EP2331636A2

EP2331636A2 - Thermoplastic polymer systems modified by copolymers with functionalised blocks

Info

Publication number: EP2331636A2
Application number: EP09756157A
Authority: EP
Inventors: Jean-Pierre Disson; Thomas Fine
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2008-10-02
Filing date: 2009-10-02
Publication date: 2011-06-15
Also published as: KR20110074562A; WO2010037983A2; FR2936805B1; WO2010037983A3; FR2936805A1; US20110245422A1

Abstract

The present invention relates to thermoplastic polymers modified by copolymers that contain acrylic blocks and are functionalised using hydrophilic monomers. The invention relates to a polymer mixture that includes, as a host polymer, a thermoplastic material containing flexible polyether or polyester segments, and at least one copolymer with acrylic blocks dispersed in said host polymer and miscible with the latter, said block copolymer including at least one hydrophilic monomer. The thermoplastic materials modified according to the invention maintain very good transparency properties and further acquire new properties, in particular mechanical properties such as improved mechanical resistance in the molten state during transformation operations characteristic of thermoplastic materials such as extrusion, blowing or calendering operations.

Description

MODIFIED THERMOPLASTIC POLYMER SYSTEMS USING FUNCTIONALIZED BLOCK COPOLYMERS

The present invention generally relates to thermoplastic polymers modified with acrylic block copolymers functionalized with hydrophilic monomers.

A definition of Block Copolymer is given by the International Union of Pure and Applied Chemistry (IUPAC) {Pure Appl. Chem., Vol. 68, No.12, pp. 2287-2311, 1996). In the context of the present invention, a block copolymer is defined as a macromolecule consisting of at least two segments linked by covalent chemical bonds, each segment possibly being a copolymer or a homopolymer according to the IUPAC definitions, and where each segment has at least one different characteristic of the adjacent segment. As known block copolymers, mention may be made of styrene copolymers of the polystyrene-polyisoprene, polystyrene-polyisoprene-polystyrene, polystyrene-polybutadiene, polystyrene-polybutadiene-polystyrene type and the hydrogenated forms of these latter polymers. There are also block copolymers in which some blocks are themselves random copolymers, for example grades of block copolymers containing reactive maleic anhydride comonomers in one of the two blocks.

The development of anionic polymerization and controlled radical polymerization enabled, in the early 1990s, the synthesis of acrylic block copolymers, for example diblocks of the polymethyl methacrylate-butyl polyacrylate (PMM Ap ABu), polymethacrylate type. methyl - polybutadiene, or triblocks of polymethyl methacrylate - butyl polyacrylate - polymethyl methacrylate, polystyrene - polybutadiene - polymethyl methacrylate type. The first block copolymers comprising combinations of acrylic monomers and methacrylic monomers are described in patent EP0408429. In comparison with random copolymers, block copolymers make it possible to obtain new morphologies, in particular with organizations in domains of a few nanometers of the different phases constituted by each of the blocks. These organizations are for example described in Macromolecules, Vol. 13, No. 6, 1980, pp. 1602-1617, or in Macromolecules, vol. 39, No. 17, 2006, pp. 5804-5814.

It is also possible to design a block copolymer of which one of the blocks is compatible with a third polymer acting as a matrix. For example, as described in WO 03/062293, a PMMA-p block copolymer ABu-PMM A introduced into a PMMA matrix leads, thanks to the affinity of the PMMA arms of the block polymer with the PMMA matrix, to the fine distribution of flexible pABu domains playing the role of shock enhancer. More particularly, it is a question of using block copolymers comprising hydrophobic monomers to reinforce thermoplastic matrices, in order to obtain resins that are both transparent and resistant to impact. The block copolymers described in this document have a general formula B- (A) n, n being between 2 and 20, B being a flexible polymer block having a glass transition temperature (Tg) of less than 0 ^° C. A being a rigid polymer block of Tg greater than 0 ⁰ C.

