Polymerization of vinylidene fluoride in water using polymeric suspending agents

Abstract

FIELD OF THE INVENTION The present invention relates to vinylidene fluoride polymers, methods for making vinylidene fluoride polymers, and articles comprising vinylidene fluoride polymers.

Description

[Technical Field]

[0001] This application claims priority from European Patent Application No. 20197702.2, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to vinylidene fluoride polymers, methods for making said vinylidene fluoride polymers, and articles comprising said vinylidene fluoride polymers. [Background technology]

[0003] Vinylidene fluoride polymers are used advantageously in several different applications.

[0004] Poly(vinylidene fluoride) (PVDF) can be obtained by polymerization of vinylidene difluoride monomer (difluoro 1,1-ethylene, VF2 or VDF) by either suspension or emulsion polymerization.

[0005] The main advantage of suspension polymerization of VDF compared to emulsion polymerization is that it is possible to carry out the process in the absence of surfactants, in particular in the absence of fluorinated surfactants.

[0006] However, during the suspension polymerization of VDF in the absence of any suspending agent, reactor fouling (which is the accumulation of polymer deposits on the inner surfaces of the reactor and stirring equipment) has been observed, which prevents the process from being scaled up to industrial production.

[0007] The use of non-ionic suspending agents in VDF suspension polymerization is known in the art. For example, WO 2016 / 041808 discloses the reduction of fouling in VDF polymerization by using a mixture of non-ionic surfactants containing an alkylene oxide polymer (PAO) and a non-ionic hydroxyalkyl cellulose.

[0008] However, the non-ionic suspending agent may not be effectively removed during the polymer purification step, which is a necessary step to obtain a good quality VDF polymer suitable for use in some applications.

[0009] The purification step includes washing the polymer particles with pure water, so that the higher the solubility of the suspending agent in water, the higher the purification efficiency, and thus the higher the purity of the PVDF polymer.

[0010] Among suspending agents, ionic ones have the highest water solubility. However, the use of ionic suspending agents in the suspension polymerization of VDF can lead to unstable reactions, and the reaction control may not be sufficient to safely scale up production to industrial levels.

[0011] Therefore, there remains a need in the art for a process for producing vinylidene fluoride polymers that results in purer, industrially feasible PVDF. Summary of the Invention

[0012] It has now surprisingly been found that the process of the present invention makes it possible to avoid reactor fouling and at the same time advantageously facilitate the production of vinylidene fluoride polymers by using a specific blend of suspending agents which are easily washed away from the polymer at the end of the polymerization.

[0013] In a first aspect, the present invention relates to a method for producing vinylidene fluoride polymers [polymer (VDF)] in aqueous suspension, said method comprising: A) at least a non-ionic suspending agent; and B) at least an ionic carboxyalkyl cellulose The polymerisation step comprises polymerising in the presence of

[0014] The present inventors have surprisingly found that by using a mixture of at least an ionic suspending agent and at least a non-ionic suspending agent, the amount of non-ionic suspending agent can be greatly reduced while still achieving controllable polymerization without fouling.

[0015] Therefore, in a second aspect, the present invention relates to a vinylidene fluoride polymer [polymer (VDF)] obtainable by the process of the invention.

[0016] It has also surprisingly been found that the vinylidene fluoride polymer powder obtained by the process of the present invention is characterized by bead-like, substantially round particles having a particle size distribution with a D50 value of greater than 150 microns, and advantageously exhibits excellent flowability.

[0017] In a third aspect, the present invention relates to a composition [composition (C)] containing at least one polymer (VDF) according to the invention.

[0018] In a fourth aspect, the present invention relates to an article comprising the composition (C) of the present invention. [Brief explanation of the drawings]

[0019] [Figure 1] 1 shows SEM images of the polymer (VDF) or the powder of Example 1 at 50x magnification. [Figure 2] 1 shows an SEM image of particles of PVDF polymer produced according to standard processes in pellet form and then milled to reduce particle size, at a magnification of 2.55Kx. DETAILED DESCRIPTION OF THE INVENTION

[0020] Unless otherwise stated, in the context of the present invention, all percentages relate to the ratio of the weight of a particular component of the mixture divided by the total weight of the mixture (expressed as wt / wt).

[0021] As used herein, the term "substantially round" and related morphologies refer to particles that have a substantially round appearance in both cross-sectional planes and do not have an elongated body.

[0022] As used herein, the term "vinylidene fluoride polymer" refers to a polymer that contains more than 50 mole percent, preferably more than 80 mole percent, of repeat units derived from the polymerization of vinylidene fluoride monomers (difluoro 1,1-ethylene, VF2 or VDF).

