MX2007005860A - Acrylic capstock. - Google Patents

Abstract

The invention concerns a multilayer structure comprising successively: a protecting layer (I) comprising a PMMA; optionally a pigmented layer (II); an intermediate ductile layer (III) comprising a sequenced polymer of formula BAn consisting of: a polymer sequence B including at least by weight 60 % of at least one (meth)acrylic monomer having a Tg lower than -5 C, and n polymer sequences A, bound to the polymer sequence B through covalent bonds, n representing an integer between 1 and 10, comprising by weight less than 60 % of at least one (meth)acrylic monomer having a Tg higher than 0 C; a structural plastic layer (III), the layers being arranged on one another in the sequence (I) to (IV) as indicated, and such that if the pigmented layer is not present, the total thickness of the layers (I) and (III) is more than 310 m.

Description

ACRYLIC FOR PACKING CAPS FIELD OF THE INVENTION The present invention relates to a plastic structure protected by an acrylic polymer reinforced for impact with the help of a ductile intermediate layer disposed between the plastic structure and the protective layer BACKGROUND OF THE INVENTION Certain structure plastics such as polystyrene for impact (HIPS), ABS resins (acrylonitrile-butadiene-styrene), PVC are widely used in the manufacture of molded articles that are frequently found in everyday life (caravan or mobile home coverings, window profiles, doors or blinds). mechanical stability and are relatively inexpensive, have a poor resistance to aging (in the broadest sense, ie resistance to light, to scratching, to solvents and chemicals, ...). normal to cover these plastics with a protective layer.

Due to their mechanical properties and their excellent resistance to aging, tearing and chemical products, acrylic polymers are perfectly adapted to protect structural plastics. In addition, once protected, structural plastics also have a better gloss, characteristic of acrylic polymers. The protective layer must adhere perfectly on the plastic to be protected in order to guarantee a good level of protection over time. The plastic protected by the protective layer must also retain its impact resistance. European applications EP 1541339 Al and EP 1543953 A2 both describe a multilayer acrylic film which allows to protect the structure plastics and give them a new appearance. According to one of the forms of the invention, the film comprises an acrylic surface layer (A), a layer (B3) made from a sequenced copolymer and an optional acrylic layer (C). The film is applied in two stages. In a first stage, the film, which can be previously stored in the form of a roll, is preformed to the required geometry, then in a second stage, the thermoplastic in the molten state is injected into a mold and the film is applied on the molten thermoplastic. The use of an acrylic film has disadvantages. Firstly, because of its rigidity, such a film is not manipulated (ie stored in the form of rolls, then unrolled) easily. In addition, the dimensions of the film sold to a transformer are not necessarily adapted to those of the mold, which can generate important waste. Finally, the problem of adhesion of the film on the plastic to be protected can arise. In effect, the film is rigid when it is applied on the molten thermoplastic. In contact with the latter, softens what facilitates contact and adhesion but the softening may not be homogeneous and regular, especially in the presence of a mold with complicated geometry, which implies a heterogeneous adhesion of the film. In the two previously mentioned European applications, the thickness of the film (ie the set of layers (A) / (B3) / optionally (C) is limited to 300 μm, preferably up to 100 μm, in order to guarantee a good easy handling of the film and good adhesion on the plastic by the technique of "Film Inserting Molding" used The applicant has found that it is possible protect a plastic structure with the help of a protective layer that adheres perfectly and that does not harm the impact resistance of plastic structure. The procedure used is simpler and more economical than the process that uses an acrylic film and allows obtaining thicker structures. The Prior Art European application EP 1174465 A1 discloses a multilayer structure comprising a substrate coated with a surface layer composed of an acrylic copolymer, which is preferably a copolymer based on methyl methacrylate (MMA) and butyl methacrylate. European Application EP 1546058 A1 discloses a multilayer structure comprising a substrate coated with a surface layer composed of a center-shell type acrylic copolymer (heart-shell). International Application WO 00/08098 describes a multilayer structure comprising a substrate coated with a surface layer composed of an acrylic copolymer based on MMA and an alkyl acrylate and optionally a core-shell type impact modifier. The International Application WO 2004/087786 describes a monolayer film comprising an acrylic block copolymer. The film is used to coat structural plastics (ABS, PC, PP, PVC, ...). US Pat. No. 4,350,742 discloses a multilayer structure comprising a polystyrene layer and a layer of an acrylic polymer. The adhesion between the layers is reinforced when the polystyrene contains as comonomer an α, β-unsaturated carboxylic acid. US Pat. No. 6,455,171 describes a multilayer structure comprising an acrylic surface layer, an intermediate ductile layer based on a copolymer of an olefin and an acrylate or a sequenced copolymer composed of a conjugated diene and an aromatic monomer of vinyl.