The disclosure of this document is however limited to the advantages resulting from the modification of thermoplastic matrices by means of predominantly hydrophobic block copolymers of formula B- (A) n whose block A is of the same nature or compatible with the matrix. Systems have also been described combining thermoplastic matrices containing polyether or polyester segments with acrylic copolymers having hydrophilic groups; however, these acrylic copolymers are not block copolymers. For example in Example 15 of US Application 3,879,943, a copolymer of 90% of dimethylacrylamide and 10% of butyl acrylate is incorporated into a thermoplastic polyurethane, Estane ^® 5702, to improve the absorption properties of 'water. However, the hydrophilic acrylic copolymer does not correspond to a block structure and a fortiori does not contain any hydrophobic block. Indeed, it is obtained simply by conventional radical polymerization, as described in Example 2 of said document: the monomers are introduced into a reactor together with an initiator of azobisisobutyronitrile type. No additive of those known to obtain controlled radical polymerizations is introduced. Under these conditions, the distribution of the monomers in the copolymer corresponds to a statistical organization, depending on the reactivity of each of the monomers. For further details explaining the differences between conventional radical polymerization and controlled radical polymerization, for example, see Chapter 8 of "Handbook of Radical Polymerization", John Wiley & Sons, 2002. It has now been found that Thermoplastic materials with improved mechanical properties can be obtained by modifying a flexible thermoplastic matrix of polyester or polyether type with acrylic block copolymers functionalized with hydrophilic monomers.

Thermoplastic polymers containing flexible segments of polyester or polyether type are found, for example, in copolyamide, copolyester, thermoplastic polyurethane and polyacetal materials. They are used in various applications such as shoe soles, tubes, flexible mechanical parts used in the automobile (bellows, gaskets, gears, belts), applications that subject these materials to conditions of wear, abrasion, mechanical stresses. The improvement of their mechanical properties such as elongation and resistance to breakage, abrasion resistance, is still sought. In addition their hydrophilicity makes the implementation sensitive to the processing conditions and can thus alter the properties of the material.

It is therefore necessary to improve the window of implementation of thermoplastic polymers containing flexible segments of polyester or polyether type by controlling the rheology and the mechanical properties of the polymer in the molten state. Finally, certain applications of thermoplastic polymers containing flexible segments of polyether or polyester type, such as tubes, connectors for medical applications, require not only good mechanical properties but also transparency. There is therefore a need to improve the mechanical properties of thermoplastic materials which contain flexible segments of polyether or polyester type, in general, especially during extrusion, blowing and calendering operations, while maintaining the properties inherent to these materials. such as transparency, surface appearance, adhesion properties, at a level at least equal to that of the unmodified material. It is an object of the present invention to provide novel thermoplastic materials modified by functionalized acrylic block copolymers having improved properties.

According to a first aspect, the subject of the invention is a mixture of polymers, comprising: as a host polymer, a thermoplastic material which contains flexible segments of polyether or polyester type having a Tg of less than 20 ^° C. as measured by differential calorimetry at scavenger (DSC), and at least one acrylic block copolymer, dispersed in and miscible with said host polymer, said block copolymer having at least one hydrophilic monomer.

The invention is particularly directed to host polymers in which the ester or ether function is in the polymer backbone.

In a preferred variant embodiment, the thermoplastic material is an elastomer, the polyether or polyester segments of the host polymer having a Tg of less than 10 ^° C.

According to a second aspect, the invention relates to the use of acrylic block copolymers comprising at least one hydrophilic monomer for reinforcing thermoplastic polymers containing flexible segments of polyether or polyester type. In the present invention, the term "hydrophilic monomers" refers to monomers that can form hydrogen bonds with water and polar solvents; they are molecules that have oxygen or nitrogen atoms in their basic structure (skeleton).

The hydrophilicity of a monomer can also be defined by means of the corresponding homopolymers which are water-soluble or water-dispersible or of which an ionic form of these homopolymers is.

A homopolymer is said to be water-soluble if it forms a clear solution when it is in solution at 5% by weight in water at 25 ° C.

A homopolymer is said to be water-dispersible if, at 5% by weight in water and at 25 ° C., it forms a stable suspension of fine, generally spherical particles. The average particle size constituting said dispersion is less than 1 mm, and more generally, varies between 5 and 400 nm, preferably from 10 to 250 nm. These particle sizes are measured by light scattering.

The hydrophilicity of a monomer can be further assessed by the logarithmic value of the octanol-1 / water apparent partition coefficient, also called log P or logKow; it can be considered that a monomer is hydrophilic when this value is less than or equal to 2, for example between -8 and 2. The log P values are known and are determined according to a standard test which determines the concentration of the monomer in the water. octanol and in water.

