WO2015170030A1 - Sheet comprising a fluorinated polymer, the hydrophilic property of which varies according to the ph - Google Patents

Abstract

The invention relates to a sheet of the type having a matrix comprising a fluorinated polymer and at least one polymer bound to said matrix, of the type selected from the block copolymers produced from a first polymer, called an anchoring polymer, which can bind to said matrix, and a second polymer, the hydrophilic property of which varies according to the pH of the medium containing said sheet. According to the invention, said anchoring polymer is selected from methyl polymethacrylate, copolymers of styrene and methyl polymethacrylate, and polypropylene glycol.

Description

 SHEET COMPRISING A FLUORINATED POLYMER AND

 HAVING A VARIABLE HYDROPHILY BASED ON PH

The present invention relates to a sheet of the type comprising a fluoropolymer matrix and a polymer fixed on said matrix and conferring on the sheet a variable hydrophilicity as a function of the pH of the medium in which the sheet is located.

 The present invention also relates to a sheet of the type comprising a fluoropolymer matrix and a polymer fixed on said matrix and conferring on said sheet a variable wettability with respect to a given fluid as a function of the pH of the external medium and / or the temperature of the leaf.

 The membranes are, for the most part, formed of a porous matrix composed essentially of polymer (s). Fluoropolymer membranes such as polyvinylidene fluoride (PVDF) membranes are used for the filtration of fluids, in particular liquids such as water or biological fluids.

 Depending on the nature of the fluid to be filtered, the membrane must have a hydrophilic or hydrophobic character to optimize filtration.

 It is known to modify the hydrophilic or hydrophobic character of a fluoropolymer membrane.

 Thus, the article "Surface self-assembled zwitterionization of poly (vinylidene fluoride) microfiltration membranes via hydrophobic-driven coating for improved blood compatibility" published in Journal of Membrane Science 454 (2014) (pages 253-263) describes a membrane microporous PVDF on which a particular copolymer has been adsorbed. This particular copolymer is a block copolymer formed of a hydrophobic block obtained from propylene oxide and a hydrophilic block of sulfobetaine methacrylate. The membrane comprising the above-mentioned adsorbed copolymer has a greater hydrophilicity than the same PVDF membrane without adsorbed copolymer.

Similarly, the article "Easy Surface Modification of PVDF Microfiltration Membrane by Strong Physical Adsorption of Amphiphilic Copolymers" published in the journal Journal of Applied Polymer Science in 2013 (pages 31-123121) discloses a PVDF membrane on which a P (PEGMA-r-MMA) copolymer has been adsorbed. This copolymer is a random polymer of poly (ethylene glycol) methacrylate (PEGMA) and poly (methyl methacrylate) (PMMA). The membrane obtained has an increased hydrophilicity compared to a PVDF membrane not comprising the abovementioned copolymer.

 Moreover, there are membranes which are entirely formed of a copolymer having a sensitive pH portion which is capable of modifying the hydrophilicity of the membrane. Thus, the article entitled "Synthesis and Characterization of Poly (Vinylidene Fluoride) with Grafted Acid / Base Polymer Side Chains" published in the journal Macromolecules in 2002, pages 9653-9656, the article entitled "Functionnal and Surface-Active Membranes from Poly (vinylidene fluoride) -graft-Poly (acrylic acid) Prepared via RAFT-Mediated Graft Copolymerization "published in 2004 in the journal Langmmuir, pages 6032 to 6040 as well as the article entitled" Synthesis and Characterization of Poly (acrylic acid) - graft-poly (vinylidene fluoride) Copolymers and pH-Sensitive Membranes "published in 2002 in the journal Macromolecules, pages 673-679 describe such membranes.

 As stated in the publication "Synthesis and Characterization of Poly (vinylidene fluoride) with Grafted Acid / Base Polymer Side Chains" above, the manufacture of the membrane from a copolymer is intended to avoid the clogging of the pores which risk to appear during the grafting of the functional polymer (sensitive pH or sensitive temperature) on the membrane.

Thus, the article "Swellin-induced mesoporous block copolymer membranes with intrinsically active surfaces for size-selective separation" published in Revue Journal of Chemistry in 2012, pages 20542-20548 and documents CN 103120903 A and CN 102764600 A describe methods process for the operation of a film or membranes optionally comprising a fluoropolymer according to which a pH-sensitive copolymer film is formed on the surface of the film or of the membrane, the grafting of the functional polymer is carried out using a copolymer which can be a block copolymer comprising poly (methyl methacrylate) or polystyrene These methods are not simple to implement and do not allow graft functional polymers, including sensitive pH throughout the membrane but only on one of its upper and lower surfaces.

 An object of the present invention is to provide a sheet which comprises a polymer fixed in particular on its surface and which confers on it a wettability, in particular a modified hydrophilicity, with respect to the same sheet without this same fixed polymer, vis-à-vis a given fluid.

 Another object of the present invention is to provide a sheet of fluoropolymer whose hydrophilicity can be modified or modulated depending on the fluid with which it is in contact.

 Another object of the present invention is to provide a sheet as mentioned above which has properties as mentioned above which are stable over time.

 Another object of the present invention is to provide a porous sheet or membrane which has on its surface and / or on the surface of its pores, that is to say in its porous structure, the aforementioned polymer, the latter allowing to give it a given wettability, in particular a given hydrophilicity, especially as a function of the pH of the medium in which the sheet or the membrane is located.