SUMMARY OF THE INVENTION The invention concerns a multilayer structure comprising in the order: • a protective layer (I) comprising a PMMA, • optionally a pigmented layer (II), • an intermediate ductile layer (III) comprising a copolymer sequenced of formula BAn composed: - of a polymer sequence B comprising weight at least 60% of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, and - of n polymeric sequences A, linked to the polymeric sequence B by covalent bonds, n which designates an integer between 1 and 10, comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg greater than 0 ° C. • a layer of structural plastic (III), the layers are arranged one above the other in the order (I) to (IV) indicated, and so that if the pigmented layer was not present, the total thickness of the layers (I ) and (III) is greater than 310 μm. The invention is also related to a method for protecting a structural plastic consisting of a co-extruder in the order: • a protective layer (I) comprising a PMMA, • possibly a pigmented layer (II), • a ductile intermediate layer (III) comprising a block copolymer of Formula BAn comprising: - a polymer sequence B comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, and - of n polymer sequences A, attached to the polymer sequence B by covalent bonds, n denotes an integer comprised between 1 and 10, comprising by weight at least 60% of at least one (meth) acrylic monomer having a Tg greater than 0 ° C, • a layer of structural plastic (III). The invention also concerns the use of a sequenced copolymer of Formula BAn composed of: - a polymer sequence B comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, and - of n polymer sequences A, linked to the polymer sequence B by covalent bonds, n denotes an integer comprised between 1 and 10, comprising at least 60% by weight of at least one (meth) acrylic monomer having a higher Tg at 0 ° C, for the preparation of a ductile intermediate layer (II). The invention may be better understood by reading the detailed description that will follow and non-limiting implementation examples thereof, and the examination of the appended figures.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 represents a multilayer structure 1 comprising three layers with references 2, 3 and 4 arranged one above the other. The layer 2 corresponds to the protective layer (I), the layer 3 to the intermediate ductile layer (II) and the layer (IV) to the structural plastic (IV). Figure 2 represents a multilayer structure 5 comprising 4 layers with references 2, 2 ', 3 and 4 arranged one above the other. The layer 2 corresponds to the protective layer (I), the layer 2 'to the pigmented layer, the layer 3 to the intermediate ductile layer (II) and the layer 4 to the structural plastic (IV). Figure 3 represents a diagram of the measuring device of the elasticity 6. The bar 7 is placed on the supports 8 and 8 '. The hammer 9 applies a force F on the bar 7. A device, not shown, continuously registers force and displacement. Figure 4 represents an AFM atomic force microscope plate of the trisequenced copolymer 3 whose preparation is detailed in the examples section.DETAILED DESCRIPTION OF THE INVENTION Definitions Tg designates the glass transition temperature of a polymer. By extension, it will be designated by Tg of a monomer the Tg of the homopolymer obtained by radical polymerization of said monomer. The term (meth) acrylate denotes, to simplify, an acrylate or a methacrylate. It is designated by (meth) acrylic monomer, a monomer which may be: an acrylic monomer such as acrylic acid or its salts, the alkyl acrylates in C? -C?, Cycloalkyl or aryl such as the acrylate of methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl, hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate, alkyl ether acrylates such as 2-methoxyethyl acrylate , the alkoxy- or aryloxypolyalkylene glycol acrylates such as the methoxypolyethylene glycol or ethoxypolyethylene glycol acrylates, the aminoalkyl acrylates such as 2- (dimethylamino) ethyl acrylate, the silylated acrylates, the glycidyl acrylate, • a methacrylic monomer such as methacrylic acid or its salts, alkyl methacrylates in C 2 -C 6, cycloalkyl or aryl methacrylates such as ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl methacrylates , the hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate, alkyl ether methacrylates such as 2-methoxyethyl methacrylate, alkoxy- or aryloxypolyalkylene glycol methacrylates such as methoxypolyethylene glycol or ethoxypolyethylene glycol methacrylates, aminoalkyl methacrylates such as 2- (dimethylamino) ethyl methacrylate, silylated methacrylates, glycidyl methacrylate. It is designated by PMMA, a homo- or copolymer of MMA, comprising at least 50% by weight of MMA. The copolymer is obtained from the MMA and at least one comonomer copolymerizable with the MMA. Preferably, the copolymer comprises from 70 to 99.5% by weight, advantageously from 80 to 99.5% by weight, preferably from 80 to 99% of MMA for 0.5 to 30%, advantageously from 0.5 to 20%, preferably 1 to 20% comonomer respectively. Preferably, the comonomer is a (meth) acrylic monomer or an aromatic vinyl monomer such as, for example, styrene, substituted styrenes, alpha-methyl styrene, monochlorostyrene, tert-butyl styrene. Preferably, the comonomer is a (meth) acrylate of alkyl. It is preferably methyl, ethyl, propyl, butyl acrylate, butyl methacrylate. The acrylic polymer is prepared by radical polymerization according to techniques known to the person skilled in the art. The polymerization can take place in solution, in bulk, in emulsion or in suspension. The acrylic polymer can also be prepared by means of anionic polymerization. In the case of the protective layer (I), it comprises a PMMA. Preferably, the melt index of the PMMA (measured at 230 ° C, under a load of 3.8 kg) is between 0.5 and 10 g / 10 minutes, advantageously between 1 and 5 g / 10 minutes. The protective layer (I) has the function of protecting the plastic structure against scratches, chemicals and against aging. It also allows to improve the brightness of certain structural plastics. ' For example, ABS has a single brightness of about 40-50 at an angle of 60 °. A brightness between 70 and 95, preferably between 85 and 90 can be obtained via the protective layer (I). Preferably, the PMMA is reinforced for impact with the help of at least one modifier impact. The impact modifier can be an acrylic elastomer such as a styrene-butadiene-methyl methacrylate block copolymer. It can also be presented in the form of thin multi-layer particles, called heart-shell (core-shell), having at least one elastomeric (or soft) layer, ie a layer formed of a polymer having a Tg of less than -5 °. C and at least one rigid (or hard) layer, ie formed of a polymer having a Tg greater than 25 ° C. Preferably, the Tg polymer below -5 ° C is obtained from a mixture of monomers comprising from 50 to 100 parts of at least one C? -C10 alkyl (meth) acrylate, from 0 to 50 parts of a copolymerizable monounsaturated comonomer, from 0 to 5 parts of a copolymerizable crosslinking monomer and from 0 to 5 parts of a copolymerizable graft monomer. Preferably, the Tg polymer above 25 ° C is obtained from a mixture of monomers comprising from 70 to 100 parts of at least one C? -C alkyl (meth) acrylate, from 0 to 30 parts of a copolymerizable monounsaturated monomer, from 0 to 5 parts of a copolymerizable crosslinking monomer and from 0 to 5 parts of a copolymerizable graft monomer. Preferably the Tg polymer above 25 ° C it has a mean molecular mass expressed in weight equivalents of PMMA comprised between 10000 and 1000000, advantageously between 50000 and 500000 g / mol. The d-Cι alkyl (meth) acrylate is preferably butyl, 2-ethylhexyl, octyl acrylate. The C? -C alkyl (meth) acrylate is preferably methyl methacrylate. The copolymerizable monounsaturated monomer can be an Ci-Cio alkyl (meth) acrylate, styrene, alpha-methyl styrene, butyl styrene, acrylonitrile.

