymerization is a pressurized polymerization reactor. The reactor is usually equipped with an agitator and heat control means. The agitation may be constant or may be varied during the course of the polymerization to optimize the process conditions. The process according to the invention can be preferably carried out continuously or in semi-batch or batch mode.

[0048] The polymerization temperature is typically 1° C. to 65° C., preferably 5° C. to 65° C., or 20° C. to 60° C., or 5° C. to 55° C. The temperature can be changed during the reaction, preferably the temperature is kept constant at ±0.5° C. The polymerization temperature is typically higher than 1° C., higher than 5° C., or higher than 20° C., and typically lower than 65° C., lower than 60° C., or lower than 55° C.

[0049] The polymerization pressure can vary from 1380 to 12500 kPa depending on the reactor capacity, the initiator system selected, and the monomer selection. The polymerization pressure is preferably from 2000 to 9000 kPa, and most preferably from 3500 to 5500 kPa.

[0050] In general, the reaction time is preferably not more than 150 minutes, preferably not more than 120 minutes, more preferably not more than 100 minutes. In general, the reaction time is preferably at least 30 minutes.

[0051] Advantageously, the method of the present invention comprises polymerizing vinylidene fluoride in the presence of a redox initiation system comprising at least one inorganic initiator (oxidizing agent) and at least one compound having at least one sulfinic acid group (reducing agent) and at least one composition comprising, optionally, additional components.

[0052] Oxidizing agent The reaction is initiated and maintained by the addition of an inorganic radical initiator, in particular an inorganic peroxide. Preferably, inorganic persulfates are used as initiators in the present invention.

[0053] Organic peroxides are not used in the present invention. Organic peroxides require the presence of a surfactant, preferably a fluorosurfactant, and a catalyst to obtain good reaction rates.

[0054] Preferably, the inorganic radical initiator is selected from the group consisting of hydrogen peroxide, persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, preferably potassium persulfate in combination with sodium acetate or sodium acetate trihydrate.

[0055] Typical inorganic persulfates (sodium, potassium or ammonium persulfate) have useful activity within the temperature range of 65° C. to 105° C. However, "redox" systems can function at lower temperatures, for example, combinations of oxidizing agents such as hydrogen peroxide or inorganic persulfates with reducing agents such as sulfinate, sulfonate and / or sulfite reducing agents (such as Bruggolite® type reducing agents).

[0056] The total amount of inorganic initiator used is 0.01% to 4.0% by weight, more preferably 0.1% to 3% by weight, based on the total weight of the monomers used. A mixture of one or more inorganic initiators as defined above can be used to carry out the polymerization at a desired rate. Typically, sufficient initiator is added initially to start the reaction, and then additional initiator can be optionally added to maintain the polymerization at a convenient or desired rate.

[0057] Reducing Agent The reducing agent comprises at least one compound having at least one sulfinic acid group ("sulfinic acid compound"). A description of such reducing agents can be found in U.S. Patent Application Publication No. 2002 / 0042353, which is incorporated herein by reference.

[0058] The reducing agent is a composition comprising at least Formula I, optionally Formula II, and optionally Formula III. The reducing agent composition comprises at least 30% by weight of Formula I.

[0059] The reducing agent is non-fluorinated.

[0060] Formula I is represented by the following formula: [ka]

[0061] In formula I, M is a hydrogen atom, an ammonium ion, a monovalent metal ion of group Ia, IIa, IIb, IVa or VIIIb of the periodic table of the elements or the equivalent of a divalent metal ion; R1 is H, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group, which may carry one, two or three substituents independently selected from C1-C6-alkyl, OH, O-C1-C6-alkyl; R2 is COOM, SO3M or COOR5, where M is as defined above and R5 is H or a linear or branched alkyl chain having 1 to 6 carbons.