 The present invention relates to a sheet of the type comprising a matrix comprising a fluoropolymer and at least one polymer fixed to said matrix of the type chosen from block copolymers obtained from a first polymer called anchoring polymer which is capable of fix on said matrix and a second polymer whose hydrophilicity is variable depending on the pH of the medium in which said sheet is. According to the invention, typically, said anchoring polymer is chosen from polymethyl methacrylate, copolymers of styrene and polymethyl methacrylate and polypropylene glycol.

 The sheet may be porous and in particular microporous and thus forms a membrane.

 Said fluoropolymer may be chosen from polyvinyl fluoride

(PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyethylenechlorotrifluoroethylene (ECTFE), Nafion and polymers obtained from at least one monomer selected from perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), perfluoropolyether (PFPE) and perfluoropolyoxethane.

 Said second polymer whose hydrophilicity is variable according to the pH of said fluid can be obtained from at least one monomer having a protonated acid form and a non-protonated form which each give said second polymer a different hydrophilicity.

 The second polymer whose hydrophilicity is variable according to the pH can be chosen from:

 the polymers obtained from at least one monomer chosen from

4-vinyl pyridine, acrylic acid (AAc), methacrylic acid (MAAc), maleic anhydride (MA), N, N-dimethylaminoethyl methacrylate (DMAEMA);

 poly (iminoethylene) (PEI), poly (amido amine) dendrimers (PAMAM), poly (N, N-dimethylaminoethyl methacrylate) (PDMAEMA), poly (L-lysine) (PLL), modified chitosan polyanionic polymers and poly (L-histidine).

 The second polymer may be, for example, a homopolymer of 4-vinyl pyridine, a homopolymer of acrylic acid or a copolymer of acrylic acid and 4-vinylpyridine.

When it is a porous or microporous membrane as mentioned above, it may comprise said fixed polymer in its porous structure. It is indeed the merit of the Applicants to have found that the polymer fixed even in the pores of the membrane does not interfere with the filtration properties of the membrane. In addition, a membrane which has in its internal structure, that is to say in its pores, the polymer that gives it the desired property is more reliable than a membrane having this polymer on its surface; indeed, if the surface of the membrane is damaged or worn, it may lose its properties if the polymer is fixed on its surface. A membrane that contains the polymer in its structure is more reliable over time, requires less monitoring and is less frequently renewed. The present invention also relates to a method for treating a substrate containing a fluoropolymer according to which

 a first polymer, said anchoring polymer, is formed capable of being fixed on said substrate;

 copolymerizing said anchoring polymer with at least one monomer which is in two forms, a protonated form and a non-protonated form;

 the block copolymer thus obtained is solubilized in a suitable solvent;

 the copolymer solution is applied to said substrate; and

 said solvent is evaporated,

 According to the invention, said anchoring polymer is chosen from poly (methyl methacrylate), copolymers of styrene and poly (methyl methacrylate) and polypropylene glycol and said monomer has a lower critical solution temperature. The aforementioned monomer may be chosen in particular from the examples given with reference to the sheet of the present invention. It may be in particular a sensitive pH monomer.

 When the substrate is a porous membrane, the copolymer solution can be allowed to penetrate the pores of said membrane prior to evaporating said solvent. A membrane is thus obtained which comprises the polymer fixed in its structure, in particular at the level of the surface of the pores, which open, directly or not, at the level of the surface of the membrane.

The polymers, copolymers and monomers are advantageously as mentioned above with reference to the sheet according to the invention. The suitable solvent used to attach the copolymer to the substrate may be chloroform. The substrate may be an optionally porous sheet, comprising a matrix comprising a fluoropolymer, in particular PVDF or essentially consisting of PVDF. Polymers which have, according to the pH of their medium and / or their temperature, different properties are known. In particular, polymers are known which, as a function of pH or as a function of temperature, have a different hydrophilicity. Thus, the publication "Thermo- and pH-responsive polymers in drug delivery" published in 2006 in the journal Sciencedirect (pages 1655 to 1670) describes various polymers that are said to be thermosensitive or thermo-stimulable because they exhibit a variable hydrophilicity as a function of the temperature of the medium. aqueous in which they are or pH sensitive (pH stimulable) because they have a variable hydrophilicity depending on the pH of the aqueous medium in which they are. These polymers are used for the delivery of pharmaceutical compounds but have never been attached to membranes comprising a fluoropolymer matrix.

 According to one embodiment of the invention, said fixed polymer is, depending on the pH and / or the temperature in a hydrophilic form or in a hydrophobic form.

 The second polymer may be, for example, a homopolymer of 4-vinyl pyridine, a homopolymer of acrylic acid or a copolymer of acrylic acid and 4-vinylpyridine.

 According to another aspect, the present invention relates to a sheet of the type comprising a matrix comprising a fluoropolymer and at least one polymer fixed to said matrix and conferring on said sheet a given wettability with respect to a given fluid. According to this other aspect, the fixed polymer is as a function of the temperature of said sheet, in a form that interacts with said fluid or in a form that does not interact with said fluid, whereby the wettability of said sheet by said fluid is different depending on the shape in which the fixed polymer is located.

 According to this other aspect of the invention, said second polymer has, as a function of the temperature of said sheet / of said fluid, a retracted shape or an extended shape which each give said sheet a different hydrophilicity.

