WO2011058016A1

WO2011058016A1 - Process for manufacturing grafted polymers

Info

Publication number: WO2011058016A1
Application number: PCT/EP2010/067133
Authority: WO
Inventors: Fabrizio Spada; Bradley Lane Kent; Shiow-Ching Lin
Original assignee: Solvay Solexis S.P.A.
Priority date: 2009-11-13
Filing date: 2010-11-09
Publication date: 2011-05-19

Abstract

The invention pertains to a method for manufacturing a dispersions of a grafted copolymer, said method comprising: providing a dispersion of particles at least one vinylidene fluoride (VDF) polymer [polymer (F)] in a liquid medium comprising at least one latent solvent for polymer (F), wherein said polymer (F) is substantially insoluble at a temperature of 25°C in said liquid medium; reacting in said liquid medium said polymer (F) with an ATRP catalyst comprising at least one transition metal salt and at least one ligand and with an ethylenically unsaturated comonomer [comonomer (A)] at a temperature higher than 25°C wherein said polymer (F) is at least partially swelled in said liquid medium; cooling said liquid medium so as to obtain a dispersion of particles of grafted copolymer of polymer (F) and comonomer (A).

Description

Process for manufacturing grafted polymers

Technical Field

[0001] This application claims priority to U.S. provisional application No.

61/261 185 filed on November 13, 2009, the whole content of this application being incorporated herein by reference for all purposes.

[0002] This invention pertains to a process for manufacturing grafted polymers enabling maintaining native morphology of the parent polymer.

Background Art

[0003] Vinylidene fluoride (VDF) polymers are fluoropolymers known to possess unique properties such as low surface energy, high chemical and thermal stability, and good mechanical properties. Such VDF polymers have been widely used for various applications including chemically resistant materials, filter membranes, electrical insulators, and the like. However, VDF polymers are normally highly hydrophobic and solvophobic, and present certain disadvantages, such as poor wettability, and miscibility. These problems might possibly limit their application in certain fields.

[0004] The development of graft copolymers afforded a possibility to overcome many of the disadvantages discussed above. Indeed, properties such as wettability, amphiphilicity, biocompatibility, solubility, phase compatibility with other polymers, and adhesion to surfaces can be improved by graft copolymerization of co-monomers onto the backbone of VDF polymers. Depending on the nature of the co-monomer, graft copolymers may possess specific properties while retaining desirable properties of the parent VDF polymer.

[0005] The synthesis of graft copolymers is most commonly accomplished via free-radical reactions initiated by exposing the VDF polymer to ionizing radiation and/or a free-radical initiator in the presence of the comonomer. Free radical syntheses in this manner, however, can be an uncontrolled process. Numerous radicals are present not only on the polymer but also on the comonomer, which can undergo free-radical homopolymerization resulting in a mixture of homopolymers and graft copolymers. Thus, a significant disadvantage of these free-radical techniques is that the product is typically a mixture of graft copolymer and homopolymer.

Moreover, polymer backbone degradation and/or crosslinking can occur as a result of uncontrolled free-radical production, dramatically affecting properties of the parent VDF polymers.

[0006] For overcoming these issues, grafting methods have been developed

involving reactions known as atom transfer radical polymerization (ATRP), which is a "controlled" free-radical polymerization. This reaction is controlled because free radical concentration is kept low and mainly centred on the parent polymer, preventing the occurrence of numerous undesired reactions.

[0007] Thus, document WO 02/22712 (MASSACHUSETTS INST TECHNOLOGY ) 21.03.2002 pertains to a method for grafting hydrophilic chains into polymers, including PVDF, by graft polymerization of vinyl monomers by ATRP. PVDF grafted with methacrylic acid was thus obtained by solution-polymerizing PVDF and terbutylmethacrylate in NMP in the presence of an ATRP catalyst, precipitating the grafted polymer and hydrolizing the same with toluensulphonic acid.

[0008] Similarly, documents WO 2007/1 17493 (UNIV MASSACHUSETTS)

18.10.2007 and ZHANG, Mingfu, et al. Graft Copolymers from

Poly(vinylidene fluoride-co-chlorotrifluoroethylene) via Atom Transfer radical Polymerization. Macromolecules. 2006, vol.39, no.10,

p.3531 -3539. disclose a method for graft-polymerizing fluoropolymers comprising recurring units derived from chlorortrifluoroethylene (CFTE) with vinyl monomers, such as styrene, terbutylacrylate by ATRP

technique. Need of ensuring a homogeneous reaction system wherein both the polymer and the ATRP catalyst are in solution is mentioned. In particular, former document teaches that homopolymers of CTFE are not suitable for this grafting process because of their insolubility, while copolymers of VDF and CTFE, which can be dissolved in polar organic solvents, make the radical graft polymerization possible.