[0023] For the purposes of the present invention, vinylidene fluoride polymers are preferably homopolymers containing repeat units derived exclusively from VDF.

[0024] For the purposes of the present invention, vinylidene fluoride polymers may optionally contain, in addition to VDF monomers, repeating units different from VDF repeating units and resulting from the polymerization of ethylenically unsaturated monomers different from VDF (e.g., 0.1 to 20 mol %, preferably 0.5 to 10 mol %, based on the total number of moles of the composition). The ethylenically unsaturated monomers may contain at least one fluorine atom and therefore may be designated as fluorinated comonomers. Nevertheless, the ethylenically unsaturated monomers may not contain fluorine atoms; examples of these non-fluorinated comonomers are, in particular, hydrophilic (meth)acrylic monomers.

[0025] The hydrophilic (meth)acrylic monomer (MA) preferably has the formula: [ka] (wherein R1, R2, and R3 are equal to or different from each other and independently represent a hydrogen atom or a C1-C3 hydrocarbon group, and R OH is hydrogen or a C1-C5 hydrocarbon moiety containing at least one hydroxyl group. Non-limiting examples of hydrophilic (meth)acrylic monomers (MA) are, inter alia, acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; hydroxyethylhexyl (meth)acrylate.

[0026] The monomer (MA) is more preferably - Hydroxyethyl acrylate (HEA) of the formula: [ka] - 2-hydroxypropyl acrylate (HPA) of any of the following formulas: [ka] - Acrylic acid (AA) of the formula: [ka] - and mixtures thereof.

[0027] Most preferably, the monomer (MA) is AA and / or HEA.

[0028] Non-limiting examples of fluorinated comonomers different from VDF as detailed above are in particular: (i) C2-C8 fluoroolefins, such as trifluoroethylene (TrFE), tetrafluoroethylene (TFE) and hexafluoropropylene (HFP); (ii) Formula CH2=CH-R f0 (In the formula, R f0 is a C2-C6 perfluoroalkyl group); (iii) chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins, such as chlorotrifluoroethylene (CTFE); (iv) Formula CF2=CFOR f1 (In the formula, R f1 is a C1-C6 perfluoroalkyl group), such as perfluoromethyl vinyl ether (PMVE) and perfluoropropyl vinyl ether (PPVE); (v) Formula CF2 = CFOX0 (wherein X0 is C1 to C 12C1-C having an oxyalkyl group or one or more ether groups 12 (per)fluorooxyalkyl vinyl ethers of (per)fluorooxyalkyl groups, such as perfluoro-2-propoxypropyl groups; (vi) Formula CF2 = CFOCF2OR f2 (In the formula, R f2 is a C1-C6 (per)fluoroalkyl group, such as -CF3, -C2F5, -C3F7, or a C1-C6 (per)fluorooxyalkyl group having one or more ether groups, such as -C2F5-O-CF3; (vii) Formula CF2 = CFOY0 (wherein Y0 is C1 to C 12 Alkyl group or (per)fluoroalkyl group, C1-C 12 C1-C with oxyalkyl group and one or more ether groups 12 (per)fluorooxyalkyl groups, where Y0 contains a carboxylic or sulfonic acid group in its acid, acid halide or salt form); (viii) fluorodioxoles, in particular perfluorodioxoles; (ix) vinyl fluoride, and A mixture of them Includes:

[0029] The most preferred fluorinated comonomers are chlorotrifluoroethylene (CTFE), trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PMVE).

[0030] In one embodiment of the present invention, the polymer (VDF) is preferably - repeating units derived from vinylidene fluoride; - 0.1 mol % to 3 mol % of repeating units derived from at least one (meth)acrylic monomer [monomer (MA)], relative to the total molar amount of repeating units of said polymer (VDF); - 0.1 mol % to 10 mol %, preferably 0.2 mol % to 5 mol % of repeating units derived from vinylidene fluoride (VDF) relative to the total molar amount of repeating units of the polymer (VDF); and more preferably consists of these.

[0031] The process of the present invention is a polymerization carried out in aqueous suspension.

[0032] For the purposes of this invention, polymerization in aqueous suspension refers to a process in which the reaction medium is formed from an organic phase and water is added to help disperse the heat generated during the reaction. The organic phase can be formed by the monomers themselves, without the addition of a solvent, or by dissolving the monomers in a suitable organic solvent in the presence of a suitable organic initiator and a water-soluble suspending agent having repeating molecular units in its structure.