[0062] Formula II: [ka] In formula II, M is a hydrogen atom, an ammonium ion, a monovalent metal ion, R1 is a hydrogen atom, a linear alkyl group having 1-6 carbon atoms, a branched alkyl group having 1-6 carbon atoms, a 5- or 6-membered cycloalkyl group, or a 5- or 6-membered aryl group, R2 is -COOM, -SO3M, or -COOR5, where R5 is H, or a linear or branched alkyl chain having 1-6 carbon atoms, M is as defined above, and a salt thereof with at least one monovalent metal ion. Preferably, M is a hydrogen atom or a monovalent metal ion. Preferably, the monovalent metal ion is selected from sodium and potassium. Preferably, R2 is selected from a hydrogen atom, a linear alkyl group having 1-3 carbon atoms, a branched alkyl group having 1-3 carbon atoms, and a 5- or 6-membered aryl group. Preferably, R3 is selected from -COOM, -SO3M, and COOR5.

[0063] Formula III: [ka] In formula III, M is a hydrogen atom, an ammonium ion, or a monovalent metal ion, preferably Na2SO3.

[0064] Suitable examples of said reducing agents are commercially available under the trade name Bruggolite® from the BRUGGEMANN-GROUP company.

[0065] The reducing agent is used in an amount of 0.01% to 4.0% by weight, more preferably 0.1% to 3% by weight, based on the total weight of the monomers used.

[0066] Surfactants The process of the present invention is carried out in the absence of surfactants.

[0067] Chain Transfer Agents Chain transfer agents can be added to the polymerization to control the molecular weight of the product. The chain transfer agent may be added all at once at the start of the polymerization or may be added stepwise or continuously throughout the reaction. The amount and manner of addition of the chain transfer agent depends on the activity of the particular chain transfer agent employed and the desired molecular weight of the polymer product. The amount of chain transfer agent added to the polymerization reaction is about 0 to 5 weight percent, preferably 0.05 to about 5 weight percent, more preferably about 0.1 to about 2 weight percent, based on the total weight of the monomers added to the reaction mixture. Examples of chain transfer agents useful in the present invention include oxygenated compounds such as alcohols (preferably those having 3 to 10 carbons), carbonates, ketones, esters and ethers, including acetone, ethyl acetate, diethyl ether, methyl-t-butyl ether, isopropyl alcohol, and the like, which can also function as chain transfer agents, bis(alkyl)carbonates, such as bis(ethyl)carbonate, bis(isobutyl)carbonate, where the alkyl has 1 to 5 carbon atoms; ethane, propane, and the like, but are not limited thereto.

[0068] Although not preferred, paraffin-based antifoulants can be used if desired, as can long chain saturated hydrocarbon waxes or oils. The reactor loading of paraffin can be 0.01% to 0.3% by weight based on the total weight of monomers used.

[0069] Monomer The major monomer used in the present invention (meaning greater than 97% by weight of the polymer) is vinylidene fluoride. Other ethylenically unsaturated monomers may be present. The term "fluoropolymer" refers to a polymer formed by polymerization of vinylidene fluoride and, optionally, (meth)acrylic comonomers, and includes homopolymers, copolymers, terpolymers, and higher order polymers that are thermoplastic in nature and can be formed into a useful part by applying heat to cause it to flow, such as occurs in molding and extrusion processes. Fluoroplastics contain at least 97% by weight of vinylidene fluoride. Thermoplastic polymers exhibit a crystalline melting point.

[0070] The optional (meth)acrylic comonomer can be represented by the formula: [ka] In the formula, R1, R2, and R3 are the same or different and each independently represents a hydrogen atom or a C1-C3 hydrocarbon group, and ROH represents a hydrogen atom or a C1-C5 hydrocarbon moiety. Non-limiting examples of (meth)acrylic monomers include acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; hydroxyethylhexyl (meth)acrylate; acrylic acid esters such as alkyl (meth)acrylates; and vinyl esters such as vinyl acetate, vinyl propionate, and vinyl butyrate. Preferably, R1, R2, and R3 are hydrogen.

[0071] Buffer The polymerization reaction mixture may optionally contain a buffer to maintain a controlled pH throughout the polymerization reaction. The pH is preferably controlled within the range of about 4 to about 8 to minimize undesirable color development in the product.