[0009] Finally, PATEL, R., et al. Composite polymer electrolyte membranes

comprising P(VDF-co-CTFE)-g-PSSA graft copolymer and zeolite for fuel cell applications. Polym. Adv. Techno/. (2009) published online DOI: 10, 1002/pat. 1390. 2009. discloses a process for grafting 4-styrene-sulphonic acid by ATRP onto SOLEF® 31508 VDF-CTFE copolymer, in a reaction medium made of a mixture of NMP and DMSO, wherein said copolymer is solubilised.

[0010] Nevertheless, in the methods of the prior art, solubilization of the VDF polymer in a suitable solvent is taught as an essential pre-requisite for effective grafting. As a consequence, burdensome techniques have to be applied for the recovery and separation of the grafted copolymer from reaction medium. Moreover, these methods fail to preserve particle morphology of parent VDF polymers when provided under the form of particles, e.g. obtained from emulsion or dispersion polymerization.

Grafting methods of the prior art cannot thus provide dispersions suitable for e.g. coating applications.

[001 1] It is well known that for proper formulation of paints comprising VDF

polymers, generally in admixture with (meth)acrylic resins, optical properties (e.g. gloss) can be optimized when increasing compatibility among the VDF polymer and the hydrogenated resin. Furthermore, while solvent resistance of coatings from hydrogenated resins and VDF polymers can be obtained by crosslinking, lack of cure site on VDF polymers might brought to 'disrupted' multiphase coatings, wherein the advantages of crosslinking are lost.

[0012] There is thus still a shortfall in the art for PVDF polymers suitable for

manufacturing paints, thus possessing appropriate particle morphology for being easily dispersed in a coating composition so as to provide

appropriate liquid viscosity, but also possessing increased compatibility towards hydrogenated polymers and/or crosslinking sites for taking part in crosslinking reactions in combination with thermosetting resins.

Disclosure of Invention

[0013] It is thus an object of the present invention a method for manufacturing a dispersions of a grafted copolymer, said method comprising:

- providing a dispersion of particles at least one vinylidene fluoride (VDF) polymer [polymer (F)] in a liquid medium comprising at least one latent solvent for polymer (F), wherein said polymer (F) is substantially insoluble at a temperature of 25°C in said liquid medium;

- reacting in said liquid medium said polymer (F) with an ATRP catalyst comprising at least one transition metal salt and at least one ligand and with at least one ethylenically unsaturated comonomer [comonomer (A)] at a temperature higher than 25°C wherein said polymer (F) is at least partially swelled in said liquid medium;

- cooling said liquid medium so as to obtain a dispersion of particles of grafted copolymer of polymer (F) and comonomer (A).

[0014] The Applicant has surprisingly found that latent solvents for polymer (F), while failing to effectively solubilise polymer (F), indeed advantageously act as suitable reacting media for enabling graft polymerization by ATRP to take place.

[0015] As a consequence, native morphology of polymer (F) can be effectively maintained, enabling easy recovery of particles of grafter polymer.

[0016] Thus, coating compositions can be obtained combining easiness in

processing of native VDF dispersions and advantages of grafted materials, like, e.g. increased compatibility with hydrogenated resins and possibility of providing active sites for further crosslinking, enabling increased hardness and solvent resistance.

[0017] Within the context of the present invention, the expression "graft

copolymer" is intended to denote a copolymer obtained by covalently bonding a species to be grafted, referred to as a comonomer, to a parent polymer which provides the backbone in the graft copolymer.