[0033] The polymerization reaction can be carried out under conditions of temperature and pressure such that the more abundant monomer, ie, VDF, is present in a sub- or supercritical state.

[0034] The process of the present invention is typically carried out at a temperature of at least 10°C, preferably at least 25°C, more preferably at least 45°C.

[0035] The pressure is typically maintained at a value above 25 bar, preferably above 50 bar, even more preferably above 75 bar.

[0036] For the purposes of the present invention, the term "non-ionic suspending agent" means a) Polysaccharide derivatives; b) partially hydrolyzed polyvinyl alcohol (PVA); and c) Alkylene oxide polymers (PAOs) It is intended to denote a polymer containing hydroxyl groups selected from the group consisting of:

[0037] The term "polysaccharide derivative" is intended herein to refer to a non-ionic derivative of a hydroxyl-containing polysaccharide polymer that contains as repeating units one or more glycosidic units linked together by glycosidic bonds. A glycosidic unit is intended herein to refer to either a six-membered pyranosidic ring or a five-membered furanosidic ring.

[0038] Preferably, the non-ionic polysaccharide derivative comprises repeating glycoside units selected from D-glucopyranosides and glucofuranosides, or mixtures thereof, linked together by glycosidic bonds.

[0039] More preferably, in the method of the present invention, the nonionic polysaccharide derivatives a) are polysaccharides of formula (I) linked to each other by β-glycosidic bonds: [ka] wherein each R' at each occurrence is equal to or different from every other R' and represents a hydrogen atom, a C1-C8 hydrocarbon group, or a C2-C8 hydroxyalkyl group.

[0040] More preferably, in the carbohydrate derivatives of formula (I), each R', equal to or different from any other, represents a hydrogen atom, a hydroxyethyl group or a 2-hydroxypropyl group.

[0041] More preferably, in the method of the present invention, the carbohydrate derivative of formula (I) is hydroxyethylmethylcellulose or 2-hydroxypropylmethylcellulose, the latter being particularly preferred.

[0042] Non-limiting examples of polysaccharide derivatives a) suitable for the method of the invention include, in particular, cellulose derivatives available under the trade name METHOCEL™ K100, which have a dynamic viscosity of 80 to 120 mPa.s at a concentration of 2% by weight in aqueous solution at 20°C, METHOCEL™ K15M, which have a dynamic viscosity of 11,250 to 21,000 mPa.s at a concentration of 2% by weight in aqueous solution at 20°C, METHOCEL™ K3, which have a dynamic viscosity of 2.4 to 3.6 mPa.s at a concentration of 2% by weight in aqueous solution at 20°C, METHOCEL™ K4M, which have a dynamic viscosity of 3000 to 6000 mPa.s at a concentration of 2% by weight in aqueous solution at 20°C, and CULMINAL™ MHPC5, which have a dynamic viscosity of 4 to 8 mPa.s at a concentration of 2% by weight in aqueous solution at 20°C.

[0043] Partially hydrolyzed polyvinyl alcohol b) is intended herein as an aqueous composition comprising partially hydrolyzed polyvinyl acetate and polyvinyl alcohol.

[0044] Polyvinyl alcohol is commercially available and is available over a range of molecular weights and degrees of hydrolysis.

[0045] Generally, polyvinyl alcohol can be prepared as shown in Scheme 1 below: Scheme 1 [ka] It is prepared by hydrolysis of the polyvinyl alcohol precursor (polyvinyl acetate) obtained from the polymerization of vinyl acetate (CH3COOCHCH2), and the degree of saponification is defined as the degree of hydrolysis (degree of saponification = l / (l+m)).

[0046] The degree of hydrolysis of the PVA used in the aqueous compositions of the present invention is preferably at least 80%.

[0047] The term "alkylene oxide polymer (PAO)" is intended herein to mean a homopolymer or copolymer of a water-soluble non-ionic suspending agent that consists essentially of repeating units derived from linear alkylene oxides.

[0048] Alkylene oxide homo- or copolymers suitable for use in the present invention are typically, but not exclusively, selected from homopolymers consisting of repeat units derived from ethylene oxide (EO), such as polyethylene glycol (also designated PEG, POE or PEO).

[0049] Typically, in the context of the present invention, the average molecular weight (M w ) ranges from 50,000 to 10,000,000 g / mol as measured by techniques known to those skilled in the art, for example by determining the viscosity of their aqueous solutions.