 Thus, said second polymer may be chosen from the following polymers:

 the polymers obtained from at least one monomer chosen from:

the monomers of general formula (I) and (II) below: H ^ H C == €

in which n is an integer greater than or equal to 1 and less than or equal to 12;

 polymers obtained from at least one monomer chosen from N-isopropylacrylamide, Ν, Ν-diethylacrylamide, methylvinylether and

N-vinylcaprolactam;

 copolymers obtained from acrylamide (AAm) and acrylic acid, poly (ethylene oxide) -block-poly (ethylene oxide) block copolymers, poly (oxide of poly) block copolymers; ethylene) block-poly (ethylene oxide) block-poly (ethylene oxide), polyethylene glycol (copolymers of lactic acid and glycolic acid) - polyethylene glycol block copolymers;

 poly (N-alkyl acrylamides, poly (methyl vinyl ether), poly (N-vinyl caprolactams), poly (N-ethyl oxazoline) s, copolymers of acrylic acid and acrylamide, and

 oligo and polypeptides.

According to the invention, the sheet may comprise a single fixed polymer which, depending on the pH of the medium in which the sheet is located, gives it a wettability, in particular a different hydrophilicity as a function of temperature; according to the invention, the sheet may also comprise a single polymer attached to its surface and which gives it a wettability, particularly a different hydrophilicity depending on the pH of the medium in which the sheet is located; according to the invention, the sheet may also comprise at least one polymer which alone confers a wettability variable depending on the temperature and the pH of the medium in which the sheet is. It may be for example, a block copolymer which comprises a thermo-stimulable block and a pH-stimulable block. According to the invention, the sheet may also comprise, fixed on its surface, at least one thermosensitive polymer and at least one sensitive pH polymer which thus allow to modulate the wettability of the sheet, in particular the hydrophilicity of the sheet, according to the two parameters of temperature and pH.

 According to a particular embodiment, said second polymer is obtained by polymerization of a monomer mixture of general formula (I) and a monomer of general formula (II) and in particular by polymerization of a monomer of general formula ( I) in which n = 2 and a monomer of general formula (II) in which n = 9.

 Advantageously, said anchoring polymer is chosen from polymethyl methacrylate, copolymers of styrene and polymethyl methacrylate and polypropylene glycol.

 The present invention also relates to a block copolymer comprising a first block formed of a copolymer of styrene and polymethyl methacrylate and a second block formed of a 4-vinyl pyridine polymer and / or an acrylic acid polymer and / or a copolymer of 4-vinyl pyridine and acrylic acid.

 The present invention also relates to a block copolymer comprising a first block formed of a copolymer of styrene and polymethyl methacrylate and a second block formed of a copolymer of di-ethylene glycol ethyl ether acrylate and nona-ethylene glycol methyl ether acrylate.

DEFINITIONS

 The term "wettability" with respect to a given liquid refers to the ability of the given liquid to form drops on the surface of a flat sheet of a given material. The wettability is evaluated by measuring the contact angle of a drop formed by the given liquid on the sheet of the given material. The higher the contact angle, the lower the wettability of the material by the given liquid.

The contact angle is defined as the angle formed by, on the one hand, the tangent to the drop at the point of contact between the drop and the surface of the sheet of given material and, on the other hand, the surface of the leaf itself The term "hydrophilicity" refers to the ability of a material to be wet or not wet with water. Hydrophilicity is measured by measuring the contact angle of a drop of water formed on the surface of a sheet of the material to be studied.

 The term "matrix comprising a fluoropolymer" refers to a three-dimensional structure formed of a fluorinated polymer or formed of a mixture, in particular of polymers and comprising at least one fluorinated polymer.

 For the purposes of the present invention, the term "polymer" refers to homopolymers, random copolymers, alternating copolymers, block copolymers and branched copolymers. The term "copolymer" encompasses the polymers as mentioned above obtained from at least two monomers or at least one monomer and at least one copolymer or polymer. The copolymers according to the invention may also be terpolymers or copolymers obtained from more than three different monomers and / or copolymers.

 With regard to the fluoropolymer, this denotes any polymer having in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

As an example of a monomer, mention may be made of vinyl fluoride; vinylidene fluoride (VDF, CH ₂ = CF ₂ ); trifluoroethylene (VF ₃ ); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ = CFOCF ₂ CF ₂ SO ₂ F; the product of formula F (CF ₂ ) _n CH ₂ OCF = CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ₁ CH ₂ OCF = CF ₂ in which R ₁ is hydrogen where F (CF ₂ ) z and z is 1, 2, 3 or 4; the product of formula R ₃ OCF = CH ₂ in which R ₃ is F (CF ₂ ) _Z - and z is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene. The fluoropolymer may be a homopolymer or a copolymer, it may also include non-fluorinated monomers such as ethylene or propylene.

 The term "fixed" does not limit the nature and intensity of the forces involved to co-operate the polymer and the surface of the sheet. Thus the polymer can be joined by chemical bonding with the molecules of the surface of the material constituting the sheet; it can be joined because of mechanical interactions, a part of the polymer being blocked in the structure of the surface of the sheet; the polymer can also be attached via Van der Waals forces-type electrostatic interactions. The term "fixed" also refers to any combination of two or more of the above-mentioned types of bond.

 The term "block copolymer" refers to any polymer having at least two blocks, each block being formed of a different polymer obtained, for example, from a particular monomer or mixture of monomers. Each block may be a homopolymer or an optionally block or random copolymer.