[0018] The product resulting from the method of this invention is thus a graft

copolymer which comprises at least one comonomer (A) covalently attached to the parent polymer (F). Typically, the graft copolymer comprises the same backbone as the parent polymer (F). The graft copolymer generally differs from the parent polymer (F) in that the graft copolymer has a plurality of side chains protruding from the backbone. If reactive sites from which side chainsstem were present in the parent at regular intervals, the graft copolymer can result in side chains spaced at substantially regular intervals. Such graft copolymers resemble a comb and are accordingly termed "comb polymers." [0019] The polymer (F) is typically a polymer comprising :

(a') at least 60 % by moles, preferably at least 75 % by moles, more preferably 85 % by moles of vinylidene fluoride (VDF);

(b') optionally from 0.1 to 15%, preferably from 0.1 to 12%, more preferably from 0.1 to 10% by moles of a fluorinated monomer different from VDF; said fluorinated monomer being preferably selected in the group consisting of vinylfluoride (VF-|), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE),

perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixtures therefrom; and

(c') optionally from 0.1 to 5 %, by moles, preferably 0.1 to 3 % by moles, more preferably 0.1 to 1 % by moles, based on the total amount of monomers (a') and (b'), of one or more hydrogenated comonomer(s).

[0020] The polymer (F) is preferably a polymer consisting essentially of :

perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixtures therefrom.

[0021] End groups, defects and might be present, without this affecting properties of the polymer (F).

[0022] Polymer (F) may still comprise other moieties such as defects,

end-groups, minor amounts (< 1 % by moles with respect to total number of moles of recurring units (a') and (b')) of recurring units derived from other monomers, and the like, which do not affect nor impair its physico -chemical properties.

[0023] While ATRP can be effectively initiated by secondary fluorine moieties of VDF recurring units, it is nevertheless generally preferred that the polymer (F) comprises recurring units containing at least one secondary halogen atom selected from CI, Br and I, preferably CI.

[0024] In preferred embodiments, nevertheless, the polymer (F) comprises

recurring units derived from chlorotrifluoroethylene (CTFE).

[0025] A particularly preferred polymer (F) is a copolymer of VDF and CTFE, possibly comprising recurring units derived from fluorinated monomer different from VDF and CTFE, as listed above under (b'), and generally in amounts as above defined.

[0026] The term 'particles' has its usual meaning and it is used for designating discrete three-dimensional solids.

[0027] Particles of polymer (F) to be used in the process of the invention are

generally obtained by coagulation of polymer (F) lattices. Particles of polymer (F) are thus generally composed of agglomerates of primary particles having an average primary particle size of 10 to 500 nm, preferably of 50 to 450 nm, even more preferably of 150 to 350 nm.

[0028] For the purpose of the invention, the term "liquid medium" is intended to denote a medium which is available in liquid state at a temperature of 25°C.

[0029] By the term "dispersion" is meant that the polymer (F) particles are stably dispersed in the liquid medium, so that neither solvation of the particles nor settlement into cake within time of use does occur.

[0030] The expression 'substantially insoluble' is understood to mean that the polymer (F) is optionally solubilised in the liquid medium at a concentration of less than 1 g/l, preferably of less than 0.5 g/l, more preferably of less than 0.1 g/l; most preferably the solubilised fraction is absent.

[0031] The liquid medium comprises at least one latent solvent for polymer (F).

[0032] A latent solvent for the polymer (F) is a solvent which does not dissolve or substantially swell polymer (F) at 25°C, which solvates polymer (F) at its boiling point, but on cooling, polymer (F) precipitates.

[0033] A solvent will be considered as not dissolving the polymer (F) when the polymer (F) cannot be solubilised in said solvent at a concentration exceeding 1 g/l, preferably exceeding 0.5 g/l, more preferably exceeding 0.1 g/l, even more preferably exceeding 0.01 g/l.

[0034] Latent solvent suitable for the process of the invention are notably methyl isobutyl ketone, n-butyl acetate, cyclohexanone, diacetone alcohol, diisobutyl ketone, ethyl acetoacetate, triethyl phosphate, propylene carbonate, triacetin (also known as 1 ,3-diacetyloxypropan-2-yl acetate), dimethyl phthalate, glycol ethers based on ethylene glycol, diethylene glycol and propylene glycol, and glycol ether acetates based on ethylene glycol, diethylene glycol and propylene glycol.

[0035] Non limitative examples of glycol ethers based on ethylene glycol,

diethylene glycol and propylene glycol are notably ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, propylene glycol methyl ether, propylene glycol dimethyl ether, propylene glycol n-propyl ether.

[0036] Non limitative examples of glycol ether acetates based on ethylene glycol, diethylene glycol and propylene glycol are notably ethylene glycol methyl ether acetate, ethylene glycol monethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol methyl ether acetate.

[0037] A particularly preferred latent solvent is dimethyl phthalate.