By "hydrophobic monomer" is meant a monomer molecule that repels water, that is, that is insoluble in water and therefore can not create hydrogen bonds with water molecules. Their basic structure is composed of atoms of hydrogen and carbon.

DETAILED DESCRIPTION The applicant has found that functionalizing acrylic block copolymers with various hydrophilic monomers greatly facilitates the miscibility of these copolymers with thermoplastic polymer materials containing flexible segments of polyether or polyester type. These thermoplastic materials have inherent properties such as resistance to abrasion, good mechanical properties at high temperature, a pleasant touch ("soft touch"). The thermoplastic materials modified according to the invention maintain very good transparency properties (which testify to the good miscibility between the resin and the block copolymers), and in addition acquire new properties, especially mechanical ones, such as a better mechanical strength. the molten state during processing operations specific to thermoplastic materials, such as extrusion, blowing or calendering operations.

According to a first aspect, the invention relates to a polymer blend, comprising: as host polymer, a thermoplastic material which contains flexible segments, of polyether or polyester type, having a Tg of less than 20 ^° C. as measured by differential scanning calorimetry (DSC) and at least one acrylic block copolymer dispersed in said host polymer and miscible therewith, said block copolymer comprising at least one hydrophilic monomer. Host Polymer The thermoplastic material forming the host polymer according to the invention contains flexible segments of polyether or polyester type.

In the context of the present invention, the term "flexible segment" is intended to mean any polymer fragment of homogeneous structure whose Tg is less than 20 ^° C., preferably less than 10 ^° C., and more preferentially less than 0 ^° C. The host is preferably chosen from polyester homopolymers, polyether homopolymers, polyacetals, for example polyoxymethylene or copolymers of polyoxymethylene and trioxane, or block copolymers classified in the family of thermoplastic elastomers, such as copolyester esters and copolyesters. ether, polyether block amides, elastomeric polyurethanes (TPU) TPU-ether type, TPU-ester, TPU-polycaprolactone, or polymers where the flexible segment or a part thereof contains thioether functions.

In a preferred embodiment, the thermoplastic material is an elastomer having a Tg of the polyether block or polyester less than 10 ⁰ C.

In the context of the invention, we understand by "thermoplastic material" any polymer-based material having little or no covalent bonds between the polymer chains, and capable of softening under the effect of temperature to be put into operation. works by techniques such as injection, extrusion, extrusion blow molding or calendering.

Preferably, the percentage of flexible segments in the host polymer is 20 to 100%, preferably 40 to 90% by weight. The presence of these soft segments ensures good miscibility with the acrylic block copolymer of the invention as proven inter alia by the excellent transparency qualities presented by the polymer mixtures subject of the invention.

Other properties of the thermoplastic polymers can be improved by the incorporation of acrylic block copolymers functionalized with hydrophilic monomers in these matrices, for example the ability to be printed or varnish, resistance to aging due to exposure to UV radiation, chemical resistance especially to oils and hydrocarbons.

The host polymer has a molecular weight of from 10,000 to 1,000,000 daltons, preferably from 20,000 to 250,000 daltons.

Acrylic block copolymer (s)

This copolymer is chosen from block copolymers ABC and AB in which: each block is connected to the other by means of a covalent bond or of an intermediate molecule connected to one of the blocks by a covalent bond and to another block by another covalent bond,

at least one of the monomers is derived from a derivative of acrylic or methacrylic acid, block A is a homopolymer of a hydrophilic monomer or a copolymer of several hydrophilic monomers, or a copolymer of at least one hydrophilic monomer and of at least one hydrophobic acrylic or methacrylic monomer, block C is a homopolymer or a copolymer of (meth) acrylic or styrenic monomers. It may contain one or more hydrophobic monomers and / or one or more hydrophilic monomers, - block B is incompatible with block A and the optional block C; its glass transition temperature Tg is less than 20 ^° C.

More branched structures are however possible for the acrylic block copolymer, without departing from the scope of the invention.