 For the purposes of the present invention, the term "stimulable polymer" denotes any polymer that confers on the sheet according to the invention a different wettability depending on the form in which said polymer is located, said form depending on at least one parameter of the invention. medium such as pH and / or temperature. This term encompasses polymers that occur in at least two distinct forms and therefore give the sheet at least two different wettability values. The wettability of the sheet imparted by the polymer does not evolve continuously as a function of revolution of the parameter considered medium.

The term "lower critical solution temperature" (LCST or desolvation temperature) refers to the temperature below which all components of the monomer mixture are miscible. The term "stable over time" means that the variable character of the wettability of the sheet as a function of at least one parameter chosen from the pH and the temperature of the medium is preserved at least one day, advantageously at least one week, in at least one month and more particularly three months.

 The present invention, its features and the various advantages that it provides will appear better on reading the description and examples which follow, given by way of non-limiting examples and with reference to the appended figures in which:

FIG. 1 represents the ¹ H NMR spectrum of the anchoring polymer P1

(P (styrene-stat-MMA)), the solvent used for the ¹ H NMR being deuterated chloroform (CDCl ₃ );

FIG. 2 is the ¹ H NMR spectrum in deuterated chloroform of the P5 copolymer and the chromatograms of the macroinitiator P1 and the P5 copolymer;

FIG. 3 represents the ¹ H NMR spectrum in deuterated chloroform of the P7 copolymer and the chromatograms of the macroinitiator P2 and the P7 copolymer;

FIG. Figure 4 shows the ¹ H NMR spectrum in deuterated chloroform of the P8 copolymer and the chromatograms of the macroinitiator P3 and the P8 copolymer;

 FIG. 5 represents the contact angle of continuous polymer films P4, P5 and P6, respectively, as a function of pH;

 FIG. 6 represents the contact angle of continuous polymer films P7 as a function of the pH;

 FIG. 7 represents the image obtained using a scanning electron microscope of a virgin hydrophilic PVDF membrane (left) and that obtained after deposition of a copolymer whose second block is obtained by polymerization of 4-vinyl pyridine (right);

FIG. 8 represents the contact angle of a hydrophobic PVDF membrane on which the polymer P4 is attached (adsorbed), respectively before pH treatment (left), after treatment with a buffer solution pH = 1 (in the center) and after a second treatment with a buffer solution of pH = 10 (right);

 FIG. 9 shows the measurement of the contact angle of a drop of water on a sheet formed by depositing a P4 polymer film on a molten PVDF film, according to different pH treatments.

EXAMPLES

Synthesis and characterization of block copolymers

The synthesis of the block copolymers is carried out in two distinct stages respectively corresponding to the synthesis of the first block called anchor block, then the second block which is the block which will confer on the membrane a particular hydrophilicity. The first step is carried out in bulk (without solvent) while the second step is obtained in solution because the monomer alone does not allow the solubilization of the macro-initiator. The protocol for obtaining the copolymers and their characterization are detailed below.

EXAMPLE 1 Synthesis of the Anchor Block (Statistical Copolymer) PfS-stat-MMA)

The anchor block consists of PMMA (polymethylmethacrylate), a polymer compatible with PVDF. However, the NMP (controlled radical polymerization by nitroxides) allows a good control of the polymerization of methyl methacrylate (MMA) in the presence of a comonomer such as styrene or acrylonitrile. In the present case, styrene was used at a level of 10 mol% of the total number of styrene / methyl methacrylate moles of the mixture.

The protocol is as follows. In a flask are successively introduced the free SG1 (SG1 = N-tert-butyl-N- [1-diethylphosphono- (2,2-dimethylpropyl)] nitroxide) (against radical), BlocBuilder © (hereinafter referred to as MAMA, marketed by Arkema and corresponding to the following formula:

which is the initiator and the monomers MMA and styrene (purified on inhibitor remover®). After complete solubilization of the initiator, the reaction system is degassed by bubbling nitrogen for 20 min. In order to avoid the possible evaporation of monomer, the balloon is immersed in an ice bath during this step. Then, the thermal energy required for the polymerization is provided by an oil bath (90 ° C) while stirring is provided by magnetic means. The experimental conditions for syntheses of polymers P1, P2 and P3 are listed in the following Table I. Each anchoring copolymer is purified by a succession of three precipitation cycles in a large excess of ethanol (10 times) and vacuum drying (40 ° C.), which makes it possible to remove the residual monomer.

Table I

a DPn = ([S]o+[MMA]₀) / [MAMA]₀. ^b r = 100 x [SG1 ]₀/[MAMA]₀.

a DPn = ([S] o + [MMA] ₀ ) / [MAMA] ₀ . ^b r = 100 x [SG1] ₀ / [MAMA] ₀ .

An example of characterization is given for the polymer P1.

Fig. 1 represents the ¹ H NMR spectrum in deuterated chloroform of a sample taken at the end of the synthesis, which makes it possible to determine the conversion of each monomer. The conversion to MMA can be determined using the characteristic signals of the methoxyl protons of the monomer (3.75ppm) and the polymer (between 2.8 and 3.7 ppm). It should be noted that, depending on the nature of the close neighbors of the MMA, the shielding of the protons concerned varies, which gives rise to the presence of three peaks characteristic of PMMA methoxyl protons. Thus, in FIG. 1, the conversion to MMA is 55.76%. The characteristic spectral zone of the aromatic protons of styrene coinciding with the peak characteristic of chloroform, the conversion to styrene is determined taking into account the experimental conditions and more particularly the rate of styrene introduced relative to the MMA. This makes it possible to determine an integral value corresponding to the totality of styrene present at time t (polymer and monomer) and to compare it with the vinyl proton signal of the monomer (5.25 ppm). Thus, in FIG. 1, the conversion to styrene is 75.94%.