[0038] The liquid medium can comprise additional solvents, provided that polymer (F) remains substantially insoluble at a temperature of 25°C in said liquid medium.

[0039] The liquid composition can thus further comprise at least one among

intermediate solvent for polymer (F) and non-solvent for polymer (F).

Mixtures of one or more than one latent solvent with one or more than one intermediate solvent and/or non-solvent can also be used.

[0040] An intermediate solvent for the polymer (F) is a solvent which does not dissolve or substantially swell the polymer (F) at 25°C, which solvates polymer (F) at its boiling point, and retains polymer (F) in solvated form, i.e. in solution, upon cooling.

[0041] A non-solvent for polymer (F) is a solvent which does not dissolve or

substantially swell the polymer (F).

[0042] Non-solvents suitable for the process of the invention are notably methanol, hexane, toluene, ethanol and xylene.

[0043] Intermediate solvents suitable for the process of the invention are notably butyrolactone, isophorone and carbitol acetate.

[0044] Nevertheless, preferred embodiments are those wherein the liquid medium consist essentially of at least one latent solvent as above described. Minor amounts (less than 5 % wt, preferably less than 1 % wt) of other ingredients/impurities might be present, without properties of the liquid medium being affected.

[0045] Choice of the ethylenically unsaturated comonomer [comonomer (A)] is not particularly limited and will be done by the skilled in the art by reference to properties of polymer (F) to be modified.

[0046] Sequential use of two or more such comonomers (A) can provide block graft copolymers with corresponding side chains, properties and structure.

[0047] Among comonomer (A) suitable for the process of the invention mention can be made of styrene monomers, (meth)acrylic monomers, chlorinated monomers, functional fluoromonomers, and the like.

[0048] Among styrene monomers, mention can be made of styrene, and

corresponding alkyl, aryl, vinyl-substituted counterparts.

[0049] Among (meth)acrylic monomers, mention can be made of acrylic acid and its ester derivatives, including functional derivatives, methacrylic acid and its ester derivatives, including functional derivatives, acrylonitrile, acrylamides, methacrylamides.

[0050] Among halogenated monomers, mention can be made of vinyl halides such as vinyl chloride; of vinylidene halides such as vinylidene chloride.

[0051] Among functional fluoromonomers, mention can be made of:

- sulphonyl fluoride (per)fluoroolefins of formula: CF2=CF(CF2)_nSO2F wherein n is an integer between 0 and 6, preferably n is equal to 2 or 3 ;

- sulphonyl fluoride (per)fluorovinylethers of formula: CF2=CF-O-(CF2)_m SO₂F

wherein m is an integer between 1 and 10, preferably between 1 and 6, more preferably between 2 and 4, even more preferably m equals 2;

- sulphonyl fluoride (per)fluoroalkoxyvinylethers of formula:

CF₂=CF-(OCF2CF(RF₁))_w-O-CF2(CF(RF2))ySO₂F wherein w is an integer between 0 and 2, RFi and RF2, equal or different from each other, are independently -F, -CI or a C1-10 perfluoroalkyl group, optionally substituted with one or more ether oxygens, y is an integer between 0 and 6; preferably w is 1 , RFi is -CF3, y is 1 and RF2 is -F; - sulphonyl fluoride aromatic (per)fluoroolefins of formula CF2=CF-Ar-SO2 F

wherein Ar is a C5-15 aromatic or heteroaromatic substituent.

[0052] According to a preferred embodiment, the comonomer (A) is a

(meth)acrylic monomer of formula:

wherein:

each of R'i , R'2, R'3, equal to or different from each other, is

independently a hydrogen atom or a C1-C3 hydrocarbon group, and R'4 is a hydrogen atom or a C1 -C3 hydrocarbon group, optionally comprising one or more functional groups selected from -OH, -N(R'5)3, wherein each of R' 5, equal to or different from at each occurrence, is independently a hydrogen atom or a C-|-C6 hydrocarbon group, an epoxy group, an isocyanate group, a carboxylic group (in its acid, ester or amide form).

[0053] According to a more preferred embodiment, the comonomer (A) is a

hydrophilic (meth)acrylic monomer (MA) of formula:

wherein each of R1 , R2, R3, equal to or different from each other, is independently a hydrogen atom or a C1-C3 hydrocarbon group, and ROH is a hydrogen or a C1 -C5 hydrocarbon moiety comprising at least one hydroxyl group.