Preferably, the block copolymer is such that the block B is incompatible with the (s) block (s) side A and C, that is to say they have a parameter of interaction of Flory-Huggins% _AB greater than 0 at room temperature. This results in phase microseparation (observable by scanning electron microscopy), with the formation of a di-phasic structure on a macroscopic scale. The phase separation results in the formation of domains comprising segments from block B and domains comprising segments from block A and / or block C, the size of these areas ranging from a few nanometers to a few tens of nanometers. Block A is a homopolymer of a hydrophilic monomer or a copolymer of several hydrophilic monomers, or a copolymer of at least one hydrophilic monomer and at least one hydrophobic acrylic or methacrylic monomer. Block A may also contain a styrenic monomer, preferably less than 10% by weight. In the case where the block A is a copolymer of at least one hydrophilic monomer and at least one hydrophobic acrylic or methacrylic monomer, the hydrophobic acrylic or methacrylic monomer (s) are preferentially C1-C8 alkyl methacrylates, and more preferably methyl methacrylate. By way of example of hydrophilic monomer, mention may be made of:

acrylic or methacrylic acid, as well as their anionic forms obtained by total or partial neutralization, the amides derived from these acids, for example dimethyl acrylamide (DMA), acrylamide, N-methyl acrylamide, N-methyl acrylamide, hydroxyethylacrylamide, optionally quaternized 2-aminoethyl amino (meth) acrylates, acrylates or methacrylates, optionally alkoxylated polyoxyalkylene (meth) acrylates, for example polyethylene glycol (meth) acrylates (PEG), (meth) methoxypolyethylene glycol acrylates, polypropylene glycol (meth) acrylates, maleic, itaconic, fumaric, maleic anhydride, hydroxy (meth) acrylates, for example 2-hydroxyethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 4-hydroxybutyl acrylate, vinyl hydrosulfide monomers such as N-vinylpyrrolidone, 4-vinylpyridine. Advantageously, the polyethylene glycol group of polyethylene glycol (meth) acrylates has a mass ranging from 300 g / mol to 10,000 g / mol.

In the case where the block A is a copolymer of at least one hydrophilic monomer and at least one hydrophobic acrylic or methacrylic monomer, the proportion of hydrophilic monomer will be greater than 5% by weight, preferably greater than 10%. Block B is elastomeric and essentially hydrophobic, ie free of hydrophilic monomer, but may contain a small fraction (less than 5% by weight of hydrophilic monomer).

Advantageously, the Tg of B is less than 20 ^° C., preferably less than 10 ^° C., and more preferably less than 0 ^° C.

The monomers used to synthesize the elastomeric B block are (meth) acrylates, preferably (C 1 -C 8) alkyl (meth) acrylates, chosen so that the T g of the copolymer is less than 20 ^° C. as an example of (meth) acrylic monomers of low Tg ethyl acrylate (-24 ⁰ C), butyl acrylate (ABu), (-54 ⁰ C), 2-ethylhexyl acrylate ( -85 ^° C.), hydroxyethyl acrylate (-15 ^° C.), butyl methacrylate (20 ^° C.) and 2-ethylhexyl methacrylate (-10 ^° C.). Butyl acrylate is advantageously used. (Meth) acrylates are different from those of block A to meet the condition of incompatibility between B and A. Block B may also contain a styrenic monomer, preferably less than 10% by weight.

The diblock A-B has a number-average molar mass which may be between 10,000 g / mol and 500,000 g / mol, preferably between 20,000 and 200,000 g / mol. The diblock A-B advantageously consists of a mass fraction at A of between 5 and 95% and preferably between 15 and 85%.

Block C is a homopolymer or a copolymer of (meth) acrylic or styrenic monomers. It may contain one or more hydrophobic monomers and / or one or more hydrophilic monomers

The monomers and optionally comonomers of the block C are chosen from the same family of monomers and optionally comonomers as those described above for the block A, however the presence of the hydrophilic monomer is not mandatory. The two blocks A and C of the triblock ABC may be identical or different. They can be different in their molar mass but consist of the same monomers. If block C contains a hydrophilic monomer, this may be identical or different from the hydrophilic monomer of block A. In a preferred variant of the invention, block C has the same composition and the same molecular mass as block A. The block polymers A, B and C may be manufactured by any polymerization means suitable for obtaining block structures, and in particular by controlled radical polymerization. Controlled radical polymerization is understood to mean a conventional radical polymerization in which a check is made of at least one of the steps chosen from priming, propagation, termination and transfer. As an example of control, the reversible deactivation of growing macroradicals can be mentioned. This reversible deactivation can be caused by the addition of nitroxides in the reaction medium. A persistent radical is for example TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) which captures the macroradicals and generally leads to homopolymers of very narrow polymolecularities, thus conferring a living character to radical polymerization. It is also possible to mention beta-phosphorylated molecules having a hydrogen alpha to the nitroxide function.