[0072] The buffer has at least one pK in the range of about 4 to about 10, preferably about 4.5 to about 9.5. a value and / or pK b The buffer may include an organic or inorganic acid or an alkali metal salt thereof having a value of 0.1 to 100%, or a base or salt of such an organic or inorganic acid. Preferred buffers in the practice of the invention include, for example, phosphate buffers and acetate buffers. A "phosphate buffer" is one or more salts of phosphoric acid. An "acetate buffer" is a salt of acetic acid.

[0073] The dispersion resulting from the polymerization of the present invention has a solids level of 10-50% by weight, preferably 15-40% by weight. The fluoropolymer particles in the dispersion have a primary particle size in the range of 50-600 nm, preferably 100-500 nm.

[0074] The polymer or copolymer can be isolated using standard techniques such as oven drying, spray drying, shear coagulation or acid coagulation followed by drying.

[0075] In a further aspect, the present invention relates to an article made from a composition comprising at least a polymer as defined above.

[0076] In a further aspect, the present invention relates to a method for producing a shaped article, said method comprising processing a composition comprising at least a polymer as defined above.

[0077] The polymers can be processed into shaped articles of the desired shape, for example by molding (injection molding, extrusion), calendaring or extrusion. If necessary, the articles are subjected to vulcanization (or curing) during processing and / or in a subsequent step (post-treatment or post-curing).

[0078] Polymer properties The resulting polymer is thermoplastic.

[0079] A novel polymerization process results in a novel polymer composition, which comprises a PVDF copolymer, the PVDF polymer being melt processable.

[0080] The polymer is preferably not crosslinked.

[0081] The PVDF polymer contains at least 97% by weight VDF, preferably at least 98% by weight VDF. The PVDF polymer contains up to 100% by weight VDF.

[0082] The PVDF homopolymer and PVDF copolymer of the present invention are characterized by having a melting temperature of 170° C. to 180° C., preferably 171° C. to 178° C. (ASTM D3418), as measured by DSC.

[0083] The polymer of the present invention is 19 It has an inverse unit ratio of 3.2-4.2% as measured by F-NMR.

[0084] The polymers of the present invention have a heat of fusion measured by DSC (ASTM D3418) of greater than 65 J / g, preferably greater than 70 J / g, during the heating process.

[0085] The polymers produced according to the invention contain a measurable level of crystalline polyvinylidene fluoride, as can be shown by the presence of a crystalline melting point in a Differential Scanning Calorimetry (DSC) experiment. The melting temperature is assigned to the endothermic peak in the second cycle. The heat of fusion is determined in the first cycle. The DSC scans to measure the crystalline content are performed according to ASTM standard D3418. The DSC is performed in a three-stage cycle. The cycle starts at -20°C, then heats up to 210°C at 10°C / min, holds for 10 minutes, then cools the sample to -20°C at 10°C / min, then reheats to 210°C at 10°C / min.

[0086] The present invention provides a polymer having predominantly β-phase crystallinity. β(200 / 110) / [I α(020) +I γ(020) The β-phase crystalline peak intensity ratio, defined as the ratio of the β-phase crystalline peak intensity to the β-phase crystalline peak intensity, of the polymer of the present invention is preferably greater than 15, or greater than 20, or greater than 30, or greater than 40, or greater than 45, as measured using X-ray diffraction as described in the Examples.

[0087] The present invention provides a β-phase rich polyvinylidene fluoride that is superior to conventional techniques such as copolymerization and secondary processing methods.

[0088] The melt viscosity of the polymer of the present invention is generally in the range of 5 to 75, preferably 35 to 75 kpoise, and more preferably 35 to 65 kpoise (ASTM D3835, 232°C, 100 seconds -1 ).