Non limitative examples of hydrophilic (meth)acrylic monomers (MA) are notably acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate; hydroxyethylhexyl(meth)acrylates.

The monomer (MA) is more preferably selected among:

- hydroxyethylacrylate (HEA) of formula:

- hydroxyethylmethacryl ula:

2-hydroxypropyl acrylate (HPA) of either of formulae:

2-hydroxypropyl methacrylate (HPMA) of either c

- acrylic acid (AA);

- methacrylic acid (MA);

- and mixtures thereof.

The ATRP catalyst comprises generally at least one transition metal and at least one ligand. The ATRP catalyst can be provided to the process of the invention as pre-formed complex of comprising one or more transition metal(s) and one or more ligand(s) or can be formed in situ in the liquid medium by separate addition of one or more transition metal compound(s) and one or more ligand(s).

[0057] Transition metals comprised in the ATRP catalysts are generally selected in view of their redox chemistry, as they shall act advantageously as one electron oxidants/reductants.

[0058] Redox couples of transition metals which have been successfully applied in ATRP catalysts are notably Mo^lv-Mo^v, Mn^M-Mn^IM, Re^v-Re^vl, Fe^M-Fe^MI,

Fe'-Fe", Co°-Co', Ni^M-Ni^MI, Pd^M-Pd^MI, Cu'-Cu", Ru^M-Ru^IM. ATRP catalysts based on Cu'-Cu" and Ru"-Ru'" are preferred.

[0059] The transition metal is thus preferably Copper or Ruthenium, more

preferably Copper.

[0060] Copper (I) salts are particularly suitable for being used as catalyst

components in the process of the present invention.

[0061] Should the ATRP catalyst comprise Copper as transition metal, said ATRP catalyst generally comprises at least one Copper (I) salt and at least one mono- or multi-dentate amine or nitrogenous ligand.

[0062] Copper (I) salt is generally a Copper (I) halide, preferably Copper (I)

chloride.

[0063] The mono- or multi-dentate amine or nitrogenous ligand can be selected from 2,2'-bipyridine and 2,2'-bipyridines substituted at either one or both of the 4 and 4'-positions with one or more alkyl moieties, ethylenediamine, diethylenetriamine, and triethy lenetetramine, each of which can comprise at least one N-substituent independently selected from alkyl, cycloalkyl, and aryl substituents. Examples of such substituted bipyridine ligands include 4,4'-dimethyl-2,2'-bipyridine, 4,4'-di(5-nonyl)-2,2'-bipyridine and various other bipyridyl ligands comprising one or more such alkyl substituents. Such multi-dentate amine ligands can include

tetramethylethylenediamine, tetraethylethylenediamine,

ditertbutylethylenediamine, 1 ,1 ,4,7,7-pentamethyldiethylenetriamine, 1 , 1 ,4,7,7- pentabutyldiethylenetriamine, and 1 ,1 ,4,7,10,10- hexamethyltriethylenetetramine.

[0064] Polymer (F) is reacted with an ATRP catalyst and with at least one

comonomer (A) at a temperature higher than 25°C.

[0065] Generally the temperature is higher than 40°C, preferably higher than 50°C, more preferably higher than 60°C.

[0066] Upper temperature limit is not particularly limited; it is nevertheless

understood that the temperature will be selected as to remain below melting point of polymer (F). This temperature will be generally below 170°C, preferably below 150°C, more preferably below 130°C.

[0067] In these reaction conditions, polymer (F) is at least partially swelled in the liquid medium.

[0068] The expression 'at least partially swelled' is understood to mean that the volume of the polymer (F) undergoes an increase, typically of at least 5 %, preferably of at least 10 %, more preferably of at least 15 %, with respect to the initial volume of the polymer (F) itself in dry form.

[0069] Without being bound by this theory, the Applicant believes that this

swelling phenomenon is advantageously due to the interpenetration of the liquid medium within the macromolecules of the polymer (F), and that this intimate contact among the polymer (F) and the liquid medium enables achieving adequate reactivity in ATRP, without nevertheless dramatically affecting particles morphology.

[0070] The liquid medium is finally cooled so as to obtain a dispersion of particles of grafted copolymer of polymer (F) and comonomer (A).

[0071] Cooling can be effected by any mean. Typically, liquid medium is cooled under stirring, generally without using any external cooling mean, i.e. by simply letting the liquid medium coming naturally back to room

temperature.