[0050] According to a preferred embodiment, the alkylene oxide polymer (PAO) has the formula (II): R A O-(CH2CH2O) n -R B (II) (In the formula, R A and R B are each independently H or C1 to C5 alkyl, preferably H or CH3, and n is an integer of 1,000 to 200,000, preferably 2,000 to 100,000, more preferably 5,000 to 70,000. It is a polyethylene oxide having the formula:

[0051] Furthermore, according to a more preferred embodiment, the alkylene oxide polymer (PAO) has the formula (IIb): HO-(CH2CH2O) n -H (IIb) (wherein n is an integer of 1,000 to 200,000, preferably 2,000 to 100,000, and more preferably 5,000 to 70,000).

[0052] The at least one ionic carboxyalkyl cellulose B) has the formula [C6-H7-O5-R3] n where R is H or a carboxyalkyl salt, preferably of the formula -CH2-COO-M + where M is an ammonium or alkali metal cation, preferably Na + and Li + and n is an integer of 100 to 5,000.

[0053] The at least non-ionic suspending agent A) is typically present in the polymerization reaction mixture in an amount of 0.01 to 2 g / kg VDF monomer, preferably 0.05 to 0.55 g / kg VDF monomer, more preferably 0.05 to 0.3 g / kg VDF monomer.

[0054] The at least one ionic carboxyalkyl cellulose B) is typically present in the polymerization reaction mixture in an amount of 0.05 to 10 g / kg VDF monomer, preferably 0.3 to 5 g / kg VDF monomer, more preferably 0.5 to 5 g / kg VDF monomer.

[0055] In a preferred embodiment according to the invention, the process is carried out in the presence of A) at least a non-ionic suspending agent and B) at least an ionic carboxyalkyl cellulose, wherein the amount of the at least ionic carboxyalkyl cellulose B) is greater than the amount of the non-ionic suspending agent A).

[0056] More preferably, the amount of the at least one ionic carboxyalkyl cellulose B) in the polymerization is greater than 0.5 g per kg of VDF monomer and the amount of the at least one non-ionic suspending agent A) is less than 0.3 g per kg of VDF monomer.

[0057] The process of the present invention is typically carried out in an aqueous suspension medium in the presence of a radical initiator. While the choice of radical initiator is not particularly limited, it is understood that initiators suitable for the process according to the invention are selected from compounds capable of initiating and / or accelerating the polymerization process.

[0058] Among the radical initiators that can be advantageously used in the method of the present invention, mention may be made of organic radical initiators.Non-limiting examples of suitable organic radical initiators include acetylcyclohexanesulfonyl peroxide; diacetyl peroxydicarbonate; dialkyl peroxydicarbonates, such as diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate; tert-butyl perneodecanoate; tert-amyl perpivalate; 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); tert-butyl perpivalate; dioctanoyl peroxide; dilauroyl peroxide; 2,2'-azobis(2,4-dimethylvaleronitrile); tert-butylazo-2-cyanobenone. Examples of peroxides that may be used include, but are not limited to, hexane; dibenzoyl peroxide; tert-butyl-per-2-ethylhexanoate; tert-butyl permaleate; 2,2'-azobis(isobutyronitrile); bis(tert-butylperoxy)cyclohexane; tert-butyl-peroxyisopropyl carbonate; tert-butyl peracetate; 2,2'-bis(tert-butylperoxy)butane; dicumyl peroxide; di-tert-amyl peroxide; di-tert-butyl peroxide (DTBP); p-methane hydroperoxide; pinane hydroperoxide; cumene hydroperoxide; and tert-butyl hydroperoxide.

[0059] The VDF polymer of the present invention has an intrinsic viscosity measured in N,N-dimethylformamide at 25°C of 0.05 to 0.75 l / g, preferably 0.10 to 0.55 l / g, more preferably 0.13 to 0.45 l / g.

[0060] The Applicant has surprisingly found that the process according to the invention makes it possible to obtain a polymer (VDF) in particulate form which is characterized by excellent flowability, a feature of great importance in industrial processes which have to handle large amounts of VDF polymer in powder form.

[0061] Therefore, in a second aspect, the present invention relates to a vinylidene fluoride polymer [polymer (VDF)] obtainable by the process of the invention.

[0062] In particular, the polymer (VDF) obtained by the process of the present invention is characterized by having a very narrow particle size distribution (PSD) with a D50 value of more than 150 microns.

[0063] The polymer powder obtained by the process of the present invention is also characterized by bead-like, substantially round particles.

[0064] Prior art methods make it possible to obtain particles with a particle size distribution with a D50 value greater than 150 microns only by preparing polymer pellets and then grinding the pellets to obtain the required particle size, however the shape of the ground particles is not round and the surface of the particles is not smooth, so that the particles do not provide any flowability advantage.