[0089] The polymers of the present invention are applicable to the manufacture of high performance, low cost actuator applications. EXAMPLES

[0090] Examples 1-4 The experiment was carried out by adding 1000 g of water to a 1.7 L stainless steel reactor. The reactor was purged with nitrogen gas. The reactor was sealed and stirring was started at 72 RPM. Stirring at 72 RPM was maintained throughout the reaction. The reactor was heated to the desired temperature. The reactor was charged with vinylidene fluoride to reach the desired pressure of 4500 kPa. After pressurization, the reactor was charged with initiator and reducing agent solutions. The initiator solution was 1% potassium persulfate in aqueous initiator solution (EMD Chemicals, ACS grade). The reducing agent solution was 1% FF6M (Bruggolite) solution. The aqueous initiator and reducing agent solutions were added continuously to the reaction to obtain an adequate polymerization rate. The reaction temperature was maintained and the reaction pressure was maintained at 4500 kPa by adding vinylidene fluoride as needed. When the VDF consumption reached the desired level, the VDF feed was stopped. Stirring was continued and temperature was maintained for 30 minutes. Stirring and heating were then discontinued. After cooling to room temperature, excess gas was vented and the latex produced by the reaction was discharged into a suitable receiving vessel. Gravimetric solids determinations of the latex were made. The latex was coagulated by conventional means, including freezing, or dried directly in a convection oven at 110°C.

[0091] The particle size of the dispersion was measured using a Nicomp Model 380 Sub-Micron Particle Sizer containing a single mode 35 mW laser diode with a wavelength of 639 nm.

[0092] The melt viscosity of the resin was measured by capillary rheometry using a DYNISCO LCR-7000 at 232°C for 100 seconds in accordance with ASTM D3835.

[0093] Thermal properties were measured according to ASTM standard D3418 using a TA Instruments DSC Q2000 with LNCS from -20°C to 210°C at 10°C / min cycles.

[0094] Solids content was determined gravimetrically.

[0095] The inverse units were determined using NMR. 19 F-NMR spectra were recorded on a Bruker AVIII HD500 spectrometer using DMSO-d6 as the solvent. The intensity of the peaks (integral values) in the range of 91–92 ppm was assigned to the fluorine atoms present in the isoregic unit, and the intensity of the peaks in the range of 112–116 ppm was assigned to the fluorine atoms present in the inverse unit.

[0096] X-ray diffraction experiments were performed on a Rigaku SmartLab diffraction platform (Cu Kα 1.5418 Å, 40 kV, 40 mA). The samples were placed in a low background holder and WAXS analysis was performed in reflection mode. The diffractometer used for WAXS analysis is a Rigaku SmartLab equipped with a copper X-ray tube (Cu Kα 1.5418 Å) and set at 40 kV, 40 mA with a line focus (X-ray beam is used in a line focus with a length of 12 mm and a width of 1 mm). The experiments are performed in θ-θ (reflection) geometry with parallel beam optics (curved parabolic multilayer mirror, which turns the naturally diverging X-ray beam into a parallel X-ray beam with very low divergence). The entrance slit is set to 1 mm aperture, the length limiting slit to 10 mm aperture, and the two receiving slits to 3 mm aperture. The detector is a Rigaku Hi-Pix 3000 used in 1D mode. Data were collected in continuous mode from 5.0° to 80.0° 2θ with a step of 0.02° and a scan rate of 0.5° / min. The ratio of β-PVDF to α-PVDF and / or γ-PVDF was calculated as the intensity ratio: the sum of β-PVDF(200) and β-PVDF(110) divided by the sum of α-PVDF(020) and γ-PVDF(020).

[0097] The control is a PVDF homopolymer prepared by conventional emulsion polymerization at temperatures above 75°C using persulfate as the initiator.

[0098] Table 1: Homopolymer - No Surfactant JPEG2024538309000009.jpg57127

[0099] Table 2: JPEG2024538309000010.jpg66150

[0100] (1) Peak intensity ratio calculated using the ratio of the sum of the β(200) and β(110) peaks observed with Cu Kα radiation near 20.6° 2θ to the sum of the α(020) peak intensity observed with Cu Kα radiation near 18.3° 2θ, or the γ(020) peak intensity observed with Cu Kα radiation near 18.3° 2θ, or the sum of the α(020) and γ(020) peak intensities when both polymorphs were present.