It is preferably styrene or ethyl acrylate. The graft monomer may be the allyl (meth) acrylate, the diallyl maleate, the crotyl (meth) acrylate. The crosslinking monomer may be diethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, divinyl benzene, trimethylolpropane triacrylate (TMPTA). The multilayer particles can be of different morphologies. For example, "X-hard-hard" particles having an elastomeric core can be used (inner layer) and a rigid crust (outer layer). The European application EP 1061100 Al describes said particles. Example of "soft-hard" type particles: composed of a soft core (40% by weight) obtained by polymerizing 99 parts of butyl acrylate and 1 part of allyl methacrylate; and - of a hard crust (60% by weight) obtained by polymerizing 95 parts of MMA, 5 parts of butyl acrylate in the presence of 0.002 parts of n-dodecyl mercaptan; - particle size: 145-155 nm. Particles of the "hard-soft-hard" type having a rigid core, an elastomeric intermediate layer and a rigid crust can also be used. US Application 2004/0030046 Al discloses examples of said particles. Example of "hard-soft-hard" type particles: composed: - of a hard core (23% by weight) obtained by polymerizing 92.7 parts of MMA, 10 parts of ethyl acrylate, 0.3 parts of allyl methacrylate; and - of a soft intermediate layer (47% by weight) obtained by polymerizing 81.7 parts of acrylate from butyl, 17 parts of styrene and 1.3 parts of allyl methacrylate; - of a hard crust (30% weight) obtained by polymerizing 96 parts of MMA and 4 parts of ethyl acrylate; - particle size: 157 nm. Particles of the "soft-hard-soft-hard" type can also be used, having, in order, an elastomeric core, a rigid intermediate layer, another elastomeric intermediate layer and a rigid crust. The French Application whose publication number is FR-A-2446296 describes examples of said particles. Example of soft-hard-soft-hard-type particles composed of: - a soft core (4% by weight) obtained by polymerizing 19.1 parts of butyl acrylate, 4.5 parts of styrene, 0.5 parts of allyl methacrylate; and - of a hard layer (25% by weight) obtained by polymerizing 141 parts of MMA, 9 parts of ethyl acrylate and 0.6 parts of allyl methacrylate; - of a soft layer (56% by weight) obtained by polymerizing 266.8 parts of butyl acrylate, 62.5 parts of styrene, 6.7 parts of allyl methacrylate; - of a hard crust (15% by weight) obtained at polymerize 84.6 parts of MMA and 5.4 parts of ethyl acrylate; - particle size: 270 nm. The elastomeric layer may also be of the silicon type as disclosed in US Applications 2005/0124761 Al. The particle size is generally less than μm and advantageously between 50 and 300 nm. The multilayer particles are prepared with the aid of aqueous emulsion polymerization, in several stages. During the first stage, germs are formed around which the layers are to be formed. The final size of the particles is determined by the number of germs that are formed from the first stage. In the course of each of the following steps, by polymerizing the appropriate mixture, a new layer is successively formed around the germs or particles of the preceding step. In each step, the polymerization is conducted in the presence of a radical initiator, a surfactant and optionally a transfer agent. For example, sodium, potassium or ammonium persulfate is used. The particles once formed are recovered by coagulation or by atomization. An anti-caking agent can be added to prevent the particles from agglomerating. The impact modifier ratio in the PMMA ranges from 0 to 60 parts, advantageously from 1 to 60 parts, preferably from 5 to 40 parts, even more preferably from 10 to 25 parts for 100 parts of PMMA. The usable impact modifiers are for example: the DURASTRENGTH® D320 of the company ARKEMA; the IRH 70 of the company MITSUBISHI (soft / hard bilayer with a soft heart of butadiene-butyl acrylate copolymer and a hard shell of PMMA); the KM-355 of the company ROHM and HAAS. By way of examples of usable PMMA, mention may be made of those marketed by the company ARKEMA under the references ALTUGLAS® DRT, ALTUGLAS® MI 7T, ALTUGLAS® HFI 10, ALTUGLAS® MI 4T, ALTUGLAS® MI 2T. ALTUGLAS® V044 or by the company ROEHM GmbH under the references PLEXIGL S® 6N, PLEXIGLÁS® 8N, PLEXIGLÁS® ZK5BR. In the case of the intermediate ductile layer (III), it comprises a block copolymer of formula BAn composed of: - a polymer sequence B comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than - 5 ° C, and - of n polymer sequences A, linked to polymer sequence B by covalent bonds, n denotes an integer comprised between 1 and 10, comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg greater than 0 ° C. In the case of sequence B, it is obtained from a mixture MB comprising at least 60% by weight, advantageously at least 70%, preferably at least 80% of at least one (meth) acrylic monomer having a lower Tg a - 5 ° C. Preferably, the Tg of the (meth) acrylic monomer is less than -15 ° C, still more preferably less than -25 ° C. Preferably, the (meth) acrylic monomer of polymer sequence B is butyl methacrylate, 2-ethylhexyl hexyl or octyl methacrylate. The MB mixture comprises: • from 60% to 100%, advantageously from 70% to 100%, preferably from 80% to 100% of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, for respectively, from 0 to 40%, advantageously from 0 to 30%, preferably from 0 to 20% of at least one comonomer copolymerizable with the (meth) acrylic monomer. Preferably, the copolymerizable comonomer is a (meth) acrylic monomer different from the monomer (met) acrylic of Tg less than - 5 ° C or an aromatic vinyl monomer. The molecular mass by weight of the sequence B is between 40000 g / mol, advantageously between 50000 and 150000 g / mol (expressed in PMMA equivalents). In the case of sequences A, these are obtained from an MA mixture comprising at least 60% by weight, advantageously at least 70%, preferably at least 80% of at least one (meth) acrylic monomer having a higher Tg at 0 ° C. Preferably, the Tg of the (meth) acrylic monomer of the polymer sequences A is greater than 25 ° C, even more preferably greater than 50 ° C. Preferably, the (meth) acrylic monomer of the polymer sequences A is methyl methacrylate. The mixture MA comprises: • from 60% to 100%, advantageously from 70% to 100%, preferably from 80% to 100% of at least one (meth) acrylic monomer having a Tg greater than 0 ° C, respectively • from 0 to 40%, advantageously from 0 to 30%, preferably from 0 to 20% of at least one monomer copolymerizable with the (meth) acrylic monomer. Preferably, the copolymerizable comonomer is a (meth) acrylic monomer different from the monomer (met) acrylic of Tg higher than 0 ° C or an aromatic vinyl monomer. The molecular mass by weight of each of the sequences A is between 10000 and 100000 g / mol, advantageously between 30,000 and 60,000 g / ml (expressed in PMMA equivalents). The sequence B has a Tg lower than -5 ° C, preferably lower than -15 ° C, even more preferably lower than -25 ° C. Sequences A have a Tg higher than 0 ° C, preferably higher than 25 ° C, even more preferably higher than 50 ° C. The person skilled in the art knows how to select the monomers that make up the A and B sequences to regulate his Tg. You can use particularly Fox's Law (for this purpose see: Bulletin of the American Physical Society 1, 3, page 123 (1956)). Preferably, the sequence B and the sequences A will be selected so that they are incompatible, that is to say, they present an interaction parameter of Flory-Huggins XAB >; 0 at room temperature. This implies a phase separation with formation of a diphasic structure on a macroscopic scale. This phenomenon is called phase microseparation. Phases whose size is less than 100 nm are formed, preferably comprised between 10 and 50 nm. The intermediate ductile layer (III) may also comprise a core-shell type impact additive whose proportion varies from 0 to 60 parts, preferably from 0 to 30 parts, to 100 parts of sequenced copolymer. The intermediate ductile layer has the function of reinforcing the impact resistance of the plastic structure / protective layer assembly. In fact, when a protective layer based on PMMA is applied, which is a fragile material, on a plastic structure, the impact resistance of the assembly is lower than that of the plastic structure alone and is substantially equivalent to that of the protective layer . A fissure primed in the PMMA layer propagates unhindered to the plastic structure and damages the latter. In the presence of the intermediate ductile layer, the impact resistance of the assembly is preserved until improved in relation to the plastic structure since, in this case, the crack is stopped by the intermediate ductile layer. The sequenced copolymer BAn According to the definition given by the IUPAC (see IUPAC Compendium of Chemical Terminology, 2nd edition (1997), 1996, 68, 2303), a sequenced copolymer consists of macromolecules having several chemically bonded polymer sequences, ie derived from different monomers or derived from the same monomers but according to different distributions. You can also contact Kirk-Othmer Encyclopedia of Chemical Technology 3a. Ed., Vol. 6, p. 798 for more details on the block copolymers. The copolymer can be linear, star or comb ("brush" copolymer). Preferably the copolymer is a trisequenced copolymer of formula ABA. The sequenced polymers can be prepared by means of a polymerization called live. It may be a group transfer polymerization using a system associating a silylketene and a Lewis acid as described in Japanese Application JP 62-292806. It may also be a controlled radical polymerization technique of the NMP type (Nitroxide-Mediated Polymerization), ATRP (Atomic Transfer Radical Polymerization), or RAFT (Reversible Addition- Fragmentation Chain Transfer, Fragmentation Chain Transfer by Reversible Addition). Information about these techniques will be found in the following publications: D. A.

