Ductile and transparent thermoplastic compositions comprising an amorphous matrix and a block copolymer
The invention concerns transparent materials having good impact resistance, a high modulus and good heat resistance. The inventive materials comprise an amorphous matrix, preferably based on styrene/methyl methacrylate statistical copolymer whether impact-reinforced of not with a standard additive, and a block copolymer having at least an elastomeric block and at least a block partly or entirely compatible with the amorphous matrix.
1 . A transparent polymeric composition having good impact strength, a high modulus, and good heat resistance, comprising:
from 50% to 90% by weight of a thermoplastic matrix (I) with a refractive index n 1 , wherein matrix (I) is a homopolymer or a copolymer comprising at least one monomer unit selected from the group consisting of styrene, acrylonitrile, acrylic acid, and short-chain alkyl (meth)acrylates;
from 0 to 40% by weight of an impact additive (II) with a refractive index n 2 ; and
from 10% to 50% by weight of a block copolymer (III) with a refractive index n 3 ;
the difference between the refractive indices, taken two by two, being less than or equal to 0.01.
2 . The composition of claim 1 , wherein the block copolymer III conforms to the following general formula -Y-B-Y′- in which
B is an elastomer block which is thermodynamically incompatible with blocks Y and Y′,
Y and Y′ can be the same or different,
at least one of the two blocks Y and Y′ is totally or partially compatible with the thermoplastic matrix (I).
3 . The composition of claim 2 , wherein B comprises one or more monomer units selected from the group consisting of butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and 2-phenyl-1,3-butadiene.
4 . The composition of claim 3 , wherein B comprises butadiene monomer units.
5 . The composition of claim 3 , wherein B comprises isoprene monomer units.
6 . The composition of claim 2 , wherein Y and Y′ comprise at least one monomer unit selected from the group consisting of styrene and short-chain alkyl methacrylates.
7 . The composition of claim 6 , wherein Y is a block composed predominantly of styrene and wherein Y′ is a block composed predominantly of methyl methacrylate monomer units.
8 . The composition of claim 6 , wherein Y and Y′ are blocks composed predominantly of methyl methacrylate monomer units.
9 . The composition of claim 7 , wherein Y′ comprises at least 60% of syndiotactic polymethyl methacrylate.
10 . The composition of claim 8 , wherein Y and Y′ each contain at least 60% of syndiotactic polymethyl methacrylate.
11 . The composition of claim 1 , wherein the amorphous matrix I comprises at least one monomer unit selected from the group consisting of styrene, acrylonitrile, acrylic acid, and short-chain alkyl (meth)acrylates.
12 . The composition of claim 11 , wherein I comprises a mixture composed of 0 to 55% by weight of styrene monomer units and from 45% to 100% by weight of methyl methacrylate monomer units.
13 . The composition of claim 1 , wherein the additive II is a core-shell copolymer comprising an elastomer core and a rigid shell which is compatible with the amorphous matrix I.
14 . An article comprising the composition of claim 1 , wherein said article is formed by a melt state conversion selected from the group consisting of injection molding, extrusion and calendaring.
15 . The composition of claim 6 , wherein Y and Y′ comprise methyl methacrylate units.
16 . The composition of claim 11 , wherein the amorphous matrix I comprises methyl methacrylate monomer units.