Impact resistant methacrylic resin composition

An impact resistant methacrylic resin composition comprising a multi-layer graft copolymer (II) and a methyl methacrylate polymer (III);

• said multi-layer graft copolymer (II) being obtained by a sequential four-step polymerization procedure wherein in the first step, 5 to 50 parts by weight of a monomer mixture (A) comprising 57 to 43% by weight of at least one alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms, 7 to 12% by weight of styrene or its derivative, 35 to 45% by weight of at least one alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, and 0.1 to 10% by weight of at least one polyfunctional monomer having at least two functional groups selected from the group consisting of acryloyloxy groups and methacryloyloxy groups in one molecule thereof is polymerized.
• in the second step 95 to 50 parts by weight of a monomer mixture (B) comprising 69 to 89% by weight of at least one alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, 10 to 30% by weight of styrene or its derivative, 0.1 to 5% by weight of a graft-linking monomer and 0 to 5% by weight of a polyfunctional monomer having at least two functional groups selected from the group consisting of acryloyloxy groups and methacryloyloxy groups in one molecule thereof is polymerized in the presence of the polymer obtained in the first step, thereby to obtain a double-layer elastic copolymer (I);
• in the third step, 1 to 100 parts by weight of a monomer mixture (C-1) comprising 80 to 99.9% by weight of at least one alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms, 0 to 20% by weight of at least one alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, 0 to 10% by weight of at least one monomer selected from the group consisting of other vinyl monomers and vinylidene monomers and 0.1 to 3% by weight of at least one polyfunctional monomer having at least two functional groups selected from the groups consisting of acryloyloxy groups and methacryloyloxy groups in one molecule thereof is polymerized in the presence of 100 parts by weight of said double-layer elastic copolymer (I);
• in the fourth step, 10 to 899 parts by weight of a monomer mixture (C-2) comprising 100 to 80% by weight of at least one alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms, 0 to 20% by weight of at least one alkyl acrylate having an alkyl group with 1 to 8 carbon atoms and 0 to 10% by weight of at least one monomer selected from the group consisting of other vinyl monomers and vinylidene monomers is polymerized in the presence of the copolymer obtained in the third step, wherein the total amount of (C-1) and (C-2) ranges from 30 to 900 parts by weight and the weight ratio of both monomer mixtures (C-2)/(C-1) ranges from 0.5 to 50;
• and
• said methyl methacrylate polymer (III) comprising 80 to 100% by weight of methyl methacrylate units and 0 to 20% by weight of units of at least one copolymerizable monomer selected from the group consisting of other vinyl monomers and vinylidene monomers.