The triblock A-B-C has a number-average molar mass which may be between 10,000 g / mol and 500,000 g / mol, preferably between

20,000 and 200,000 g / mol. Advantageously, the triblock ABC has the following compositions expressed in mass fraction, the total being 100%: A + C: between 10 and 80% and preferably between 25 and 70%. B: between 90 and 20% and preferably between 75 and 30%. With regard to the polymer mixture according to the invention, it comprises, by weight, the total making 100%: from 0.5% to 70% of at least one block copolymer; from 30 to 99.5% of host polymer. The mixture is obtained using all the thermoplastic blending techniques known to those skilled in the art, for example by extrusion. The mixture may contain other ingredients than the polymers described above, for example plasticizers, lubricants, thermal or UV stabilizers, antioxidants, other polymers, mineral fillers or reinforcements, dyes, pigments. Examples

Example 1. Solvent Polymer Synthesis

1. The first part of this example illustrates the synthesis of a poly (n-butyl acrylate) polymer intended to constitute one of the blocks of the copolymers described in the context of the invention.

In a polymerization reactor equipped with a variable speed stirring motor, inputs for the introduction of reagents, taps for the introduction of inert gases to expel oxygen, temperature measuring probes, a vapor reflux condensing system, a double jacket for heating / cooling the contents of the reactor through the circulation therein of a heat transfer fluid, is introduced:

"A" g of n-butyl acrylate; and - "a" g of polyfunctional alkoxyamine having the following formula:

(The parameters "A", "a", "B", "C" and "D" cited in Example 1 are explained in Table 1).

After several degassings with nitrogen, the reaction medium is brought to 115 ° C. and this temperature is maintained by thermal regulation for several hours. Samples are taken throughout the reaction in order to: determine the kinetics of gravimetric polymerization (measurement of dry extracts); follow the evolution of the number average molecular weight (Mn) as a function of the conversion of monomer to polymer.

When the 80% conversion is reached, the reaction medium is cooled to 60 ^° C. and the residual n-butyl acrylate is removed by evaporation under vacuum.

2. The second part of this example illustrates the reinforcement of the poly (n-butyl acrylate) prepared above with methyl methacrylate or a mixture of methyl methacrylate and dimethylacrylamide.

At 60 ^° C., "B" g of methyl methacrylate, "C" g of dimethylacrylamide and

"D" of toluene is added to the difunctional poly (n-butyl acrylate) prepared in the first part of this example. The reaction medium is then heated at 105 ^° C. for 2 hours and then at 120 ^° C. for another 2 hours. After returning to ambient temperature, the copolymer solution is withdrawn from the reactor and the residual monomers and solvents are removed by evaporation under vacuum.

Table 1 Polymer P1 (according to the invention): The polymer P1 is an ABC triblock where the blocks A and C are identical. Block B is a butyl polyacrylate representing 47% by weight of the ABC block copolymer. Blocks A and C consist of a copolymer obtained from 80% of methyl methacrylate monomer, which is a hydrophobic monomer, and 20% of N, N-dimethylacrylamide monomer, which is hydrophilic. The total number-average molecular weight Mn of the copolymer P1 is 50,000.

For comparison, two other copolymers were used: IEC Polymer (comparative):

The IEC polymer is a triblock ABC where the blocks A and C are identical. Block B is a butyl polyacrylate representing 50% by weight of the ABC block copolymer. Blocks A and C are identical and consist of polymethyl methacrylate (PMMA). It does not contain any hydrophilic monomer. The number-average molecular weight of the IEC polymer is 60,000.

CE2 Polymer (Comparative): The polymer CE2 is a triblock ABC where the blocks A and C are identical. Block B is a butyl polyacrylate representing 50% by weight of the ABC block copolymer. Blocks A and C are identical and consist of polymethyl methacrylate. It does not contain any hydrophilic monomer. The number-average molecular weight of the CE2 polymer is 100,000.