Shipp et al., "Water-borne block copolymer synthesis and a simple and effective one-pot synthesis of acrylate-methaceylate block copolymers by atom transfer radical polymerization", Am. Chem. Soc., Polym. Prep., 1999, Vol. 40, p. 448; Y. K. Chong et al., "A more versatile route to block copolymers and other polymers of complex architecture by living radical polymerization: the RAFT process," Macromolecules, March 1999, Vol. 32, No. 6, p. 2071-2074; G. Moineau et al., "Synthesis and characterization of poly (methyl methacrylate) -block-poly (n-butyl acrylate) -block-poly (methyl methacrylate) copolymers by two step controlled radical polymerization (ATRP) catalyzed by NiBr2 (PPH3) 2, Macromolecules 1999, Vol. 32, No. 25 pages 8277-8282". It can also be a living anionic polymerization. The living anionic polymerization is primed by an organic compound of an alkaline or alkaline earth metal such as, for example, n-butyl lithium, sec-butyl lithium, 1-diphenyl hexyl lithium or fluorenyl lithium. The control of the polymerization can be improved by associating the primer to an aluminum compound and eventually to a Lewis base such as an ether or an amine. The aluminum compound is preferably a monoaryloxydialkylaluminum or a bis (aryloxy) monoalkyl aluminum such as for example isobutyl bis (2,6-di-t-butyl-4-methylphenoxy) aluminum or diisobutyl (2,6-di-t-butyl-4-methylphenoxy) ) aluminum. The Lewis base is for example selected from the following : dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, anisole; 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-diisopropoxy ethane, 1,2-dibutoxyethane, 1,2-diphenoxy ethane, 1,2-dimethoxypropane, 1,2-diethoxypropane, 1,2-diisopropoxypropane, 1, 2- dibutoxipropane, 1,2-diphenoxypropane, 1,3-dimethoxypropane, 1,3-diethoxypropane, 1,3-diisopropoxypropane, 1,3-dibutoxypropane, 1,3-diphenoxypropane, 1,4-dimethoxybutane, 1, 4- diethoxybutane, 1,4-diisopropoxybutane, 1,4-dibutoxybutane, 1,4-diphenoxybutane, diethylene glycol dimethyl ester, dipropylene glycol dimethyl ether. The following documents illustrate the combination of such a primer with an aluminum compound and optionally with a Lewis base: US 6831144 B2, EP 1348735 A1, US 6878789 B2. Preferably, the combination of sec-BuLi, of isobutyl bis (2,6-di-tert-butyl-4-methyl-phenoxy) aluminum and of 1, 2 is used. dimethoxyethane. An organic compound of an alkali metal or alkaline earth metal may also be associated with an alkali metal or alkaline earth metal alcoholate as set forth in the following documents: EP 0408429 Bl, EP 0524054 Bl and EP 0402219 Bl. Advantageously, the NMP type polymerization is used to prepare the copolymer sequenced in the presence of an alkoxyamine of the formula ZTn, in which Z denotes a multivalent group and T a nitroxide. Z designates a multivalent grouping, that is to say a grouping capable of releasing, after activation, several radical sites. The activation in question is produced by breaking the covalent bonds Z-T. By way of example, Z may be selected from the following groupings (I) to (VIII): (Q wherein R3 and R are identical or different, represent an alkyl radical, linear or branched having a number of carbon atoms ranging from 1 to 10, phenyl or thienyl radicals optionally substituted by a halogen atom such as F, Cl, Br or for a alkyl radical, linear or branched, having a number of carbon atoms ranging from 1 to 4, or even by nitro, alkoxy, aryloxy, carbonyl, carboxy radicals; a benzyl radical, a cycloalkyl radical having a number of carbon atoms ranging from 3 to 12, a radical containing one or more unsaturations; B represents a linear or branched alkyl radical, having a number of carbon atoms ranging from 1 to 20; m is an integer ranging from 1 to 10; R5í "- € V HH CCHHr-0M" -C ^ - ~ taT3 > V) p-rCC-C0K-CaH? 2 »CCaiBrR6 (H) II 11 oo in which R5 and Rβ, identical or different, represent aryl, pyridyl, furyl, thienyl radicals, optionally substituted by such a halogen atom as F, Cl, Br, or by an alkyl radical, linear or branched, having a number of carbon atoms ranging from 1 to 4, or even by nitro, alkoxy, aryloxy, carbonyl, carboxy radicals; D represents a linear or branched alkylene radical, having a number of carbon atoms ranging from 1 to 6, a phenylene radical, a cycloalkylene radical; p being an integer ranging from 1 to 10; wherein R7, R8 and R9, identical or different, have the same meanings as R3 and R of Formula (I), q, r and s are integers ranging from 1 to 10; in which R? 0 has the same meaning as R5 and R6 of the formula (II), t is an integer ranging from 1 to 4, u is an integer between 2 and 6 (the aromatic grouping is substituted); in which Ru has the same meaning as the radical R? 0 of the formula (IV) and v is an integer between 2 and 6; wherein R12, R13 and R14, identical or different, represent a phenyl radical, optionally substituted by a halogen atom such as Cl, Br, or by an alkyl radical, linear or branched, having a number of carbon atoms that goes from 1 to 10; W represents an atom of oxygen, of sulfur, of selenium, W is equal to zero or 1; wherein R15 has the same meaning as R3 of Formula (I), R15 has the same meaning as R5 or Re of Formula (II); wherein R17 and R? 8 identical or different represent a hydrogen atom, an alkyl radical, linear or branched having a number of carbon atoms ranging from 1 to 10, an aryl radical, optionally substituted by a halogen atom or a heteroatom.

T, designates a nitroxide which is a stable free radical having a grouping = N-0 *, ie a grouping on which an electron is present alone. A stable free radical is designated as a radical that is persistent and non-reactive with respect to air and humidity in ambient air, which can be manipulated and preserved for a longer period than most free radicals (for this purpose see , Accounts of Chemical Research 1976, 9, 13-19). The stable free radical is thus distinguished from free radicals whose life span is ephemeral (from a few milliseconds to a few seconds) as the free radicals from the usual primers of polymerization such as peroxides, hydroperoxides or azo primers. Free radical polymerization primers tend to accelerate polymerization when stable free radicals generally tend to make it slower. It can be said that a free radical is stable in the sense of the present invention if it is not a polymerization primer and if, under the usual conditions of the invention, the half-life of the radical is at least one minute. T, is represented by the structure: ugly wherein RX9, R20, R2 ?, R22, R23 and R24 denote groupings: linear or branched C 1 -C 20 alkyls, preferably C 1 -C 20 such as methyl, ethyl, propyl, butyl, isopropyl, isobutyl, tert-butyl , neopentyl, substituted or unsubstituted, substituted or unsubstituted C6-C30 aryl such as benzyl, aryl (phenyl), saturated cyclic C1-C30 and in which the groupings R19 and R22 can be part of a cyclic structure R? g -CNC-R22 optionally substituted that can be selected from: where x denotes an integer between 1 and 12.

By way of examples, the following nitroxides may be used: OXOTEMPO TEMPO Particularly preferably, the nitroxides of Formula (X) are used in the context of the invention: Ra and Rb designate identical or different alkyl groups possessing from 1 to 40 carbon atoms, optionally linked together so as to form a cycle and optionally substituted by hydroxy, alkoxy or amino groups, RL designates a monovalent group of molar mass greater than 16 g / mol, preferably greater than 30 g / mol. The grouping RL can for example have a molar mass between 40 and 450 g / mol. It's about preference of a phosphorus grouping of General Formula (XI): In which X and Y, which may be identical or different, may be selected from the alkyl, cycloalkyl, alkoxyl, aryloxyl, aryl, aralkyloxy, perfluoroalkyl, aralkyl radicals and may comprise from 1 to 20 carbon atoms; x and / or Y may also be a halogen atom such as a chlorine, bromine or fluorine atom. Advantageously, RL is a phosphonate grouping of formula: in which Rc and Rd are two identical or different alkyl groups, optionally linked so as to form a cycle, comprising from 1 to 40 carbon atoms, optionally substituted or not. The RL grouping may also comprise at least one aromatic ring such as the phenyl radical or the naphthyl radical, substituted for example by one or more alkyl radicals comprising from 1 to 10 carbon atoms. carbon. The nitroxides of formula (X) are preferred since they allow a good control of the radical polymerization of the (meth) acrylic monomers as set out in WO 03/062293. The alkoxamines of formula (XIII) having a nitroxide of formula (X) are then preferred: wherein: Z denotes a multivalent grouping; Ra and R designate identical or different alkyl groups having from 1 to 40 carbon atoms, optionally linked together so as to form a cycle and optionally substituted by hydroxy, alkoxy or amino groups; RL designates a monovalent grouping of molar mass greater than 16 g / mol, preferably greater than 30 g / mol.