[0065] The process of the present invention can obtain bead-like, substantially round particles having a particle size distribution with a D50 value of greater than 150 microns, as shown in Figures 1 and 2, which is clearly different from the particles obtained by grinding pellets according to the prior art process.

[0066] A particularly preferred embodiment of the present invention relates to a polymer (VDF) comprising more than 50 mol %, preferably more than 80 mol % of repeat units derived from the polymerization of vinylidene fluoride monomers, said polymer (VDF) being characterized by having a particle size distribution with a D50 value greater than 250 microns.

[0067] In a third aspect, the present invention relates to a composition [composition (C)] containing at least one polymer (VDF) according to the invention.

[0068] The composition (C) of the present invention may further comprise one or more additives.

[0069] Non-limiting examples of suitable additives include plasticizers such as, for example, dibutyl sebacate.

[0070] In a fourth aspect, the present invention relates to an article comprising the polymer (VDF) or composition (C) as defined above.

[0071] The articles of the present invention are typically obtained by processing the polymer (VDF) or the composition (C) of the present invention as defined above using melt processing techniques such as injection molding or compression molding.

[0072] The articles of the present invention are particularly suitable for use in a variety of applications, such as battery applications.

[0073] In particular, suitable articles comprising the polymer (VDF) or the composition (C) of the invention as defined above are components for secondary batteries, such as electrodes and / or separators, in particular in lithium ion batteries.

[0074] The polymer (VDF) of the invention or composition (C) as defined above is particularly suitable as a binder in electrodes for secondary batteries, in particular lithium ion batteries.

[0075] Furthermore, the polymer (VDF) of the present invention or the composition (C) defined above may be - at least one substrate layer, preferably made of at least one polyolefin; - at least one layer attached to said substrate layer, preferably comprising, preferably consisting of, at least one polymer of the invention (VDF); The present invention is particularly suitable for use in separators, e.g., composite separators, for secondary batteries, particularly lithium ion batteries, comprising:

[0076] Furthermore, another object of the present invention is the use of the polymer (VDF) or the composition (C) as defined above for the manufacture of a hydrophilic membrane.

[0077] The present invention therefore relates to a method for producing a hydrophilic membrane comprising the polymer (VDF) or the composition (C) as defined above, and to a hydrophilic membrane comprising the polymer (VDF) or the composition (C).

[0078] The uses, methods for producing hydrophilic membranes and membranes therefrom detailed above are described in detail in relation to the polymer (VDF); nevertheless, it is understood that the composition (C) as detailed above can be used in place of the polymer (VDF) in all of the embodiments detailed below.

[0079] For purposes of the present invention, the term "membrane" has its ordinary meaning, i.e., it refers essentially to a discrete, generally thin interface that regulates the permeation of chemical species in contact with it. This interface may be molecularly uniform (i.e., completely uniform in structure) (dense membrane) or chemically or physically heterogeneous, for example, containing gaps, voids, or pores of finite dimensions (porous membrane). The terms "pore," "void," and "void" are used synonymously within the context of the present invention.

[0080] The membranes of the present invention are preferably porous membranes. Porous membranes generally have a voided structure with interconnected pores.

[0081] Porous membranes are generally characterized by their average pore size (d) and porosity (ε), ie, the fraction of the total membrane that is porous.

[0082] The porous membrane of the invention advantageously has a porosity (ε) of at least 1%, preferably at least 2%, more preferably at least 3%, and advantageously at most 90%, preferably at most 80%. The pores generally have an average diameter (d) advantageously of at least 0.01 μm, preferably at least 0.05 μm, more preferably at least 0.1 μm, and advantageously at most 50 μm, preferably at most 25 μm, more preferably at most 10 μm.

[0083] Membranes can be in the form of flat sheets or can be manufactured in the form of thin-walled tubes or fibers (hollow fiber membranes). Flat sheet membranes are generally preferred when high flux is required. Formation of membranes into hollow fibers is particularly advantageous when compact modules containing large surface areas are required.

[0084] The membranes of the present invention may be used, for example, in the chemical processing industry in various separation processes such as microfiltration and preferably ultrafiltration, especially of aqueous media, in biomedical applications, e.g., for hemodialysis, for controlled release of drugs, for artificial organs such as kidneys, lungs and pancreas, and in membrane bioreactors for municipal and industrial wastewater treatment.

[0085] When the membrane is a dense membrane, the process of the invention advantageously comprises a step of casting and / or melt-forming a polymer (VDF) as defined above. Melt-forming is generally used to produce dense membranes either by extrusion from a die as a sheet or as a blown film.