Example 2

The polymers P1, IEC, and CE2 are introduced at a rate of 2% in a Thermoplastic Polyurethane based on an ether-type polydiol (TPU ether) Elastollan ^® 1185 A. The homogenization of the mixture of granules is obtained by recirculation of the material in a micro-DSM extruder. The barrel temperatures are set at 190 ^° C. and the screw speed at 50 rpm. After 5 minutes of re-circulation in the extruder, the material is sent to the extrusion die and the appearance of the rods observed. The unmodified Elastollan® 1185 A leads to a transparent extrudate, as well as that modified with 2% of the triblock copolymer P1. The extrudates using the polymers CE1 and CE2 are highly veiled. This shows a better compatibility between the polymer P1 and the host polymer.

A transmission electron microscopy image after marking microtomed sections with an aqueous solution containing 2% phosphotungstic acid and 2% benzyl alcohol reveals a fine and regular microstructure for the system modified with the polymer P1 (appended FIG. 1). while with CEI and CE2 polymers large nodules, are visible (Figures 2 and 3 appended, respectively). In these shots, the phosphotungstic acid labeling process leads to highlight the rich areas of butyl polyacrylate. More precisely, one can observe that in the case of changing the Elastollan ^® 1185 A by IEC, the nodules have a diameter of about lOOnm or even higher in some cases. In the case of a modification by CE2, one also observes nodules whose size varies between 100 and 400nm. Knowing that the phenomenon of light scattering is noticeable only when the size of the domains becomes close to the wavelength of the visible radiation λ / 4 = 100 nm, it is explained by these microscopy images that the modification by Pl causes a perfectly transparent mixture, in the case of IEC a translucent mixture, and in the case of CE2 a highly veiled mixture. A rheological analysis of the behavior of the mixtures in melt has also been carried out and is illustrated in the appended FIG. 4. These curves show that the addition of 2% of P1 makes it possible to maintain a high viscosity at temperatures in which the TPU alone is difficult to transform. In this sense, the processability window is improved.

Example 3

In a procedure similar to that of Example 1, the polymers described in Table 2 are prepared. The MPEGMA symbol corresponds to methoxypolyethylene glycol methacrylate. The grade used is Bisomer ^® 350MA from COGNIS. The symbol "MAA" corresponds to methacrylic acid, produced by ARKEMA. The DMA symbol corresponds to dimethylacrylamide, available from the company JARCHEM. The "ABu" symbol corresponds to n-butyl acrylate, available from the company ARKEMA. The symbol "MMA" corresponds to methyl methacrylate, also supplied by ARKEMA. The fractions indicated correspond to the mass fraction of each monomer polymerized in the block concerned. The symbol "p" indicates that it is the polymer, the symbol "co" of a copolymer. In the examples of the table, the copolymers are symmetrical and the blocks A and C identical.

Table 2

The acrylic polymers are introduced at a rate of 5% in a thermoplastic polyurethane based on an ether-type polydiol (TPU ether) Estane ^® 58887, or an ester polydiol ester (TPU ester) Estane ^® 58206. The homogenization of the mixture of granules is obtained by re-circulation of the material in a micro-DSM extruder. The barrel temperatures are set at 190 ^° C. and the screw speed at 100 rpm. After 5 minutes of recirculation in the extruder, the material is sent to a mold for obtaining a tensile test specimen. The tensile tests are carried out according to the ISO527 standard, on test pieces corresponding to the IBA geometry defined in this standard.

Observations and results are summarized in Table 3.

++: very good transparency; +: good transparency; 0: translucent product; -: opaque product

Table 3

Claims

A polymer blend, comprising: as a host polymer, a thermoplastic material which contains flexible segments, of polyether or polyester type, having a Tg of less than 20 ^° C. as measured by differential scanning calorimetry (DSC), and at least an acrylic block copolymer dispersed in said host polymer and miscible therewith, said block copolymer comprising at least one hydrophilic monomer.

2. Mixture of polymers according to claim 1 wherein the polyether or polyester segments of the host polymer have a Tg less than 10 ⁰ C, and more preferably less than 0 ⁰ C.

3. Mixture of polymers according to one of claims 1 and 2 wherein the ester or ether function is in the polymer backbone of the host polymer.

4. Mixture of polymers according to one of claims 1 to 3 wherein the percentage of flexible segments in the host polymer is 20 to 100%, preferably 40 to 90%.

5. Mixture of polymers according to one of claims 1 to 4 comprising by weight, the total making 100%: from 0.5% to 70% of at least one block copolymer; from 30 to 99.5% of host polymer.