The grouping Ri can, for example, have a molar mass between 40 and 450 g / mol. It is preferably a phosphorous group of general formula (XI): In which X and Y, which may be identical or different, may be selected from the alkyl, cycloalkyl, alkoxyl, aryloxyl, aryl, aralkyloxy, perfluoroalkyl, aralkyl radicals and may comprise from 1 to 20 carbon atoms; X and / or Y may also be a halogen atom such as a chlorine, bromine or fluorine atom. Advantageously, RL is a phosphonate grouping of formula: in which Rc and Rd are two identical or different alkyl groups, optionally linked so as to form a cycle, comprising from 1 to 40 carbon atoms, optionally substituted or not. The RL grouping can also comprise at least one aromatic ring such as the phenyl radical or the naphthyl radical, substituted for example by one or more alkyl radicals comprising from 1 to 10 carbon atoms.

As an example of nitroxide of formula (X) which can be contained by the alkoxamine (XIII), it can be mentioned: N-tert-butyl-l-phenyl-2-methylpropyl nitroxide; N- (2-hydroxymethylpropyl) -1-phenyl-2-methylpropyl nitroxide; N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide; N-tert-butyl-1-di (2,2,2-trifluoroethyl) phosphono-2-, 2-dimethylpropyl-nitroxide; N-tert-butylbutyl (1-diethylphosphono) -2-methylpropyl] nitroxide; N- (1-methylethyl) -1-cyclohexyl-1- (diethylphosphono) nitroxide; N- (1-phenylbenzyl) - [(1-diethyl phosphono) -1-methylethyl] nitroxide; N-phenyl-1-diethylphosphono-2,2-dimethylpropylnitroxide; N-phenyl-1-diethylphosphono-1-methylethylnitroxide; N- (1- phenyl-2-methylpropyl) -1-diethylphosphonomethylethyl nitroxide; as well as the nitroxide of formula: The nitroxide of formula (XIV) is particularly preferred: It is N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, commonly called SGI for simplicity. This nitroxide allows to effectively control the polymerization of the (meth) acrylic monomers. Alkoxyamines can be prepared by means of recipes described for example in US 590549 or in FR 99.04405. One method that can be used is to perform the coupling of a carbon radical with a nitroxide. The coupling can be carried out from a halogenated derivative in the presence of an organometallic system such as CuX / ligand (X = Cl or Br) according to an ATRA type reaction (Atom Transfer Radical Addition) as described by D. Greszta et al. In Macromolecules 1996, 29, 7661-7670.

-I- n CuX ligand - to CuX2 / ligand The alkoxyamines that can be used in the Framework of the invention are represented below: DIAMINS twenty The alkoxyamine DIAMS is the preferred alkoxyamine. It would not be outside the scope of the present invention to combine several alkoxyamines corresponding to the formula (I), in particular several alkoxyamines of formula (XIII). A process for obtaining the block copolymer BAn comprises the following steps: 1. The sequence B is prepared by heating the MB mixture in the presence of at least one alkoxyamine ZTn, heating being carried out at a temperature sufficient to activate the alkoxyamine and polymerize the mixture MB up to a conversion of at least 60%, 2. Sequences A are prepared by heating the sequence B obtained in step 1 in the presence of the MA mixture, heating being carried out at a temperature sufficient to activate sequence B and polymerize the mix MA. The priming of the polymerization leading to sequence B is carried out by means of the alkoxyamine ZTn.

The priming of the polymerization leading to the sequences A is carried out by means of the reactivation of the sequence B. In order to ensure a better control of the polymerization, a nitroxide, identical or identical, can be added to stage 1 and / or 2. different from the one contained in the alkoxyamine. The molar ratio of the nitroxide added in relation to the alkoxyamine ZTn is between 0 and 20%, preferably between 0 and 10%. The conversion to monomer (s) of the MB mixture in step 1 is between 60 and 100%. Preferably, in order to preserve control of the polymerization, the conversion is between 60 and 95%, advantageously between 70 and 95%. In each of the steps, it can be removed under vacuum, possibly by heating, all or part of the unconverted monomers. It is also possible to finish converting all or part of the non-converted monomers in each step by introducing at least one radical initiator during this step. The radical primer can be introduced in each step before or after the preparation of the corresponding sequence (s). It is possible that the control of the polymerization is not perfect and that the mixture of monomers leading to the sequences A also leads in part to a polymer A of the same composition as the sequences A. A composition comprising from 50 to 100 parts is obtained of ABn sequenced copolymer and from 0 to 100 parts of polymer A having the same composition as the A sequences. This composition can be used also for the intermediate ductile layer. In the case where the radical primer is introduced before the preparation of a sequence (for example, in the case of sequence B, if it is added to the MB mixture and the alkoxyamine ZTn), it will be selected so as not to interfere with the preparation of the sequence. Preferably, the radical initiator is selected so that it has a temperature T 2 / h (ie the temperature to have a half-life of 1 hour) is 20 ° C higher than the activation temperature of the alkoxyamine ZTn or of sequence B. The radical initiator can be an organic or inorganic primer, such as a persulfate. Azobisisobutyronitrile or LUPEROX® 546 are two examples of suitable radical initiators. Each of the stages of the procedure can be conducted according to a mass procedure, in solution in a solvent or aqueous dispersed medium (emulsion, suspension). In the case where it is desired to prepare the copolymer sequenced in dispersed aqueous medium, the two steps can be conducted in dispersed aqueous medium or only stage 2. In that case the sequence B will have been previously prepared to stage 1 according to a mass process or solution in a solvent. An example of a process for the preparation of the sequenced copolymer BAn in aqueous disperse medium in which the sequence B has been previously prepared according to a process in bulk or in solution in a solvent comprises the following steps: a) the water is introduced, at least one dispersing agent, sequence B and mixture Mn, b) the mixture MA is polymerized by heating at a temperature sufficient to activate sequence B, c) the sequenced copolymer BAn is recovered. The dispersing agent is a compound that stabilizes the emulsion or suspension. It can be, for example, a surfactant or a protective colloid. The sequenced copolymer is recovered in the form of particles whose size depends on the operating conditions and the procedure used. (emulsion, suspension). The copolymer is advantageously granulated, for example, with the aid of an extruder. A radical primer can be introduced before and / or at the end of step b). If the radical primer is introduced before step b), it is preferably selected so that it does not interfere with the B sequence in polymerization of the MA mixture. It is preferably selected so that its temperature T? / 2/1 h (that is, the temperature to have an average life time of 1 h) is 20 ° higher than the reactivation temperature of the B sequence. also introduce a transfer agent before and / or at the end of step b). For example, the transfer agent may be octal mercaptan. Additives The intermediate ductile layer (III) and the protective layer (I) can each comprise one or more additives selected from: • thermal stabilizers; • lubricants; • fireproof; • pigments (organic and inorganic); • anti-UV rays; • antioxidants; • antistatic; • opacifying agents which may be mineral fillers such as talc, calcium carbonate, titanium dioxide, zinc oxide, or organic fillers such as, for example, cross-linked beads based on MMA styrene (examples of such beads are given in EP 1174465). The intermediate ductile layer (III) and the protective layer (I) can each comprise at least one anti-UV, The proportion of the anti-UV rays in the intermediate ductile layer (II) or in the protective layer (III) is from 0 to 10 parts, advantageously from 0.2 to 10 parts, preferably from 0.5 to 5 parts, of anti-UV rays per 100 parts of polymer. A list of usable UV-rays will be found in the document "Plastic Additives and Modifiers Handbook, Chapter 16, Environmental Protective Agents," J. Edenbaum Ed., Van Nostrand, pages 208-271, incorporated herein by reference. Preferably, the anti-UV is a compound of the HALS family, triazines, benzotriazoles or benzophenones. Combinations of several anti-UV rays can be used to obtain better resistance to UV rays. As examples of usable UV radiation, mention may be made of TINUVIN® 770, TINUVIN® 328 P or TINUVIN® 234. The intermediate ductile layer (III) and the protective layer (I) may each comprise minus one pigment. The proportion of pigment in the intermediate ductile layer (III) or in the protective layer (I) is 0 to 20 parts, advantageously from 0.2 to 10 parts, preferably from 0.5 to 5 parts, of pigment per 100. parts of polymer. A list of pigments that can be used in the document "Plastics Additives and Modifiers Handbook, Section VIII, Colorants", J. Edbau, Ed., Van Nostrand, pp. 884-954, incorporated herein by reference. As examples of pigments which can be used, mention may be made of titanium dioxide (white), clay (beige), metal particles (metallic effect) or treated mica particles of the IRIODIN® brand marketed by MERCK. In the case of plastic structure, it is selected from the following list of polymers: • saturated polyester (PET, PETg, PBT, ...); • ABS; • SAN (styrene-acrylonitrile copolymer); • ASA (acrylic-styrene-acrylonitrile copolymer marketed in particular by GE PLASTICS under the trademark GELOY®); • polystyrene (glass or impact); • polypropylene (PP); • polyethylene (PE); • polycarbonate (PC); • PPO; • polysulfone; • PVC; • Chlorinated PVC (PVCC); • Expanded PVC. It can also be mixtures of two or more plastics from the preceding list. For example, it can be a PPO / PS or PC / ABS mixture. Multilayer structure The multilayer structure comprises in order: • a protective layer (I) comprising a PMMA, • possibly a pigmented layer (II), • an intermediate ductile layer (III) comprising a block copolymer of formula BAn composed: - of a polymer sequence B comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, and • of n polymeric sequences A, linked to the polymeric sequence B by covalent bonds, n denoting an integer between 1 and 10, comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg greater than 0 ° C. • a layer of structural plastic (III), the layers being arranged one on top of the other in the order (I) to (IV) indicated, and so that if the pigmented layer is not present, the total thickness of layers (I) and (III) is greater than 310 μm, preferably greater than 350 μm. When a so-called depth of color effect is sought, the intermediate ductile layer (III) comprises at least one pigment and the protective layer (I) is transparent and without any pigment. According to a variant, in order to obtain the effect of depth of color, a pigmented layer (II) can be arranged between the protective layer (I) and the intermediate ductile layer (III). The pigmented layer (II) comprises at least one pigment dispersed in a thermoplastic resin which is preferably a PMMA. The proportion of pigment varies from 1 to 50 parts of pigment per 100 parts of acrylic polymer. The protective layer (I) has a thickness comprised between 10 and 500 μm, preferably between 50 and 200 μm. The intermediate ductile layer (III) has a thickness comprised between 100 and 1000 μm, preferably between 100 and 400 μm. The optional pigmented layer (II) has a thickness comprised between 10 and 80 μm, preferably between 10 and 50 μm. In relation to the FIM technology described in the European Applications EP 1541339 Al and EP 1543953 A2, the set of layers (I), (II) and (III) may have a thickness greater than 310 μm. Procedure The multilayer structure can be obtained by hot compression of layers (I) to (IV). It is also possible to use a multi-injection technique consisting of injecting in the same mold the molten materials that constitute the layers. According to a first multi-injection technique, the molten materials are injected into the mold at the same time.