[0101] Experiments 1-4 show that the polymerization method of the present invention results in β-phase as evidenced by the intensity ratio and high ΔH. In a typical emulsion (control), β-phase is not present. The novel polymerization method results in fewer inverse units while obtaining a higher melting temperature compared to the control.

[0102] Runs 5-6: Runs were run by adding 6000 g of water to a 2 gallon stainless steel reactor. The reactor was purged with nitrogen gas. The reactor was sealed and agitation was started at 72 RPM. Agitation at 72 RPM was maintained throughout the reaction. The reactor was heated to the desired temperature. The reactor was charged with vinylidene fluoride and allowed to reach the desired pressure of 650 psi. After pressurization, the reactor was charged with initiator and reducing agent solutions. The initiator solution was a 1% aqueous potassium persulfate initiator solution (EMD Chemicals, ACS grade). The reducing agent solution was a 1% FF6M (Bruggolite) solution. The aqueous initiator and reducing agent solutions were added to the reaction as a slug or continuous feed to obtain adequate polymerization rates. The comonomer solution was fed to the reactor immediately after the initiator solution and continued to be fed to the reactor throughout the reaction. The reaction temperature was maintained and the reaction pressure was maintained at 650 psi by adding vinylidene fluoride as needed. When the VDF consumption reached the desired level, the VDF feed was stopped. Agitation was continued and temperature was maintained for 30 minutes. Agitation and heating were then discontinued. After cooling to room temperature, excess gas was vented and the latex produced by the reaction was discharged into a suitable receiving vessel. Gravimetric solids determinations of the latex were made. The latex was coagulated by conventional means, including freezing, or directly dried in a convection oven at 110°C.

[0103] JPEG2024538309000011.jpg41154

[0104] JPEG2024538309000012.jpg34141

[0105] Runs 5 and 6 showed similar results to runs 1-4, i.e., β-phase, higher melting points, and higher ΔH compared to the control.

[0106] Examples 7 to 8 (VDF-based fluorinated copolymer - Comparative examples) The experiment was carried out by adding 1000 g of water to a 1.7 L stainless steel reactor. The reactor was purged with nitrogen gas. The reactor was sealed and stirring was started at 72 RPM. The stirring at 72 RPM was maintained throughout the reaction. The reactor was heated to the desired temperature. The reactor was charged with vinylidene fluoride and comonomer to reach the desired pressure of 4481 kPa (650 psi). After pressurization, the reactor was charged with an initiator solution and a reducing agent solution. The initiator solution was a 1% aqueous solution of potassium persulfate (EMD Chemicals, ACS grade). The reducing agent solution was a 1% aqueous solution of FF6M (Bruggolite). The aqueous initiator solution and the reducing agent solution were continuously fed and added to the reaction to obtain an adequate polymerization rate. The reaction pressure was maintained at 4481 kPa (650 psi) by holding the reaction temperature and adding vinylidene fluoride and comonomer as needed. When the VDF consumption reached the desired level, the VDF feed was stopped. Stirring was continued and the temperature was maintained for 30 minutes. Stirring and heating were then discontinued. After cooling to room temperature, the excess gas was vented and the latex produced by the reaction was discharged into a suitable receiving vessel. Gravimetric solids determinations of the latex were made. The latex was coagulated by conventional means, including freezing, or directly dried in a convection oven at 110°C.

[0107] JPEG2024538309000013.jpg78149

[0108] JPEG2024538309000014.jpg32136

[0109] The melting temperature of Comparative Example 7 was 163° C. No β-phase crystals were observed. The melting temperature of Comparative Example 8 was 125° C. No β-phase crystals were observed.