These data lead to a theoretical molar mass Mn _th = M _MAMA +

The ¹ H NMR spectrum of the purified copolymer makes it possible to determine the molar composition of each unit in the copolymer. Thus, the copolymer P1 has 16 mol% of styrene units and 84 mol% of MMA units. By combining this result with the number average molecular weight obtained by size exclusion chromatography (CES) in DMF / LiCl (PMMA calibration), Mn (exp) = 39200 gmol-1, the composition of the first block can be determined by solving the equation system involving the following equations: Mn _eX p = MMAMA + DP _S x M _s + DPMMA XM _M MA and = in

DP _S x where xi represents the mole fraction of i. Thus, the P1 copolymer has 62 styrene units and 326 MMA units.

The chemical properties of each polymer are listed in the following Table II. Table II

a déterminé par RMN¹H.

was determined by ¹ H NMR

b · »·,, CsxMo _v CMMA * [MMA] ₀

Mn _th = M _MAMA + - - x M _s H x M _MMA .

zn MAMA [MAMA] ₀ [MAMA] ₀ ^{M MA}

 c Determined by CES in DMF + LiCI with a PMMA calibration.

d Obtained by solving the system of equations: Mn _exp = MMAMA + DP _S x M _S + DPMMA X MMMA and ^DPMMA = ^ M where X represents the molar fraction of i.

DP _S XS

Synthesis of the block copolymer whose hydrophilicity is variable and function of pH and / or temperature: stimulable block copolymer

 The copolymer whose hydrophilicity can be modified is obtained by rebooting the anchor block and copolymerization with a monomer whose hydrophilicity can be modified or a mixture of monomers having a lower critical temperature. For this, it is necessary to solubilize the anchoring polymer in the reaction system; however the amount of monomer to be introduced for the second step does not allow its total solubilization. In order to overcome this constraint, the polymerization is therefore carried out in solution. Different monomers have been polymerized to obtain copolymers sweeping a wide range of properties.

The pH sensitivity is achieved by copolymers based on 4VP, AA. A second block obtained by a statistical distribution of DEGEA and PEGA makes it possible to obtain a second copolymer which is a statistical P copolymer (DEGEA-stat-PEGA) whose hydrophilic / hydrophobic transition depends on the molar composition of the DEGEA copolymer. The copolymer contains a molar percentage of variable DEGEA, substantially equal to or greater than 0% and substantially equal to or less than 100%; this variable molar content of DEGEA in the copolymer makes it possible to obtain a range of desolvation temperatures (or LCST); each copolymer has, according to its molar content of DEGEA, a desolvation temperature of its own. In the present case, all the desolvation temperatures that can be obtained by varying the molar content of DEGEA are substantially equal to or greater than 15 ° C and substantially equal to or less than 90 ° C. When the copolymer is brought to a temperature substantially equal to its desolvation temperature, its hydrophilicity is modified. As explained below, the monomers making it possible to obtain a second stimulable polymer may enter the composition of a copolymer by reinitiating a first block P (S-stat-MMA).

The following abbreviations correspond to the following compounds:

 4VP AA DEGEA PEGA Whatever the second desired block, the protocol is as follows. The SG1, the macro-initiator, the monomer (s) and the solvent are introduced into a flask. After complete solubilization of the macro-initiator, the reaction system is degassed by bubbling nitrogen for 20 min. In order to avoid the possible evaporation of monomer, the balloon is immersed in an ice bath during this step. Then, the thermal energy required for the polymerization is provided by an oil bath while stirring is provided by magnetic means.

Synthesis of stimulable block copolymers

EXAMPLE 2 Synthesis of Diblock Copolymer with Second Polymer P4VP: Stimulant pH Block Copolymer The handling conditions are such that [4VP] / [macro-initiator P1] = 525 with an excess of free SG1 of 10%. The synthesis is carried out in DMF (36 w%) at 115 ° C. In order to obtain three different block copolymer compositions, the protocol is applied with three different handling times resulting in different conversions. The conversion is calculated using the ¹ H NMR spectrum shown in FIG. 3 (P5 copolymer) by comparison of the characteristic signals of the aromatic protons at alpha of the amine (between 8.1 and 8.6 ppm) of the polymer and the monomer and the vinyl protons of the monomer (5.45 ppm). The characteristic values of the various copolymers obtained are listed in the following Table III. In addition, the molar composition can be determined by comparing the integral of the PMMA methoxylic peak (86% of the total PMMA) and the aromatic alpha protons of the amine of the P4VP block. Thus, the three block copolymers whose synthesis time of the second block is 2.5 hours, 4 hours and 6 hours respectively have polymerization degrees at 4VP of 106, 237 and 301. The volume fraction is obtained by applying the following relation:

 M (4VP)

m (Ρ νΡΛ - ^{Xpwp X} 4VPj ^»

^Xp * ^{vp X} (4VPJ ^{+ XPS X} ÏS) ^{+ XPMMA X} piMMA) where x is the molar fraction, M is the molar mass and p is the density. In addition, the quality of the reinforcement is verified by CES (Chromic exclusion chromatography) in DMF / LiCl through the absence of shoulder of the chromatogram of the copolymer. This technique also makes it possible to determine the polymolecularity index of the copolymer.