According to a second technique, a movable insert is located in the mold. By this insert, a molten material is injected into the mold, then the movable insert is moved to inject another molten material. The preferred technique is co-extrusion that relies on the use of as many extruders as there are layers to be extruded. This technique is more flexible than the previous ones and allows obtaining multilayer structures also for complicated geometries, for example profiled. It also allows to have an excellent mechanical homogeneity. The co-extrusion technique is a technique known for the transformation of thermoplastics (see, for example, Précis de matiéres plastiques, Structures- proprietés, 1989, mise en oeuvre et normalisation 4a. edition, Nathan, p. 126). US 5318737 descrian example of co-extrusion with a plastic structure. The procedure consists in protecting a structural plastic by superposing in the order by hot co-extrusion or by multi-injection: • a protective layer (I) comprising a PMMA, • possibly a pigmented layer (II), • a ductile intermediate layer ( III) comprising a block copolymer of formula BAn composed of: - a polymer sequence B comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C and - of n sequences polymer A linked to the polymer sequence B by covalent bonds n denoting an integer comprised between 1 and 10, comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg greater than 0 ° C, • a layer of structural plastic (IV). Preferably, the method consists of protecting a structural plastic by co-extruding in the order: • a protective layer (I) containing a PMMA, • optionally a pigmented layer (II), • an intermediate ductile layer (III) comprising a block copolymer of formula BAn composed of: - a polymer sequence B comprising at least 60% by weight of at least one monomer (met) acrylic having a Tg less than -5 ° C, and - of n polymeric sequences A linked to the polymer sequence B by covalent bonds, n denotes an integer comprised between 1 and 10, comprising at least 60% by weight of at least a (meth) acrylic monomer having a Tg greater than 0 ° C, • a layer of structural plastic (IV). Applications The multilayer structure of the invention can be used for the manufacture of objects and articles of everyday life. It can be, for example: • boxes or cases of mowers, cutters, nautical motorcycles, household appliances, ...; • of car roof chests; • body parts; • of mineralogical plates; • exterior wall panels for caravans and mobile homes; • of external panels of refrigerators; • shower cabin panels; • of building doors; • of window moldings; • Walls PVC is used as a plastic structure in the manufacture of parts that are intended for exterior applications such as building doors, channels, window moldings or fences. However, the degradation of PVC under the effect of UV rays implies a change of color (especially in dark colors such as blue or black) and / or a decrease in its resistance to impact. In addition, the panels in PVC usually contain UV stabilizer, titanium dioxide which also plays the role of white pigment. The proportion of titanium dioxide is generally of the order of 3% which makes it difficult to obtain dark colors. The panels can not be colored except in light colors or pastel. The invention solves the problem of coloring and / or protecting the UV rays of the exterior facade panels in PVC, always maintaining the impact resistance of PVC. The invention also has characteristics of an exterior facade panel comprising in the order: • a protective layer (I) containing a PMMA, • possibly a pigmented layer (II), • an intermediate ductile layer (III) comprising a sequenced copolymer of formula BAn composed of: - a polymer sequence B comprising at least 60 % by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, and - of n polymer sequences A, linked to the polymer sequence B by covalent bonds, n denoting an integer between 1 and 10, comprising at least 60% by weight of at least one monomer (met) acrylic that has a Tg higher than 0 ° C. • a layer of PVC (IV); The layers being arranged one above the other in the order (I) to (IV) indicated. Preferably, if the pigmented layer is not present, the total thickness of layers (I) and (III) is greater than 310 μm. ABS is advantageously used as structural plastic in the manufacture of boxes or housings, particularly of household electrical appliances, of mineralogical plates, of external panels of refrigerators or of body parts. The ABS has a brightness on the order of 40-50 at an angle of 60 °. Thanks to the invention, it is possible to obtain a brightness comprised between 70 and 95, preferably between 85 and 90 under an angle of 60 ° while always retaining the impact resistance of the ABS and protecting the ABS. EXAMPLES The following examples illustrate the invention in the best form ("best mode") contemplated by the inventors. They are given for illustrative purposes only and do not limit the scope of the invention. Multilayer structures were obtained by coextrusion, then evaluated with the help of a rapid flexion test. The Izod impact on the notch on certain samples was also measured. Co-extrusion conditions The structures multilayers have been made on a line of coextrusión calandreada tricapa of mark AMUT. A block of distribution of the layers in lamellae has been used to perform the coextrusion as well as a subsidiary blanket holder 650 mm wide. The calendering of the structure was carried out on a vertical calender made up of three independently thermoregulated rollers. The ABS is extruded at a temperature between 245 and 255 ° C with the help of a 70 mm diameter machine, of length equal to 32D provided with a degassing well. The extruder used for the layer of the trisequence copolymer has a diameter of 30 mm and a length of 24 D, the temperature is regulated to approximately 250 ° C. The surface PMMA is when extruded with an extruder 30 mm in diameter and 25 D in length at a temperature of approximately 250 ° C as well. Conditions for measuring the impact of Xzod to the ISO 80 notch Test tubes: 80 x 10 mm V-shaped: 8 mm Pendulum: 1 J Speed: 3.46 m / s Rapid bending test The elasticity (Re, resilience) is measured, expressed in kJ / m2, on ABS specimens protected or not by an acrylic protective layer. The elasticity is measured with the help of a rapid bending test. The specimen is subjected to a bending in the middle of the validity range at a constant speed. During this test, the load applied to the specimen is measured. The bending test is performed at constant speed on the servo assembly Hydraulic MTS-831. The force is measured by means of a piezoelectric cell embedded in the nose of the firing pin of the range 569.4 N. The displacement of the specimen during the application is measured by an LVDT sensor on the 50 mm range hydraulic jack. During the trial, force was recorded (expressed in N) and the displacement (in mm) of the striker. From the experimental curves, the area under the curve representing the force as a function of the displacement until the rupture of the specimen or the limit of displacement before sliding is calculated. (evaluated at 20 mm). This area, expressed in Joule, is representative of the energy provided to the system at the time of loading. The resistance to bending, indicated Re is the energy of rupture in relation to the right central section of the bar expressed in kJ / m2. Preparation of the test pieces Bars corresponding to the following dimensions were manufactured with the help of a Charlyrobot CRA numerical milling machine from the multilayer structures. 6 bars were cut per plate.

