Crosslinked nanostructured cast sheets

1. A transparent and impact-resistant crosslinked acrylic composition comprising:

a brittle matrix (I) having a glass transition temperature of greater than 0° C.,

elastomeric domains having a characteristic dimension of less than 100 nm consisting of from 5 and 20% by weight macromolecular sequences (11) having a flexible nature with a glass transition temperature of less than 0° C., characterized by a number-average molecular weight of between 30,000 and 500,000 g/mol, and

between 0.1 and 2% by weight of a crosslinking agent, with respect to the crosslinked polymer material, wherein said crosslinking agent is selected from the group consisting of one 1,4-butylene glycol dimethacrylate, and 1,3-butylene glycol dimethacrylate, and mixtures thereof,

wherein said macromolecular sequence does not contain any diene.

2. The composition as claimed in claim 1 , in which the macromolecular sequences (II) are prepared from monomers selected from the group consisting of acrylic monomers of formula CH 2 ═CH—C(═O)—O—R 1 , where R 1 denotes a hydrogen atom or a linear, cyclic or branched C 1 -C 40 alkyl group optionally substituted by a halogen atom or a hydroxyl, alkoxy, cyano, amino or epoxy group, methacrylic monomers of formula CH 2 ═C(CH 3 )—C(═O)—O—R 2 , where R 2 denotes a hydrogen atom or a linear, cyclic or branched C 1 -C 40 alkyl group optionally substituted by a halogen atom or a hydroxyl, alkoxy, cyano, amino or epoxy group, and vinylaromatic monomers.

3. The composition as claimed in claim 1 , in which the macromolecular sequences (II) are prepared from butyl acrylate and styrene in a butyl acrylate/styrene ratio by weight of between 70/30 and 90/10.

4. The composition as claimed in claim 1 , further comprising the decomposition products of an alkoxyamine of general formula Z(-T) n in which Z denotes a polyvalent group, T denotes a nitroxide and n is an integer greater than or equal to 2.

5. The composition as claimed in claim 4 , in which the alkoxyamine corresponds to the following formula:

SG1 being N-(tert-butyl)-1-diethylphosphono-2,2-dimethylpropyl nitroxide.

6. The composition as claimed in claim 4 , in which the alkoxyamine corresponds to the following formula:

7. A process for the preparation of a transparent and impact-resistant crosslinked acrylic composition consisting of a brittle matrix (I) having a glass transition temperature of greater than 0° C. and of elastomeric domains having a characteristic dimension of less than 100 nm consisting of macromolecular sequences (II) having a flexible nature with a glass transition temperature of less than 0° C., characterized by a number-average molecular weight of between 30,000 and 500,000 g/mol, in which the content of crosslinking agent is between 0.1 and 2% by weight, with respect to the crosslinked polymer material, comprising the following steps:

1. preparing the macromolecular sequences (II) by mixing, with one or more monomer(s) intended to form the macromolecular sequences (II), an alkoxyamine of general formula Z(-T) n , in which Z denotes a polyvalent group, T denotes a nitroxide and n is an integer greater than or equal to 2;

2. mixing the macromolecular sequences (II) of stage 1 with methyl methacrylate, the crosslinking agent, optionally at least one comonomer M and at least one radical initiator;

3. casting the mixture obtained in stage 2 in a mold and then heating it according to a temperature cycle in order to obtain a cast sheet.

8. The process as claimed in claim 7 , further comprising adding to the mixture which is cast in the mold during stage 3 of the process, another ingredient chosen from:

opacifying fillers, in the form of pastes prefabricated in a dialkyl phthalate plasticizer;

colored organic dyes or colored inorganic pigments;

plasticizers;

UV-stabilizing additives, used at contents of 0 to 1000 ppm, with respect to the mixture which is cast in the mold;

light or heat stabilizers;

antioxidants;

flame-retarding additives;

thickening agents;

mold-release agents used at contents of 0 to 500 ppm, with respect to the mixture which is cast in the mold;

inorganic or organic fillers intended to scatter light.

9. An item comprised of the composition as claimed in claim 1 .

10. The item as claimed in claim 9 wherein said item is part of a window, noise-reducing wall, flat screen, or bathroom fitting.

11. The composition as claimed in claim 2 , wherein said acrylic monomers are selected from the group consisting of acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, glycidyl acrylate, hydroxyalkyl acrylates and acrylonitrile, said methacrylic monomers are selected from the group consisting of methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, glycidyl methacrylate, hydroxyalkyl methacrylates and methacrylonitrile, and said vinylaromatic monomers are selected from the group consisting of styrene, substituted styrenes, α-methylstyrene, monochlorostyrene and tert-butylstyrene.

12. The process of claim 8 , wherein said opacifying fillers are selected from the group consisting of TiO 2 and BaSO 4 , in the form of pastes prefabricated in a dialkyl phthalate plasticizer; said UV-stabilizing additive is 2-(2H-benzotriazol-2-yl)-p-cresol and bis(2,2,6,6-tetramethyl-4-piperidyl)sebaceate; said UV-stabilizing additive is used at 50 to 500 ppm, with respect to the mixture which is cast in the mold; said light or heat stabilizers is 2-(2H-benzotriazol-2-yl)-p-cresol and bis(2,2,6,6-tetramethyl-4-piperidyl)sebaceate; said flame-retarding additive is tris(2-chloropropyl) phosphate; said thickening agent is cellulose acetate butyrate; said mold-release agent is dioctyl sodium sulfosuccinate, used at 0 to 200 ppm, with respect to the mixture which is cast in the mold; and said inorganic or organic fillers are selected from the group consisting of polyamides, polytetrafluroethylene (PTFE) and BaSO 4 .