Blends of styrene/butadiene block copolymers
A blend comprising a) from 5 to 40% by weight of a linear block copolymer of vinylaromatic monomers and dienes of the structure (I) S 1 —(B/S) 1 —S 2 having a flexible phase fraction (B/S) 1 of not more than 55% by weight, based on the block copolymer (I) and b) from 95 to 60% by weight of a linear block copolymer of vinylaromatic monomers and dienes of the structure (II) S 3 —(B/S) 2 —S 4 having a flexible phase fraction (B/S) 2 of at least 65% by weight, based on the block copolymer (II), where S 1 is a block of vinylaromatic monomers having a number average molar mass M n in the range from 40 000 to 100 000 g/mol, S 2 , S 3 and S 4 are in each case blocks of vinylaromatic monomers having a number average molar mass M n in the range from 5000 to 20 000 g/mol, (B/S) 1 and (B/S) 2 are in each case copolymer blocks of dienes and vinylaromatic monomers having a number average molar mass M n in the range from 15 000 to 40 000 g/mol.
1. A blend comprising
a) from 10 to 30% by weight of a linear block copolymer of vinylaromatic monomers and dienes of the structure (I) S 1 —(B/S) 1 —S 2 having a flexible phase fraction (B/S) 1 of not more than 55% by weight, based on the block copolymer (I) and
b) from 90 to 70% by weight of a linear block copolymer of vinylaromatic monomers and dienes of the structure (II) S 3 —(B/S) 2 —S 4 having a flexible phase fraction (B/S) 2 of at least 65% by weight, based on the block copolymer (II),
where S 1 is a block of vinylaromatic monomers having a number average molar mass M n in the range from 40 000 to 100 000 g/mol,
S 2 , S 3 and S 4 are in each case blocks of vinylaromatic monomers having a number average molar mass M n in the range from 5000 to 20 000 g/mol, (B/S) 1 and (B/S) 2 are in each case copolymer blocks of dienes and vinylaromatic monomers having a number average molar mass M n from 15 000 to 40 000 g/mol and wherein the blend has a modulus of elasticity in the range from 50 to 200 mPa.
2. The blend according to claim 1 , wherein the vinylaromatic monomer/diene ratio in blocks (B/S) 1 or (B/S) 2 is in the range from 0.3 to 0.7.
3. The blend according to claim 1 , wherein the blocks (S/B) 1 and (S/B) 2 are in each case copolymer blocks of dienes and vinylaromatic monomers having random distribution.
4. The blend according to claim 1 , wherein the number average molar masses M n of S 1 is in the range from 45 000 to 70 000, of S 2 , S 3 , and S 4 are in each case in the range from 8000 to 17 000 g/mol, and of (B/S) 1 and (B/S) 2 are in each case in the range from 18 000 to 30 000 g/mol.
5. The blend according to claim 1 , wherein the blocks S 3 and S 4 have the same number average molar masses M n .
6. The blend according to claim 1 , wherein in each case the number average molar masses M n of S 2 and S 4 and the number average molar masses M n of (B/S) 1 and (B/S) 2 have the same value.
7. A process for the preparation of a blend according to claim 1 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal initiators in different reactors and are then mixed.
8. The process for the preparation of a blend according to claim 6 , wherein the block copolymers (I) and (II) are initiated simultaneously in a reactor by dual, joint metering of organo-alkali metal initiators and vinylaromatic monomers and are polymerized by sequential anionic polymerization of vinylaromatic monomers and dienes.
9. A process for the preparation of a blend according to claim 1 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal initiators in different reactors and are then mixed.
10. A process for the preparation of a blend according to claim 2 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal in different reactors and are then mixed.
11. A process for the preparation of a blend according to claim 3 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal initiators in different reactors and are then mixed.
12. A process for the preparation of a blend according to claim 4 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal initiators in different reactors and are then mixed.
13. A process for the preparation of a blend according to claim 5 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal initiators in different reactors and are then mixed.
14. A process for the preparation of a blend according to claim 6 , wherein the block copolymers (I) and (II) are prepared in each case by sequential anionic polymerization of vinylaromatic monomers and dienes with organo-alkali metal initiators in different reactors and are then mixed.
15. The blend according to claim 1 , wherein a ratio for the average number molar masses of S 1 to S 2 is in the range of 5 to 8.