Table III copolymer Time C _4V p (%) _Mnth ^b Mn _exp ^c PDI ^C DP

(h) (g.mol ¹ ) (g.mol ¹ ) (4VP) ^a (P4VP) ^d

P4 2.5 19.6 50 200 48 300 1.29 106 0.22

P5 4 39.9 61 900 54 200 1.25 237 0.38

P6 6 53.9 70 700 63 200 1.20 301 0.44 ^was determined by ¹ H NMR.

Mn _th = M _P1 + --- x M _4VP .

c Determined by CES in DMF calibration PMMA.

d calculated according to equation 1.

EXAMPLE 3 Synthesis of the diblock copolymer with AA block: stimulable pH block copolymer

The recrystallization of acrylic acid by NMP on the P block (MMA-stat-S) was carried out in 1,4-dioxane. However, the strong transfer to the solvent during this synthesis does not make it possible to obtain molar masses for the second block greater than 7000 g / mol (1 100 units) while keeping the control of the reaction. Targeting larger molar masses would result in the presence of PAA homopolymer. Thus, AA is primed from P2 (12000 g mol-1) in order to target a molar mass in AA sufficiently low to maintain control. The handling conditions are such that [AA] / [macroinitiator P2] = 280 with a free SG1 excess of 20%. The synthesis is carried out in DMSO (71 w%) at 120 ° C. The conversion to AA is calculated by ¹ H NMR in deuterated DMSO (see Fig. 4) by comparing the characteristic peak of the acid proton present on the monomer and the polymer and characteristic peaks of the vinyl protons of the monomer. Thus, a conversion of 22% is obtained, which corresponds to a DP _n in AA of 62 units. The quality of the reinforcement is checked by CES in THF after having taken care of methylating the AA units. This results in a final copolymer (P7) whose polymolecularity index is 1, 52 having a PAA volume fraction of 0.26.

EXAMPLE 4 Synthesis of the di-block copolymer with a second block PEGA / DEGEA: thermostimulable block copolymer

The reboot of the thermostimulable block is made from P3. PEGA and DEGEA have desolvation temperatures (or lower critical solution temperatures, also known as LCSTs). "Low critical solution temperature") of 80 and 18 ° C in water. The LCST of the PEGA DEGEA block can be modulated by the level of each of the monomers in the block. For this application, an LCST of about 35-40 ° C is desired, which is why the sensitive block is composed of 20% PEGA and 80% DEGEA. The handling conditions for obtaining P8 are such that [Monomers] / [macro-initiator P1] = 126 with a free SG1 excess of 20%. The synthesis is carried out in DMF (60 w%) at 115 ° C. for 20h30. Only the overall conversion can be determined by 1 H NMR (FIG. 5) by comparison of the monomer (3H vinyl) specific signals and the characteristic alpha proton proton of the ester present on the monomers and the polymer. Thus, a global conversion of 66.1 1% is obtained, which corresponds to a DP _n of 83 units. It has already been shown in the laboratory that the initial monomer composition was identical to the composition in the copolymer, which means that the second block consists of 17 PEGA units and 66 DEGEA units. In addition, the CES in DMF / LiCI makes it possible to confirm the reintroduction and to determine the polymolecularity index equal to 1.27.

EXAMPLE 5 Study of the Properties of the Copolymers Obtained

 PH sensitivity study

 a) block copolymer whose second block is obtained by polymerization of VPP

In order to verify the pH sensitivity of the abovementioned copolymers, continuous films are made on a microscope glass slide. Different buffer solution baths are prepared in order to immerse the films therein and thus apply a wide pH range (from 1 to 10) to the copolymer. After drying, the films are dried and the surface properties are measured by contact angle between the surface and a drop of water at pH = 7. Thus, a contact angle profile as a function of pH can be plotted and connected to a protonation state variation of P4VP. Indeed, when the aminated repeating unit is subjected to a pH greater than its pKa (about 5.2 in solution), it is in a deprotonated form which is more hydrophobic than the protonated form (acid form). With reference to FIG. 6, it can be seen that for each of the copolymers P4, P5 and P6 which comprise a second block obtained by polymerization of P4VP, the curve representing the contact angle as a function of the pH systematically has a point of inflection at the level of the pKa marking the separation between the zone where the protonated form is predominant and that where the deprotonated form dominates. b) block copolymer whose second block is obtained by polymerization of AA

 Fig. 6 represents the contact angle of continuous polymer films P7 as a function of the pH. The polymer P7 comprises a second block obtained by polymerization of AA; this copolymer has a PAA volume fraction of 0.26. As can be seen in FIG. 6, there is also a point of inflection of the curve of the contact angle around the pKa.

In the case of this copolymer, the PAA being a polyacid, the predominant form at a pH below the pKa is the protonated form which is therefore more hydrophobic than the deprotonated form (pH> pKa). However, the most hydrophobic form retains a high affinity with water since the contact angle is only 45 °.

