Transparent mixtures of linear styrene-butadiene block copolymers

1. A mixture comprising linear block copolymers composed of vinylaromatic monomers and dienes of the structure

(I) S 1 -B 1 -S 2 and

(II) B 2 -S 3 , where

S 1 is a block composed of vinylaromatic monomers whose number-average molar mass M n is in the range from 40 000 to 100 000 g/mol,

each of S 2 and S 3 is a block composed of vinylaromatic monomers whose number-average molar mass Mn is in the range from 5000 to 20 000 g/mol,

each of B 1 and B 2 is one or more blocks composed of dienes or is copolymer blocks composed of dienes and of vinylaromatic monomers whose number-average molar mass M n is in the range from 15 000 to 100 000 g/mol, and

the molar ratio of the block copolymers (I)/(II) is in the range from 0.5 to 10.

2. The mixture according to claim 1 , wherein the (I)/(II) ratio of the block copolymers is in the range from 2 to 3.

3. The mixture as claimed in claim 1 , wherein the vinylaromatic monomer/diene ratio in the blocks B 1 and B 2 is in the range from 0.3 to 1.5.

4. The mixture according to claim 1 , wherein each of the blocks B 1 and B 2 is one or more copolymer blocks composed of dienes and of vinylaromatic monomers with random distribution.

5. The mixture according to claim 1 , wherein the number-average molar masses M n of

S 1 are in the range from 60 000 to 85 000 g/mol,

of each of S 2 and S 3 are in the range from 8000 to 17 000 g/mol,

and of each of B 1 and B 2 are in the range from 50 000 to 75 000 g/mol.

6. The mixture according to claim 1 , wherein each of the blocks B 1 and B 2 is composed of two copolymer blocks composed of dienes and of vinylaromatic monomers, where the vinylaromatic monomer/diene ratio in the first block is in the range from 1 to 1.5 and in the second block is in the range from 0.3 to 1.

7. The mixture according to claim 1 , wherein, respectively, the number-average molar masses M n of S 2 and S 3 and the number-average molar masses of B 1 and B 2 have the same value.

8. The mixture according to claim 1 , which comprises from 5 to 95 percent by weight of the linear block copolymers (I) and (II), and from 95 to 5 percent by weight of standard polystyrene or impact-resistant polystyrene.

9. A modified mixture obtainable via partial or complete hydrogenation of the mixtures according to claim 1 .

10. The mixture according to claim 9 , wherein the degree of hydrogenation of olefinic double bonds is at least 97% and the degree of hydrogenation of the vinylaromatic monomer units is at least 90%.

11. The mixture according to claim 8 , wherein more than 30%, based on the entirety of the diene units, of the copolymerized diene units are present in the 1,2-vinyl form.

12. A process for preparation of a mixture according to claim 1 , which comprises preparing each of the block copolymers (I) and (II) chronologically and/or spatially separate via sequential anionic polymerization of vinylaromatic monomers and of dienes using organic compounds of alkali metals as initiators, and then blending them in a (I)/(II) molar ratio in the range from 0.5 to 10.

13. A process for preparation of a mixture according to claim 7 , which comprises preparing the block copolymers (I) and (II) via sequential anionic polymerization of vinylaromatic monomers and of dienes using organic compounds of alkali metals as initiators simultaneously in a reactor via double initiation, comprising the joint feed of initiator I 1 and of vinylaromatic monomers in a first stage, and joint feed of initiator I 2 and of dienes or of dienes and of vinylaromatic monomers in a second stage, where the molar ratio of the amount of initiator I 1 of the first feed to the amount of initiator I 2 of the second feed is in the range from 0.5 to 10.

14. The mixture as claimed in claim 2 , wherein the vinylaromatic monomer/diene weight ratio in the blocks B 1 and B 2 is in the range from 0.3 to 1.5.

15. The mixture according to claim 2 , wherein each of the blocks B 1 and B 2 is one or more copolymer blocks composed of dienes and of vinylaromatic monomers with random distribution.

16. The mixture according to claim 3 , wherein each of the blocks B 1 and B 2 is one or more copolymer blocks composed of dienes and of vinylaromatic monomers with random distribution.

17. The mixture according to claim 2 , wherein the number-average molar masses M n of

S 1 are in the range from 60 000 to 85 000 g/mol,

of each of S 2 and S 3 are in the range from 8000 to 17 000 g/mol,

and of each of B 1 and B 2 are in the range from 50 000 to 75 000 g/mol.

18. The mixture according to claim 3 , wherein the number-average molar masses M n of

S 1 are in the range from 60 000 to 85 000 g/mol,

of each of S 2 and S 3 are in the range from 8000 to 17 000 g/mol,

and of each of B 1 and B 2 are in the range from 50 000 to 75 000 g/mol.

19. The mixture according to claim 4 , wherein the number-average molar masses M n of

S 1 are in the range from 60 000 to 85 000 g/mol,

of each of S 2 and S 3 are in the range from 8000 to 17 000 g/mol,

and of each of B 1 and B 2 are in the range from 50 000 to 75 000 g/mol.

20. The mixture according to claim 2 , wherein each of the blocks B 1 and B 2 is composed of two copolymer blocks composed of dienes and of vinylaromatic monomers, where the vinylaromatic monomer/diene ratio in the first block is in the range from 1 to 1.5 and in the second block is in the range from 0.3 to 1.