The specimen dimensions, in millimeters, are: - long: 70 +/- 0.2 - width: b = 10.0 +/- 0.2 - thickness: h = measured for each specimen. The range L, distance between the supports, is regulated to L = 40 mm. The application speed applied is 0.1 m / s. For each sample, the contact face with the hammer is the ABC. The thin layer is requested in traction. Preparation of trisequenced copolymers Three trisequenced copolymers were prepared. The copolymer 1 has been prepared by bulk polymerization while the trisequenced copolymers 2 and 3 have been prepared in suspension in water. Trisequenced copolymer 1 Trisequenced copolymer 1 is prepared by bulk polymerization. 6000 g of butyl acrylate, 35 g of alkoxyamine DIAMS and 1 g of nitroxide SG1 are introduced into a metal reactor provided with mechanical stirring and a double jacket. The temperature of the mixture is brought to 115 ° C. After 225 minutes, the conversion is 60% and the butyl polyacrylate has a number average mass of 66960 g / mol, 128300 g / mol by weight and a polymolecularity index of 1.9. The 5325 g of MMA is then displaced in the reactor. The temperature of the viscous mixture is 90 ° C. A product composed of PMMA- is then obtained b-poly (butyl acrylate) -PMMA. mass average in number: 80110 g / mol average mass by weight: 192900 g / mol polymolecularity: 2.4 molar content of butyl acrylate: 49.5% molar content of methyl methacrylate (MMA): 50.5% Copolymer trisequence 2 First stage: preparation of a solution comprising live butyl polyacrylate in MMA. In a 20 liter reactor stirred at 20 revolutions per minute, polymerized at 117 ° C, 14000 g of butyl acrylate in the presence of 140 g of DIAMINS to a degree of conversion of 70% as measured by dry extraction. Butyl polyacrylate has the following molecular masses in PMMA equivalents: average peak mass: 97220 g / mol average mass in number: 67810 g / mol average weight mass: 106990 g / mol average mass in z: 148020 g / mol polomolecularity: 1.6 12200 g of the preceding mixture are immediately displaced in a shaken 20-liter cuvette at 100 revolutions per minute, then evaporated under vacuum (4 h, 80 ° C, 20 mm Hg), the butyl acrylate not converted to a viscous butyl polyacrylate having a solids degree of about 96%. The butyl polyacrylate is rediluted by adding 10,500 g of MMA. The solution obtained has a solids degree of 45%. It comprises 45% of live butyl polyacrylate (ie reactivable) for 55% MMA. Second stage: preparation of the trisequenced copolymer 2 The copolymer is prepared in suspension in water. The polymer from the polymerization of 2-acrylamido-2-methylpropan sulfonic acid neutralized with sodium hydroxide is used as the dispersing agent. The dispersing agent is prepared according to example 1 of the American Patent US 5733992; has a Brookfield viscosity of 4 Pa.s at 25 ° C. The dispersing agent is designated by PAMS in the continuation of the examples. It is charged to a 20 liter reactor that has been previously degassed and purged with nitrogen, 7000 g of deionized water, 509 g of a 5.3% by weight PAMS solution and 0.37 g of NaOH. The mixture is brought to 70 ° C under an agitation of 200 revolutions per minute. Then 4230 g of the butyl polyacrylate solution are displaced in the MMA prepared in step 1.

The reaction mixture is brought to 100 ° C over a period of 2 hours at the end of which a mixture of 3.7 g of octyl mercaptan diluted in 11.2 g of MMA is introduced. The reaction mixture is left under stirring at 100 ° C for 1 hour. At the end of this period, a mixture of 6.75 g of LUPEROX® 26R and 247 g of MMA is continuously introduced for 1 hour. At the end of this period, a solution of 1.35 g of LUPEROX® 26R in 11.2 g of MMA is introduced, the reactor temperature is raised to 105 ° C and maintained for 1 hour. The suspension is then cooled, filtered with the aid of a dripper, repulped with 7000 g of water, then drained again. This operation is performed 3 times. The trisequenced copolymer 2 is presented in the form of beads composed of PMMA-b-poly (butyl acrylate) -b-PMMA with a mean diameter of 334 μm. mass average in number: 61000 g / mol weight average mass: 185000 g / mol Trisequential copolymer 3 Stage 1: preparation of a solution comprising live butyl polyacrylate and butyl polyacrylate deactivated in MMA In a stirred 20 liter reactor 200 revolutions per minute, 14000 g of butyl acrylate are polymerized at 117 ° C in the presence of 140 g of DIAMINS at a conversion rate of 70% as measured by dry extraction. Butyl polyacrylate has the following molecular masses in PMMA equivalents: average peak mass: 97220 g / mol average mass in number: 67810 g / mol average weight mass: 106990 g / mol average mass in z: 148020 g / polimolecularity mol: 1.6 4240 g of the preceding mixture (ie comprising butyl polyacrylate and butyl acrylate) are heated at 70 ° C in the presence of 13.7 g of AIBN diluted in 30 g of butyl acrylate. An exotherm of approximately 25 ° C is observed, ie the temperature in the reactor rises to 95 ° C, then the reaction medium is kept at 70 ° C for 6 hours, then cooled to 30 ° C, and diluted with MMA until a solution comprising 45% by weight of butyl polyacrylate is obtained. This butyl polyacrylate corresponds to live butyl reactive polyacrylate, and deactivated butyl polyacrylate. Step 2: preparation of the tri-sequence copolymer 3 7000 g of deionized water, 509 g of a 5.3% solution of PAMS and 0.37 g of soda in a 20 liter reactor previously degassed and purged with nitrogen. This solution is brought to 70 ° C under an agitation of 200 revolutions per minute. When the temperature reaches 70 ° C, a solution of 4218 g of the solution prepared in the preceding stage 1 is displaced.