Temperature sensitivity study

It is not possible to do the same kind of study (on a temperature scale) from the thermo-stimulable copolymer because its sensitivity is related to the presence of water. Indeed, the change of hydrophilic / hydrophobic state is due to a change of conformation of the chain. Below the LCST (or lower critical solution temperature), the water / polymer interactions are favored which results in a good solubility of the chains which are then extended. On the other hand, when the temperature is higher than the LCST, the polymer / polymer interactions are favored and the polymer curls up on itself to form a hydrophobic domain. The chains are then collapsed. Dry, this phenomenon does not exist. However, the change in behavior could be verified in the case of homopolymers of PEGA DEGEA solubilized in water that following the temperature are soluble (100% transmittance) or not soluble (cloudy solution). The results obtained are not shown here.

EXAMPLE 6 Study of the anchoring of the diblock polymer in the PVDF membrane

The anchoring of the copolymer within the membrane is made possible by the combination of the chemical compatibility between the PMMA and the PVDF and the choice of the solvent used for the insertion of the copolymer. Indeed, the ability of the latter to penetrate the filtration channels (good affinity with PVDF) and locally (extreme channel surface) to swell without solubilizing, in order not to compromise the filtration network of the fluoropolymer, are crucial factors for the anchoring of the copolymer throughout the membrane. Thus, the chosen solvent meeting these conditions is chloroform (good copolymer solvent).

Insertion of the copolymer into the membrane

The copolymer solution is deposited on the membrane and the good affinity with the PVDF allows the penetration thereof into the entire empty volume (channels). Thus, after evaporation of the solvent, the copolymer is distributed homogeneously in the membrane. As can be seen in FIG. 7, scanning electron microscopy does not show any change in the appearance of the membrane after insertion of the copolymer, which confirms that the copolymer penetrates the membrane and does not remain only at the surface. However, the change in wettability properties of the membrane confirms the presence in sufficient quantity of the copolymer within the membrane. The most convincing case is obtained for the deposition of the copolymer on a hydrophilic PVDF membrane. As shown in FIG. 7, a drop of water deposited to make the contact angle measurement immediately penetrates into a PVDF membrane having a porosity of 0.22μηη and having no adsorbed copolymer (right image). On the left side of FIG. 7, it is found on the contrary that the water forms a drop on the surface of the same membrane comprising the copolymer P4 according to the invention adsorbed on its surface. These results have also been verified on both sides of the membrane, which confirms the fact that The copolymer dissolved in chloroform penetrated the membrane after its simple deposition on the latter; this confirms that the copolymer is well distributed throughout the structure of the membrane.

EXAMPLE 7: Study of the pH sensitivity of the membrane

The sensitivity of the membrane according to the invention was verified on a hydrophobic PVDF membrane impregnated with a P4 copolymer solution in chloroform. The membrane thus treated thus comprises the fixed P4 copolymer (adsorbed) on its surface. The application on the membrane according to the invention of a buffer solution affecting the protonation of P4VP contained in the P4 copolymer allows the alternation between the hydrophilic form and the hydrophobic form of the P4 copolymer. PH treatment is then carried out by permeation through the membrane of the invention of a buffer solution at the determined pH for 20 minutes. The membrane is then dried before measuring the contact angle. The results obtained are visible in FIG. 8. As shown in FIG. 8, before treatment by permeation (pH treatment), the membrane according to the invention is hydrophobic and the contact angle is 95 °. After treatment by permeation with a buffer solution of pH = 1 (center photo), the membrane is more hydrophilic because the contact angle is then 39 °. When the same membrane already subjected to permeation with a buffer solution of pH = 1 is subjected to a permeation treatment with a buffer solution at pH = 10, it can be seen, as can be seen in FIG. 8 (left part), that the membrane becomes more hydrophobic, the angle of contact increases and is equal to 75 °.

EXAMPLE 8 Study of the anchoring of the block copolymer

In order to verify the durability of the presence of the copolymer in the membrane, it is subjected to a flow of buffer solution of pH = 1 for 10 days at a rate of 8 hours / day. These conditions are considered extreme because at this pH the P4VP is protonated and therefore hydrophilic, which would cause the copolymer in the flow in the case where it would not be properly fixed. The test is carried out on a membrane of initially hydrophilic PVDF, so the possible desorption of the copolymer can be visualized if one observes an immediate absorption of the drop of water deposited for the measurement of angle of contact. The opposite case (stabilization of the drop) proves that the copolymer is still present on the membrane. The membrane is dried and the contact angle is measured. The results, not shown in detail here, showed that after 8 days of the aforementioned treatment, the copolymer is always present on / in the membrane according to the invention.

 Moreover, in order to better understand the binding of the copolymer to the surface of the membrane, a continuous film is used. For this, a PVDF membrane was melted using a heating press (190 ° C) and thus a continuous and translucent film of PVDF is obtained. The copolymer in solution in chloroform is then deposited on the surface of this film. Logically, the film being continuous and therefore non-porous, the copolymer can not penetrate within the PVDF film. After drying, the copolymer is therefore present on the surface of the PVDF film.

 In order to verify the cooperation between the PVDF and the anchoring block of the copolymer, a PVDF film is used on which a solution of copolymer P4 in chloroform has been deposited. The P4 copolymer is a stimulable pH copolymer based on P4VP. First, it is verified that the hydrophilicity of the P4 copolymer deposited on the PVDF continuous film is variable as a function of the pH. To do this, this film is immersed in a buffer solution at pH = 1; the measurement of the contact angle is equal to 15 °. The same film is then immersed in a buffer solution of pH = 12; the measurement of the contact angle after this second immersion is equal to 67. Then, the film is immersed again in a buffer solution of pH = 1 and stirred for a week. The measurement of the contact angle is then again equal to 15 °. The same results for the measurement of the contact angle are obtained after immersion for 3 months in each of the abovementioned buffer solutions, which makes it possible to verify that the copolymer P4 has a stable behavior over time with respect to the variation. its hydrophilicity as a function of the pH of the solution with which it is in contact.