Claims

1. 1. A polyvinylidene fluoride polymer in an aqueous emulsion comprising repeat units derived from at least 97 mole % vinylidene fluoride and optionally 0-3 mole % acrylic comonomer, said polymer having a β-phase crystalline peak intensity ratio greater than 10, preferably greater than 15, a heat of fusion greater than 65 J / g during the first heating process in DSC, and a melting temperature of 170°C to 180°C.

2. A method for synthesizing a fluorinated polymer comprising repeating units derived from vinylidene fluoride, comprising polymerizing vinylidene fluoride monomer, optionally in the presence of at least one acrylic comonomer, in an aqueous emulsion at a temperature ranging from 1°C to 65°C in the presence of a redox initiation system comprising at least one inorganic initiator and at least one reducing agent having a sulfinic group, wherein the resulting polymer has a β-phase crystalline peak intensity ratio of greater than 10.

3. The at least one reducing agent is a compound of the following formula (I): 【Chemical 1】 wherein M is a hydrogen atom, an ammonium ion, a monovalent metal ion of Group Ia, IIa, IIb, IVa, or VIIIb of the Periodic Table of the Elements, or the equivalent of a divalent metal ion; R 1 is OH, and R 2 is H or an alkyl, alkenyl, cycloalkyl or aryl group, and these groups are 1 ~C 6 Alkyl, OH, O-(C 1 ~C 6 alkyl), and R 3 COOM, SO 3 M or COOR 2 where M and R 2 is as defined above.) 3. The method of claim 2, comprising:

4. 4. The method of claim 3, wherein the inorganic initiator is selected from the group consisting of hydrogen peroxide, inorganic persulfates, and combinations thereof.

5. 3. The process of claim 2, wherein the inorganic initiator is used at a concentration ranging from 0.01 to 4% by weight, based on the total VDF added to the reaction.

6. 3. The method of claim 2, wherein the inorganic initiator is selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, and combinations thereof.

7. 3. The method of claim 2, wherein the temperature range is from 5°C to 60°C.

8. 5. The method of claim 4, wherein the temperature range is 20 to 60°C.

9. 5. The method of claim 4, wherein the fluorinated polymer comprises at least 97 mole percent repeat units derived from vinylidene fluoride, based on the total repeat units of the fluorinated polymer.

10. The method of claim 9 wherein the fluorinated polymer is a homopolymer.

11. 10. The method of claim 9, wherein the fluorinated polymer is a copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from at least one acrylic comonomer.

12. The comonomer has the formula: 【Chemistry 2】 (In the formula, R1, R2, and R3 are the same or different, and each independently represents a hydrogen atom or C 1 ~C 3 is a hydrocarbon group, and ROH is hydrogen or C 1 ~C 5 It is a hydrocarbon portion.) The method of claim 11, which can be expressed as:

13. 12. The method of claim 11, wherein the at least one comonomer is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; and hydroxyethylhexyl (meth)acrylate.

14. 3. The method of claim 2, wherein the polymer has a β-phase crystalline peak intensity ratio of greater than 15.

15. The method of claim 2, wherein the fluorinated polymer has a melting point of 170 to 180°C.

16. 3. The method of claim 2, wherein the fluoropolymer has a heat of fusion greater than 65 J / g during the first heating process in a DSC.

17. The fluorinated polymer 19 3. The method of claim 2, having an inverse unit ratio of 3.2 to 4.2% as measured by F-NMR.

18. The reducing agent has the following formula (II): 【Chemistry 3】 (wherein M is a hydrogen atom, an ammonium ion, or a monovalent metal ion; R 1 is —OH, and R 2 is a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, a 5- or 6-membered cycloalkyl group, or a 5- or 6-membered aryl group; R 3 is -COOM, -SO 3 M, or -COOR 2 where M and R 2 is as defined above.) and salts thereof with at least one monovalent metal ion.

19. 10. The polyvinylidene fluoride polymer of claim 1, wherein the polymer has a β-phase crystalline peak intensity ratio greater than 30.

20. A polymer produced by the method according to any one of claims 2 to 18.

21. 3. Use of a polymer produced by the method of claim 2 in a battery.

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