[0086] When the membrane is a porous membrane, the method of the present invention advantageously comprises at least one step comprising one of the following techniques: irradiation, film expansion, mold leaching, solution precipitation, electrospinning.

[0087] The disclosures of patents, patent applications, and publications incorporated herein by reference should conflict with the specification of this application to the extent that the terms may be ambiguous, but the specification shall control.

[0088] The invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and not intended to limit the scope of the invention.

[0089] raw materials (B-1): Sodium carboxymethylcellulose with an average molecular weight of 250,000 g / mol, commercially available from Sigma Aldrich.

[0090] (B-2): Sodium carboxymethylcellulose with an average molecular weight of 90,000 g / mol, commercially available from Sigma Aldrich.

[0091] (A-1): Hydroxypropyl methylcellulose ether commercially available from Dow Chemical under the name "Methocel (registered trademark) K100GR" having a dynamic viscosity of 80 to 120 mPa·s at 20°C in an aqueous solution with a concentration of 2% by weight.

[0092] (A-2): PVA commercially available under the name Alcotex® 80 (Synthomer), which is an 80% hydrolyzed high molecular weight polyvinyl alcohol.

[0093] DCE: Diethyl carbonate from Sigma Aldrich.

[0094] Determining the intrinsic viscosity of polymers The intrinsic viscosity (η) [dl / g] was calculated using an Ubbelhode viscometer based on the dropwise addition time at 25°C of a solution obtained by dissolving the polymer in N,N-dimethylformamide at a concentration of about 0.2 g / dl, according to the following formula:

number

[0095] Example 1: In a 4 L reactor equipped with an impeller rotating at 650 rpm, the following were introduced in succession: 1,950 g of demineralized water, 0.08 g of (A-1) per kg of total VDF monomers, 0.93 g of (B-1) per kg of total VDF monomers, and 371.5 g of calcium hydroxide solution from Sigma Aldrich.

[0096] The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purge at a fixed temperature of 14° C. This sequence was repeated three times.

[0097] Then, 40 g of demineralized water, 5.1 g of hydrogen peroxide (Brenntag), 15.27 g of DCE, and 1.59 g of ethyl chloroformate (Framochem) were introduced into the reactor.

[0098] After 15 minutes, 1,004 g of VDF was added to the mixture at an agitation speed of 880 rpm. The reactor was then gradually heated until a first setpoint temperature of 41.5 °C was reached, corresponding to a reactor pressure of 83 bar. The pressure was constantly maintained at 83 bar by adding 295 g of VDF. After this addition, no further monomer was added, and the pressure began to drop to 57 bar. The reactor was then gradually heated to 61 °C. At this point, the pressure also began to drop. When the pressure had dropped to 20 bar, the reaction was stopped by degassing the suspension until atmospheric pressure was reached. A total of 1,300 g of VDF was added to the reactor. The polymer was then recovered by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried in a fluidized bed dryer (Retsch) at 60 °C for 3 hours. 1,236 g of dry powder was recovered.

[0099] In general, more than 90% conversion of VDF was achieved in all working embodiments.

[0100] The polymerization time, particle characterization and flowability are shown in Table 1.

[0101] Example 2 Comparison: The same procedure as in Example 1 was carried out, except that only 0.46 g of (A-1) per kg of total VDF monomer was added to the reactor, and no (B-1) was added.

[0102] 1,249 g of dry powder was recovered.

[0103] The polymerization time, particle characterization and flowability are shown in Table 1.

[0104] Example 3: The same procedure as in Example 1 was carried out, but with 0.08 g of (A-1) per kg of total VDF monomers and 0.46 g of (B-1) per kg of total VDF monomers.

[0105] The polymerization time, particle characterization and flowability are shown in Table 1.

[0106] Example 4 Comparison: The same procedure as in Example 1 was carried out, except that only 0.09 g of (A-1) per kg of total VDF monomer was added to the reactor, and no (B-1) was added.

[0107] The suspension proved to be very unstable and the reactor had to be vented after 67 minutes, resulting in no efficient polymerization. This precludes the scale-up of the process to industrial production.

[0108] The polymerization time, particle characterization and flowability are shown in Table 1.

[0109] Example 5 Comparison: The same procedure as in Example 1 was carried out, but only 1.19 of (B-1) was added per kg of total VDF monomer, and no (A-1) was added.

[0110] The suspension proved to be very unstable and the reactor had to be vented after 114 minutes, resulting in no efficient polymerization. This precludes the scale-up of the process to industrial production.