In order to verify the importance of the anchoring block P (S-MMA) in the fixing of the polymer on the membrane, the same protocol as mentioned above is applied to a continuous film of PVDF on which a homopolymer of P4VP has been deposited. After the first immersion in the buffer at pH1, the measured contact angle corresponds to the contact angle of the PVDF (about 90 °), which means that the P4VP homopolymer is no longer present on the PVDF film. This is explained by the fact that the protonated P4VP is soluble in water at acidic pH; the homopolymer was dissolved in the buffer solution at pH = 1.

Fig. 9 shows the measurement of the contact angle of a drop of water deposited, respectively, on a film obtained by depositing P4 copolymer (P (MMA--stat S ^{62 326)} o, 78-b- (P4VP ¹⁰⁶ ) ₀ , 22) on a continuous PVDF film and on a continuous PVDF film on which a homopolymer of P4VP has been deposited as previously explained. The films are immersed in a buffer solution of pH = 1. After 10 minutes, 1 week and 3 months respectively, each of the films was immersed in a buffer solution of pH = 10 and then the contact angle was measured before immersing the films again in a buffer solution of pH = 1. . Before measuring the contact angle, each film is oven dried at 60 ° C at atmospheric pressure for 30 minutes. Fig. 9 shows that after 10 minutes of immersion in the buffer solution at pH = 1, the measurement of the contact angle corresponds to the contact angle of a drop of water on PVDF: the homopolymer is dissolved in the buffer solution and is no longer present on the film. On the other hand, for the PVDF film coated with the P4 copolymer, the measurement of the contact angle varies as a function of the pH of the buffer solution in which the film is immersed and this even after 3 months, which proves the good fixation. of the block polymer on the surface of the film, the stability of the fixation over time and the stability over time of the behavior of the polymer as a function of the pH of the solution with which it is in contact. A control sample consisting of only one PVDF film was also immersed for one week in a buffer solution of pH = 1; the value of the measurement of the contact angle of a drop of water on the surface of this film before and after immersion does not vary (about 90 ° C).

The above results confirm that washing does not cause desorption of the copolymer despite stringent conditions. This test confirms the anchoring of the polymer within the PVDF. EXAMPLE 9 Study of the anchoring of the copolymer whose hydrophilicity varies with temperature

 The thermostimulable copolymer obtained with reference to example 4 above was also deposited on the molten PVDF. In this case, the presence of PEG acrylate renders the surface hydrophilic. After immersing the whole in water with stirring for a week, the surface is always hydrophilic, which reflects the fact that the copolymer is still present on the PVDF. This result is similar to that obtained with the stimulable pH copolymer.

Claims

Claims:  1. Sheet of the type comprising a matrix comprising a fluoropolymer and at least one polymer fixed to said matrix of the type chosen from block copolymers obtained from a first so-called anchor polymer which is capable of being fixed on said matrix and a second polymer whose hydrophilicity is variable as a function of the pH of the medium in which said sheet is located, characterized in that said anchoring polymer is chosen from polymethyl methacrylate, copolymers of styrene and of polymethyl methacrylate and polypropylene glycol. 2. Sheet according to claim 1, characterized in that it is porous and in particular microporous and thus forms a membrane. 3. Sheet according to any one of the preceding claims, characterized in that said fluoropolymer is chosen from polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyethylenechlorotrifluoroethylene (ECTFE), Nafion and polymers obtained from at least one monomer selected from perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), perfluoropolyether (PFPE) and perfluoropolyoxethane. 4. Sheet according to any one of the preceding claims, characterized in that said second polymer whose hydrophilicity is variable as a function of the pH is chosen from:  the polymers obtained from at least one monomer chosen from 4-vinyl pyridine, acrylic acid (AAc), methacrylic acid (MAAc), maleic anhydride (MA) and N, N methacrylate; dimethylaminoethyl (DMAEMA);  poly (iminoethylene) (PEI), poly (amido amine) dendrimers (PAMAM), poly (N, N-dimethylaminoethyl methacrylate) (PDMAEMA), poly (L-lysine) (PLL), modified chitosan polyanionic polymers and poly (L-histidine). 5. Sheet according to any one of claims 2 to 4, characterized in that it comprises said polymer fixed in its porous structure. 6. Process for treating a substrate containing a fluoropolymer according to which  a first polymer, said anchoring polymer, is formed capable of being fixed on said substrate;  copolymerizing said anchoring polymer with at least one monomer which is in two forms, a protonated form and a non-protonated form;  the block copolymer thus obtained is solubilized in a suitable solvent;  the copolymer solution is applied to said substrate; and  said solvent is evaporated, characterized in that said anchoring polymer is selected from poly (methyl methacrylate), copolymers of styrene and poly (methyl methacrylate) and polypropylene glycol and that said monomer has a lower critical solution temperature.  7. Method according to claim 6, characterized in that the substrate being a porous membrane, the copolymer solution is allowed to penetrate into the pores of said membrane before evaporating said solvent.  8. Process according to claim 6 or 7, characterized in that said solvent is chloroform.