[0072] Recovery of the dispersion of particles of grafted copolymer of polymer (F) and comonomer (A) is thus possible.

[0073] Possibly, particles of grafted copolymer of polymer (F) and comonomer (A) can be separated from liquid medium by known techniques, like notably, filtration, sedimentation, and centrifugation.

[0074] Particles of grafted copolymer of polymer (F) and comonomer (A) so

obtained can be then further used, e.g. for the formulation of paints and coating compositions.

[0075] The invention is further directed to a composition comprising particles of at least one grafted copolymer of polymer (F) and comonomer (A) in a liquid medium comprising at least one latent solvent, as above described, said particles being agglomerates of primary particles having an average primary particle size of 10 to 500 nm, preferably of 50 to 450 nm, even more preferably of 150 to 350 nm.

[0076] Depending upon additional ingredients, the composition can be suitable itself for coating or can be further formulated to yielding proper coating composition.

[0077] The composition of the invention can additionally comprise at least one

(meth)acrylic polymer [polymer (M)].

[0078] Polymer (M) typically comprises recurring units selected from the group of formulae j, jj, jjj:

(j)

(jj)

(jjj)

wherein R4, R5, R6, R7, equal to or different from each other are independently H or C-i-20 alkyl group, RQ is H, alkyl, cycloalkyl, alkaryl, aryl, heterocyclic C-i-36 group. Optionally polymer (M) can comprise additional recurring units different from I, j, jj, jjj, typically derived from ethylenically unsaturated monomers, such as notably olefins, preferably ethylene, propylene, 1 -butene, styrene monomers, such as styrene, alpha-methyl-styrene and the like.

[0079] Preferably, polymer (M) is a polymer comprising recurring units derived from one or more than one alkyl (meth)acrylate. A polymer (M) which gave particularly good result within the context of the present invention is a copolymer of methyl methacrylate and ethyl acrylate. This polymer (M) is notably commercially available under trade name PARALOID™ B-44.

[0080] The composition can also comprise, either in addition to polymer (M) or in alternative to polymer (M), one or more thermoset resin, said thermoset resin can advantageously undergo crosslinking with the grafted copolymer of polymer (F) and comonomer (A).

[0081] Non limitative examples of thermoset resins which can be advantageously used in the composition of the invention are notably:

- melamine resins;

- copolymers containing carboxylic acids functionalities, which, in combinations with carbodiimides (R-N=C=N-R') and grafted copolymers comprising carboxylic groups yield, generally in the presence of amines, thermosetting materials containing N-acyl ureas groups;

- polyesters with carboxylic or hydroxyl or amino functionalities, yielding by reaction with suitable functional grafted copolymer thermosetting polyamides;

- polyamides with amino end groups which can be crosslinked with grafted copolymers containing epoxy groups to form thermosetting

polyamide/epoxide coatings.

[0082] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0083] The invention will be now described in more detail with reference to the following non limitative examples.

[0084] Example 1 - Manufacture of a graft copolymer of P(VDF-co-CTFE) and 2-hydroxyethyl methacrylate

[0085] 5.0 g of a powder of a P(VDF-co-CTFE) polymer (corresponding to 8.5 mmol of CI) was dispersed in 100ml_ of dimethyl phthalate in a 3-neck round bottom flask equipped with a thermometer and a glass stopcock; 5 g of 2-hydroxyethyl methacrylate (HEMA, 38.3 mmol) were then added into said dispersion. After the addition of CuCI (86mg, 0.87mmol), the dispersion was degassed through 3 cycles of freeze-pump-thaw, then the flask was filled with nitrogen. Separately, 267 mg of

4,4'-dimethyl-2,2'-bipyridine (BPy, 1 .71 mmol) were dissolved in 5ml_ of dimethyl phthalate in a flask that was degassed and filled with nitrogen. The solution was transferred into the reaction flask using a syringe. The mixture was heated at 120°C, and all reagents dissolved/swelled upon reaching 90°C forming a bright green solution. After 22 hours, the polymerization was stopped by cooling to room temperature and exposure to air. The grafted polymer separated from the solvent collecting at the bottom of the flask. The polymer was transferred to a separatory funnel and washed 4 times with 500ml_ of 50:50 (v/v) Dl watenmethanol, 500 ml_ of 25:75 (v/v) Dl water: methanol, 500 ml_ of methanol, and 500 ml_ of Dl water.