The reaction mixture is brought to 100 ° C for a period of 2 hours at which time a mixture of 3.7 g of octyl mercaptan diluted in 11.2 g of MMA is introduced. The reaction mixture is left under stirring at 100 ° C for one hour, then a mixture of 6.75 g of LUPEROX® 26R and 247 g of MMA is continuously introduced for 1 hour, then 1.35 g of LUPEROX® 26R into 11.25 g of MMA, and the temperature of the reactor is brought to 105 ° C. for 1 hour. Then the suspension is cooled, filtered with the help of a dripper, repulped with 7000 g of water then drained again. This operation is performed 3 times. The trisequenced copolymer 3 is presented in the form of beads composed of a mixture of PMMA-b-poly (butyl acrylate) -PMMA and poly (butyl acrylate), with a mean diameter of 168 μm. Average mass in number: 48650 g / mol Average mass in weight: 248200 g / mol Figure 4 represents an AFM plate of the product obtained. It is perceived that it presents a nanostructuring (phase microseparation) with phases (see the points that appear in clear) whose size is less than 100 nm (the scale of the plate is 5 μm). Trisequenced Copolymer 4 7150 g of deionized water are charged to a 20-liter reactor previously degassed and purged with nitrogen in the presence of 375 g of a 5.4% by weight solution of PAMS and 0.37 g of NaOH. This solution is brought to 70 ° C under an agitation of 200 revolutions per minute. When the temperature reaches 70 ° C, 4389 g of the live butyl polyacrylate solution are poured into the MMA obtained in step 1 in the preparation of the trisequenced copolymer 2. The reaction mixture is brought to 100 ° C over a period of two hours. hours, at the end of which a mixture of 3.7 g of octyl mercaptan diluted in 11.2 g of MAM is introduced. The reaction mixture is left under stirring at 100 ° C for one hour. At the end of this period, a mixture of 15 g of LUPEROX® 531 and 100 g of MMA is introduced in a single time, then the temperature of the reactor is brought to 120 ° C for 2 hours. At the end of this In this period, the reactor is cooled to 95 ° C and a solution of 4.5 g of potassium persulfate in 150 ml of water is introduced at once. The reaction mixture is maintained at 95 ° C for one hour. Then the suspension is cooled, filtered with the help of a colander, repulped with 7000 g of water then drained again. This operation is performed 3 times. The trisequenced copolymer is presented in the form of beads whose average size is 209 μm. The trisequenced copolymer is then granulated.

Average mass in number: 49300 g / mol Average mass in weight: 2Ó4000 g / mol Results (see Table I) It is verified that ABS only has a resilience of 50.6 kJ / m2 (Example 1). This falls when the ABS is coated by ALTUGLAS® V04 or DRT (Examples 2 and 3). In the presence of a ductile intermediate layer of trisequence copolymer, the resilience of the assembly rises again to the level of the ABS alone (Examples 5 to 12). The structure of Example 10 also has a high resistance to UV rays thanks to TINUVIN® P.

Table I Table I (Continued) ABS: MAGNUM 3904 marketed by DOW, which has a melt index of 1.5 g / 10 min (230 ° C, 3.8 kg) - thickness of 3 mm.

Claims (15)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as novelty, and therefore the content of the following is claimed as property: CLAIMS 1. Multilayer structure comprising in the order: • a protective layer (I) comprising a PMMA, • optionally a pigmented layer (II), • an intermediate ductile layer (III) comprising a sequenced copolymer of formula BAn composed: - of a polymer sequence B comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, and - of n polymeric sequences A, linked to the polymeric sequence B by covalent bonds, n denoting an integer comprised between 1 and 10, comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg greater than 0 ° C, • a layer of structural plastic (IV), the layers being arranged one above the other in the order (I) to (IV) indicated, and as if the pigmented layer were not present, the total thickness of layers (I) and (III) is greater than 310 μm. Multilayer structure according to claim 1, characterized in that the sequence B is obtained from a mixture MB comprising at least 60% by weight, advantageously at least 70%, preferably at least 80% of at least one monomer (met) acrylic that has a Tg lower than -5 ° C. Multilayer structure according to claim 1 or 2, characterized in that the Tg of sequence B is less than -5 ° C. Multilayer structure according to one of claims 1 to 3, characterized in that the sequences A are obtained from a mixture MA comprising at least 60% by weight, advantageously at least 70%, preferably at least 80% by weight minus one (meth) acrylic monomer having a Tg greater than 0 ° C. 5. Multilayer structure according to one of claims 1 to 4, characterized in that the A sequences have a Tg greater than 0 ° C. Multilayer structure according to one of claims 1 to 5, characterized in that sequence B and sequences A have an interaction parameter of Flory-Huggins XA_B > 0 at temperature ambient. Multilayer structure according to one of claims 1 to 6, characterized in that the sequenced copolymer is obtained by a process comprising the following steps: A. The sequence B is prepared by heating a mixture MB comprising at least 60% by weight of at least one (meth) acrylic monomer having a Tg of less than -5 ° C, in the presence of at least one alkoxyamine ZTn, the heating being carried out at a temperature sufficient to activate the alkoxyamine and polymerize the MB mixture until a conversion of at least 60%, B. Sequences A are prepared by heating the sequence B obtained in step 1 in the presence of an MA mixture, comprising at least 60% by weight of at least one methacrylic monomer of Tg higher than 0 ° C, carried out heating at a temperature sufficient to activate sequence B and polymerize the MA mixture. Multilayer structure according to one of claims 1 to 7, characterized in that the PMMA is reinforced for impact with the aid of at least one impact modifier. 9. Multilayer structure in accordance with one of claims 1 to 8, characterized in that the impact modifier ratio varies from 0 to 60 parts per 100 parts of PMMA. Multilayer structure according to one of claims 1 to 9, characterized in that the pigmented layer comprises at least one pigment dispersed in a thermoplastic resin, preferably in a PMMA. 11. Procedure to protect a structural plastic by superimposing in the order by extrusion, hot compression or multi-injection: • a protective layer (I) comprising a PMMA, • possibly a pigmented layer (II), • an intermediate ductile layer (IV) comprising a sequenced copolymer of formula BAn defined according to preceding claims 1 to 7, • a layer of structural plastic (IV), 12. Procedure to protect a structural plastic by coextruding in the order: • a protective layer (I) comprising a PMMA, • Eventually a pigmented layer (II), • a ductile layer intermediary (III) comprising a sequenced copolymer of formula BAn composed: • a layer of structural plastic (III), 13. The panel of the exterior façade comprising in the order: • a protective layer (I) comprising a PMMA, • optionally a pigmented layer (II) • an intermediate ductile layer (III) comprising a sequenced copolymer of formula BAn defined according to preceding claims 1 to 7. • a layer of PVC. The layers being arranged one above the other in the order (I) to (IV) indicated. 14. Use of a BAn block copolymer defined according to preceding claims 1 to 7 for the preparation of an intermediate ductile layer. 15. Use of the multilayer structure according to one of claims 1 to 10 for the manufacture of objects and articles of everyday life such as: • boxes or cases of mowers, cutters, nautical motorcycles, household appliances. ..; • of car roof chests; • body parts; • of mineralogical plates; • exterior wall panels for caravans and mobile homes; • of external panels of refrigerators; • shower cabin panels; • of building doors; • of window moldings; • of fences