6. Polymer blend according to one of the preceding claims wherein the host polymer is chosen from: homopolymers polyester, polyether homopolymers, polyacetals such as polyoxymethylene or copolymers of polyoxymethylene and trioxane, or block copolymers classified in the family of thermoplastic elastomers such as copolyesters-esters and copolyesters-ether, polyether block-amides, elastomeric polyurethanes (TPU) TPU-ether type, TPU-ester, TPU-polycaprolactone, or polymers where the flexible segment or a part thereof contains thioether functions.

7. Polymer blend according to one of the preceding claims wherein the molecular weight of the host polymer ranges from 10,000 to 1,000,000 Da, preferably from 20,000 to 250,000 Da.

8. Polymer blend according to one of the preceding claims, in which the acrylic block copolymer is chosen from the ABC and AB block copolymers in which: each block is connected to the other by means of a covalent bond or an intermediate molecule connected to one of the blocks by a covalent bond and to the other block by another covalent bond, at least one of the monomers is derived from a derivative of acrylic or methacrylic acid, block A is a homopolymer of a hydrophilic monomer or a copolymer of several hydrophilic monomers, or a copolymer of at least one hydrophilic monomer and at least one hydrophobic acrylic or methacrylic monomer, - the C block is a homopolymer or a copolymer of monomers

(Meth) acrylic or styrenic, containing one or more hydrophobic monomers and / or one or more hydrophilic monomers, the block B is elastomeric and contains less than 5% by weight of hydrophilic monomer.

9. Mixture of polymers according to claim 8 wherein the block B has a glass transition temperature Tg less than 20 ⁰ C and is incompatible with the block A and the eventual block C, this incompatibility resulting in a micro-separation of domain-level phases with domain formation comprising segments from block B and domains comprising segments from block A and / or block C.

10. Mixture of polymers according to one of claims 8 and 9 wherein the proportion of hydrophilic monomer in the block A is greater than 5% by weight, preferably greater than 10%, when the block A is a copolymer of at least a hydrophilic monomer and at least one hydrophobic acrylic or methacrylic monomer.

11. Polymer blend according to one of the preceding claims wherein the hydrophilic monomer is selected from: acrylic or methacrylic acid, and their anionic forms obtained by total or partial neutralization, the amides derived from these acids such as for example the dimethyl acrylamide

(DMA), acrylamide, N-methyl acrylamide, N-hydroxyethylacrylamide, amino (meth) acrylates, 2-amino ethyl acrylates or methacrylates optionally quaternarized, - optionally alkoxylated polyoxyalkylene (meth) acrylates, by polyethylene glycol (meth) acrylates (meth) acrylates, methoxypolyethylene glycol (meth) acrylates, polypropylene glycol (meth) acrylates, maleic, itaconic, fumaric, maleic anhydride, hydroxy (meth) acrylates, for example 2-hydroxyethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 4-hydroxybutyl acrylate, water-soluble vinyl monomers such as N-vinylpyrrolidone, 4-vinylpyridine.

12. Mixture of polymers according to one of claims 8 to 11 wherein the acrylic block copolymer is an ABC triblock of molar mass average number between 10,000 g / mol and 500,000 g / mol, preferably between 20,000 and 200,000 g / mol, and has the following composition expressed as a mass fraction: A + C: between 10 and 80% and preferably between 25 and 70%; B: between 90 and 20% and preferably between 75 and 30%.

The polymer blend of claim 12 wherein block C has the same composition and molecular weight as block A.

The polymer blend of claim 13 wherein the host polymer is a polyurethane thermoplastic based on an ether type polydiol, and the block copolymer is a triblock whose central block is a butyl polyacrylate and the side blocks are formed. copolymer of methyl methacrylate (MMA) and dimethylacrylamide (DMA).

The polymer blend of claim 14 wherein said side blocks are 80% PMMA and 20% by weight PDMA.

16. Mixture of polymers according to one of claims 8 to 11 wherein the acrylic block copolymer is a diblock AB of number average molar mass between 10,000 g / mol and 500,000 g / mol, preferably between 20 000 and 200 000 g / mol, and consists of a mass fraction at A of between 5 and 95% and preferably between 15 and 85%.

17. Use of acrylic block copolymers comprising at least one hydrophilic monomer for reinforcing thermoplastic polymers containing flexible segments, of polyether or polyester type, having a Tg of less than 20 ^° C. as measured by differential scanning calorimetry (DSC).