[0111] The polymerization time, particle characterization and flowability are shown in Table 1.

[0112] Example 6: The same procedure as in Example 1 was carried out, but with the addition of 0.08 g of (A-1) per kg of initial VDF monomer and 0.93 g of (B-2) per kg of total VDF monomer.

[0113] The polymerization time, particle characterization and flowability are shown in Table 1.

[0114] Example 7: 2,239 g of demineralized water, 0.07 g of (A-1) per kg of total VDF monomers, and 0.80 g of (B-1) per kg of total VDF monomers were sequentially introduced into a 4 L reactor, and the mixture was stirred with an impeller rotating at a speed of 880 rpm.

[0115] The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purge at a fixed temperature of 14° C. This sequence was repeated three times.

[0116] Then, 20 g of DCE and 1.47 g of a solution (75%) of initiator t-amyl perpivalate (United Initiators) in isododecane were introduced into the reactor.

[0117] 1,053 g of VDF were introduced into this mixture. The reactor was then gradually heated until a first set point temperature of 52° C. was reached. At this temperature, the reactor pressure was fixed at 120 bar.

[0118] The pressure was kept constant at 120 bar by feeding 244 g of VDF. After this feeding, no further monomer was fed and the pressure began to decrease to 90 bar. The reactor was then gradually heated at 67 °C. The pressure was kept at 80 bar and 281 g of VDF was fed into the reactor. When the pressure had decreased to 55 bar, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached. A total of 1,580 g of VDF was charged into the reactor. The polymer was then recovered by filtration and suspended in clean water in a stirred tank. After a washing treatment, the polymer was dried in a fluidized bed dryer (Retsch) at 60 °C for 3 hours.

[0119] 1,414 g of dry powder was recovered.

[0120] The polymerization time, particle characterization and flowability are shown in Table 1.

[0121] Example 8: Into a 4 L reactor were introduced 2,542 g of demineralized water, 0.06 g of (A-1) per kg of total VDF monomers, and 0.68 g of (B-1) per kg of total VDF monomers, and the mixture was stirred with an impeller rotating at a speed of 880 rpm.

[0122] The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purge at a fixed temperature of 14° C. This sequence was repeated three times.

[0123] Then, 9.5 g of DCE and 1.33 g of a solution of initiator t-amyl perpivalate (United Initiators) in isododecane (75%) were introduced into the reactor.

[0124] 820 g of VDF was introduced into this mixture. The reactor was then gradually heated until a first set point temperature of 52° C. was reached. At this temperature, the reactor pressure was fixed at 120 bar.

[0125] During the polymerization, a total of 631 g of VDF was fed, keeping the pressure constant at 120 bar. After this feed, no further monomer was fed and the pressure began to decrease to 95 bar. The reactor was then gradually heated at 65°C. At this point, the pressure also began to decrease. When the pressure had dropped to 46 bar, the reaction was stopped by degassing the suspension until atmospheric pressure was reached. A total of 1,450 g of VDF was then charged to the reactor. The polymer was then recovered by filtration and suspended in clean water in a stirred tank. After a washing treatment, the polymer was dried in a fluidized bed dryer (Retsch) at 60°C for 3 hours.

[0126] 1,288 g of dry powder was recovered.

[0127] The polymerization time, particle characterization and flowability are shown in Table 1.

[0128] Example 9: In a 4 L reactor, 1,714 g of demineralized water, 0.1 g of (A-1) per kg of total monomers, and 1.2 g of (B-1) per kg of total monomers were introduced, and the mixture was stirred with an impeller rotating at a speed of 880 rpm.

[0129] The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purge at a fixed temperature of 14° C. This sequence was repeated three times.

[0130] Next, 0.55 g of acrylic acid (AA) and 4.94 g of a solution (75%) of initiator t-amyl perpivalate (United Initiators) in isododecane were introduced into the reactor. 1,279 g of VDF was introduced into this mixture. The reactor was then gradually heated until a set point temperature of 55° C. was reached, which corresponded to a pressure of 120 bar.

[0131] The pressure was kept constant throughout the polymerization at 120 bar by feeding an aqueous solution containing 14.91 g of AA per liter of solution. After 405 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached. A total of 909 g of AA solution was charged into the reactor.

[0132] The polymer was then recovered by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried in a fluidized bed dryer (Retsch) at 60°C for 3 hours. 974 g of dry powder was recovered.

[0133] The polymerization time, particle characterization and flowability are shown in Table 1.

[0134] Fluidity Test: The flowability of the dry powders obtained in Examples 1 to 10 was evaluated in accordance with ASTM D 1895 standard for powders.

