Highly transparent and tough-stiff styrene-butadiene block copolymer mixtures

1. A transparent mixture, comprising

a) from 25 to 75% by weight of a block copolymer A which comprises at least one hard block S composed of vinylaromatic monomers and comprises one or more soft blocks B A in each case composed of from 0 to 5% by weight of vinylaromatic monomers and from 95 to 100% by weight of dienes, where the proportion by weight of the hard blocks S in the block copolymer A is from 65 to 90% by weight;

b) from 5 to 25% by weight of a block copolymer B which comprises a star-shaped structure having at least two terminal hard blocks S 1 and S 2 with different molecular weight composed of vinylaromatic monomers and comprises one or more copolymer blocks (B/S) B in each case composed of from 20 to 60% by weight of vinylaromatic monomers and from 80 to 40% by weight of dienes, where the proportion by weight of the hard blocks S in the block copolymer B is from 40 to 70% by weight;

c) from 0 to 70% by weight of polystyrene or of a block copolymer C other than A and B, and

d) from 0 to 6% by weight of a plasticizer D,

where the entirety of components A) to D) gives 100% by weight.

2. The transparent mixture according to claim 1 , which comprises

a) from 35 to 55% by weight of the block copolymer A,

b) from 10 to 20% by weight of the block copolymer B, and

c) from 25 to 55% by weight of polystyrene or of a block copolymer C other than A and B.

3. The transparent mixture according to claim 1 , wherein the glass transition temperature Tg A of the soft blocks B A of the block copolymer A is in the range from −70° to −100° C.

4. The transparent mixture according to any of claim 1 , wherein the glass transition temperature Tg B of the soft blocks (B/S) B of the block copolymer B is in the range from −65° to 0° C.

5. The transparent mixture according to any of claim 1 , wherein the number-average molar mass M n of the block B A of the block copolymer A is in the range from 20 000 to 80 000 g/mol.

6. The transparent mixture according to any of claim 1 , wherein the number-average molar mass M n of the block (B/S) B of the block copolymer B is in the range from 50 000 to 150 000 g/mol.

7. The transparent mixture according to any of claim 1 wherein each of the block copolymers A and B has a star-shaped structure and the hard blocks S are terminal to the arms of the star.

8. The transparent mixture according to any of claim 1 , wherein the copolymer blocks (B/S) B of the block copolymer B have random distribution of the vinylaromatic monomers and dienes.

9. The transparent mixture according to claim 1 , wherein the block copolymer B comprises at least two successive copolymer blocks (B/S) B each having a monomer gradient from vinylaromatic monomers to dienes.

10. The transparent mixture according to claim 1 , wherein the star-shaped block copolymer B has terminal blocks S 1 whose number-average molar mass M n is in the range from 5000 to 30 000 g/mol and has terminal blocks S 2 whose number-average molar mass M n is in the range from 35 000 to 150 000 g/mol.

11. The transparent mixture according to claim 10 , wherein the block copolymer A has a star-shaped structure having terminal blocks S 1 whose number-average molar mass M n is in the range from 5000 to 30 000 g/mol and having terminal blocks S 2 whose number-average molar mass M n is in the range from 35 000 to 150 000 g/mol.

12. The transparent mixture according to claim 11 , wherein a molar ratio S 1 /S 2 for the block copolymer A is in the range from 0.5:1 to 10:1.

13. The transparent mixture according to claim 2 , wherein a glass transition temperature Tg A of soft blocks B A of the block copolymer A is in the range from −70° to −100° C.

14. The transparent mixture according to claim 2 , wherein a glass transition temperature Tg B of soft blocks (B/S) B of the block copolymer B is in the range from −65° to 0° C.

15. The transparent mixture according to claim 3 , wherein a glass transition temperature Tg B of soft blocks (B/S) B of the block copolymer B is in the range from −65° to 0° C.

16. The transparent mixture according to claim 2 , wherein a number-average molar mass M n of the block B A of the block copolymer A is in the range from 20 000 to 80 000 g/mol.

17. The transparent mixture according to claim 3 , wherein a number-average molar mass M n of the block B A of the block copolymer A is in the range from 20 000 to 80 000 g/mol.

18. The transparent mixture according to claim 4 , wherein a number-average molar mass M n of the block B A of the block copolymer A is in the range from 20 000 to 80 000 g/mol.

19. The transparent mixture according to claim 2 , wherein a number-average molar mass M n of the block (B/S) B of the block copolymer B is in the range from 50 000 to 150 000 g/mol.

20. The transparent mixture according to claim 3 , wherein a number-average molar mass M n of the block (B/S) B of the block copolymer B is in the range from 50 000 to 150 000 g/mol.

21. The transparent mixture according to claim 2 , which comprises c) from 25 to 55% by weight of polystyrene.

22. The transparent mixture according to claim 2 , which comprises at least 40% by weight of polystyrene.