Core-hydrogenated block copolymers having an asymmetric structure
The invention relates to core-hydrogenated block copolymers composed of vinyl aromatic monomers and dienes having at least two blocks S, which are of different molecular weights and ate comprised of vinyl aromatic monomers. The invention also relates to mixtures containing core-hydrogenated polysterene and to methods for the production thereof.
1. A ring-hydrogenated block copolymer made from vinylaromatic monomers and from dienes, which has at least two blocks S made from vinylaromatic monomers, and which has a block S 1 with a molar Mass M n of at least 30 000 g/mol and a block S 2 with a molar mass M n in the range from 5 000 to 25 000 g/mol.
2. A ring-hydrogenated block copolymer as claimed in claim 1 , which has a block S 1 with a molar mass M n in the range from 30000 g/mol to 100 000 g/mol and a block S 2 with a molar mass M n in the range from 10 000 to 25 000 g/mol.
3. A ring-hydrogenated block copolymer as claimed in claim 1 , wherein the degree of hydrogenation of the vinylaromatic monomer units is at least 90%.
4. A ring-hydrogenated block copolymer as claimed in claim 1 , wherein the proportion of the diene units prior to hydrogenation is not more than 50% by weight, based on the entire block copolymer.
5. A ring-hydrogenated block copolymer as claimed in claim 1 , wherein prior to hydrogenation more than 30% of the copolymerized diene units, based on the total of the diene units, are present in the 1,2-vinyl form.
6. A ring-hydrogenated block copolymer as claimed in claim 1 , which prior to hydrogenation has a copolymer block (S/B) made from vinylaromatic monomers and from dienes with random distribution.
7. A ring-hydrogenated block copolymer as claimed in claim 1 , which is composed of styrene as vinylaromatic monomer and butadiene or isoprene as diene.
8. A mixture comprising
a) from 10 to 90% by weight of ring-hydrogenated block copolymers as claimed in claim 1 , and
b) from 90 to 10% by weight of ring-hydrogenated polystyrene.
9. A process for preparing ring-hydrogenated block copolymers as claimed in claim 1 , encompassing the steps of:
a) sequential anionic polymerization of the vinylaromatic monomers and dienes, using an organolithium initiator,
b) terminating the polymerization by using a protic terminator or a coupling agent, and
c) hydrogenating the resultant block copolymers, using a hydrogenation catalyst.
10. A process as claimed in claim 9 , wherein step a) is carried out in a cycloaliphatlc hydrocarbon as solvent, and in the presence of from 0.3 to 0.5 percent by volume, based on the solvent, of an ether.
11. Optical media comprising the block copolymer as claimed in claim 1 .