[0086] During the final wash the polymer was recovered by filtration, and dried at ambient temperature overnight. The grafted polymer P(\/DF-co-CTFE)-g -HEMA was recovered as a free flowing powder.

[0087] Figure 1 is a sketch comprising ⁹F-NMR traces recorded from a

d6-acetone solution of (a) native P(VDF-co-CTFE) polymer and (b) PiVDF-coCTFEJ-^HEMA, obtained as explained herein above; signals in the region around -170 ppm are consistent with a CF group (originally derived from CTFE) having two -CH2- units in alpha position (from VDF and from acrylic monomer).

[0088] Figure 2 is a 2D-NMR spectrum by FH-HOESY, which confirms that the CF group having signals in the -170 ppm region indeed interact both with -CH3 group of HEMA and -CH2- groups of the adjacent VDF recurring unit and HEMA.

[0089] Example 2 - Crosslinking of the P(VDF-coCTFE)-£-HEMA copolymer of example 1 with melamine

[0090] 5 g of the P(VDF-coCTFE)-^HEMA copolymer of example 1 were

solubilised in the minimum required amount of acetone and mixed with 56 mg of melamine resin.

The so-obtained solution was cast onto a glass plate and oven-cured at 120°C for 30 minutes. Upon cooling, a self-standing film was gently detached from the glass support. Said film was tested for its solvent resistance by contacting the same with acetone; no significant swelling nor weight gain or loss was observed when contacting the sample with acetone for 24 hours and separating the same from liquid phase. Thus, grafted and melamine crosslinked materials exhibit increased resistance towards acetone, well known as a good solvent for PVDF polymers.

Claims

1. A method for manufacturing a dispersions of a grafted copolymer, said method comprising:

2. The method of claim 1 , wherein the polymer (F) is a polymer comprising :

(b') optionally from 0.1 to 15%, preferably from 0.1 to 12%, more preferably from 0.1 to 10% by moles of a fluorinated monomer different from VDF; said fluorinated monomer being preferably selected in the group consisting of vinylfluoride (VF-|), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixtures therefrom; and

3. The method of claim 2, wherein polymer (F) comprises recurring units derived from chlorotrifluoroethylene (CTFE).

4. The method of anyone of the preceding claims, wherein comonomer (A) is selected from the group consisting of styrene monomers, (meth)acrylic monomers, chlorinated monomers, functional fluoromonomers.

5. The method of claim 4, wherein comonomer (A) is a (meth)acrylic monomer of formula:

wherein:

each of R'i , R'2, R'3, equal to or different from each other, is independently a hydrogen atom or a C1-C3 hydrocarbon group, and R'4 is a hydrogen atom or a C1-C3 hydrocarbon group, optionally comprising one or more functional groups selected from -OH, -N(R'5)3, wherein each of R'5, equal to or different from at each occurrence, is independently a hydrogen atom or a C1 -C6 hydrocarbon group, an epoxy group, an isocyanate group, a carboxylic group (in its acid, ester or amide form).

6. The method of claim 5, wherein the comonomer (A) is a hydrophilic

(meth)acrylic monomer (MA) of formula:

wherein each of R1 , R2, R3, equal to or different from each other, is

independently a hydrogen atom or a C1-C3 hydrocarbon group, and ROH is a hydrogen or a C1 -C5 hydrocarbon moiety comprising at least one hydroxyl group.

7. The method of anyone of claims 1 to 6, wherein the transition metal is Copper or Ruthenium.

8. The method of anyone of claims 1 to 7, wherein said latent solvent is selected from the group consisting of methyl isobutyl ketone, n-butyl acetate, cyclohexanone, diacetone alcohol, diisobutyl ketone, ethyl acetoacetate, triethyl phosphate, propylene carbonate, triacetin (also known as

1 ,3-diacetyloxypropan-2-yl acetate), dimethyl phthalate, glycol ethers based on ethylene glycol, diethylene glycol and propylene glycol, and glycol ether acetates based on ethylene glycol, diethylene glycol and propylene glycol.

9. A composition comprising particles of at least one grafted copolymer of one vinylidene fluoride (VDF) polymer [polymer (F)] and an ethylenically unsaturated comonomer [comonomer (A)] in a liquid medium comprising at least one latent solvent, said particles being agglomerates of primary particles having an average primary particle size of 10 to 500 nm.