[0135] 50 g of dry polymer powder was weighed on a precision balance. This powder was then shaken by hand for 5 minutes in a stainless steel cylindrical container measuring 3.99 x 7.98 cm. The resulting powder was placed in a closed Inox funnel (11.4 cm in size, with an opening diameter of 9.3 cm) placed at a height of 12 cm in a saucer cup. The powder was then released, and the time required for the powder to flow was monitored with a stopwatch. If the powder did not flow well, the funnel was tapped until the sample flowed completely. The powder collected in the cup was reweighed on a precision balance. The time and amount of powder that flowed, as well as its aspect and whether or not the powder needed to be assisted to flow, were recorded.

[0136] D50: Particle size analysis of powders was performed using laser diffraction according to the ISO 13320 standard. D50 indicates the particle size below which half of the population lies and above which half lies.

[0137] The particle size distribution (PSD) of the population was assessed by measuring SPAN.

[0138] SPAN is as follows:

number

[0139] The results are shown in Table 1 below.

[0140] [Table 1]

[0141] As shown in Table 1, the process of the present invention has been found to advantageously yield VDF polymers, as particularly exemplified by the polymers obtained according to the process of any one of Examples 1, 3, and 6-9, which exhibit large polymer powders and at the same time narrow PSDs.

[0142] In particular, the VDF polymers of Examples 1 and 6, which have particularly large particle sizes of more than 250 μm, show excellent flowability, whereas the processes for producing the polymers of Comparative Examples 2, 4 and 5, which used only non-ionic or ionic suspending agents, resulted in dry polymers with smaller particle sizes, or polymerizations that were uncontrollable due to the absence of a stable suspension, which led to the formation of polymer blocks in the reactor.

Claims

1. 1. A process for the preparation of vinylidene fluoride polymers [polymer(VDF)] in aqueous suspension, said process comprising: A) at least a non-ionic suspending agent; and B) at least an ionic carboxyalkyl cellulose and polymerizing in the presence of said non-ionic suspending agent A) is present in the polymerization reaction mixture in an amount of 0.05 to 0.55 g per kg of VDF monomer, said ionic carboxyalkyl cellulose B) being present in the polymerization reaction mixture in an amount of 0.3 to 5 g per kg of VDF monomer; The method of claim 1, wherein the amount of said ionic carboxyalkyl cellulose B) is greater than the amount of said non-ionic suspending agent A).

2. The non-ionic suspending agent is a) polysaccharide derivative; b) partially hydrolyzed polyvinyl alcohol (PVA); and c) Alkylene Oxide Polymers (PAOs) 10. The method of claim 1, wherein the polymer is a hydroxyl-containing polymer selected from the group consisting of:

3. The polysaccharide derivatives are linked to each other by β-glycosidic bonds, and have the formula (I): 【Chemistry 1】 wherein each R′ at each occurrence is equal to or different from every other R′ and is a hydrogen atom, C １ ~C ８ Hydrocarbon group or C ２ ~C ８ 3. The method of claim 2, wherein the carbohydrate comprises repeating β-D-glucopyranoside units of the formula (I) and (II), wherein the repeating β-D-glucopyranoside units represent hydroxyalkyl groups.

4. 4. The method of claim 3, wherein the carbohydrate comprising repeating β-D-glucopyranoside units of formula (I) is hydroxyethyl methylcellulose or 2-hydroxypropyl methylcellulose.

5. 3. The method of claim 2, wherein the partially hydrolyzed polyvinyl alcohol (PVA) is, as an aqueous composition, partially hydrolyzed polyvinyl acetate and polyvinyl alcohol having a degree of hydrolysis of at least 80%.

6. The alkylene oxide polymer (PAO) has the formula (IIb): HO-(CH ２ CH ２ O) ｎ -H (IIb) 3. The method of claim 2, wherein the polyethylene glycol has the formula: wherein n is an integer from 1,000 to 200,000.

7. 7. The process according to claim 1, wherein the non-ionic suspending agent A) is present in the polymerization reaction mixture in an amount of 0.05 to 0.3 g per kg of VDF monomer.

8. 8. The process according to any one of claims 1 to 7, wherein the ionic carboxyalkyl cellulose B) is present in the polymerization reaction mixture in an amount of 0.5 to 5 g per kg of VDF monomer.

9. 9. The process according to claim 1, wherein the amount of ionic carboxyalkyl cellulose B) in the polymerization is more than 0.5 g per kg of VDF monomer and the amount of non-ionic suspending agent A) is less than 0.3 g per kg of VDF monomer.

Images