Non-sticky, soft and transparent styrenic thermoplastic elastomers

1. A thermoplastic elastomer composition comprising components a), b), and c):

a) 97.1 to 90.9 wt.-% of at least one star-shaped block copolymer A of the structure

[S 1 -(S/B) k -(S/B) l -(S/B) m -S 2 ] n -X  (I),

where S 1 and S 2 are polymer blocks made from at least one vinylaromatic monomer and S/B are random copolymer blocks made from at least one vinylaromatic monomer and at least one diene forming a soft phase; X is a coupling center derived from a polyfunctional coupling agent;

b) 2.9 to 9.1 wt.-% of at least one plasticizer B; and

c) 0 to 2 wt.-% of further additives C;

wherein the sum of components a), b) and c) is 100 wt.-%;

the arms S 1 -(S/B) k -(S/B) l -(S/B) m -S 2 are identical;

the proportion of the blocks S 1 and S 2 (forming a hard phase), based on the entire block copolymer A, is from 24 to 40 wt.-%;

the vinylaromatic monomer/diene (=S/B) ratio of all of the blocks (S/B) is from 1/0.45 to 1/2.5;

the S/B-ratio of the blocks (S/B) k , (S/B) l and (S/B) m is different from each other;

the S/B-ratio of the blocks (S/B) k and (S/B) m is lower than the S/B-ratio of the block(s) (S/B) l ;

the weight ratio of blocks S2/S1 is from 0.1 to 0.8;

the weight average molar mass M w of the block copolymer A is from 200,000 to 350,000 g/mol;

n is a natural number from 3 to 8;

k and m are each 1; and

l is a natural number of at least 1.

2. The thermoplastic elastomer composition according to claim 1 comprising components a), b), and c) in the following amounts:

a) 96.2 to 91.7 wt.-%;

b) 3.8 to 8.3 wt.-%; and

c) 0 to 2 wt.-%.

3. The thermoplastic elastomer composition according to claim 1 , wherein the at least one plasticizer B is mineral oil.

4. The thermoplastic elastomer composition according to claim 1 which melt mass flow index (measured on a polymer melt at 200° C. and 5 kg load according to ISO 1133-1:2011) is in the range of from 8 to 16 cm 3 /10 min.

5. The thermoplastic elastomer composition according to claim 1 , wherein n is a natural number from 3 to 5.

6. The thermoplastic elastomer composition according to claim 1 , wherein X is a coupling center derived from epoxidized linseed oil or epoxidized soybean oil.

7. Thermoplastic elastomer composition according to claim 1 , wherein M w of the block copolymer A is from 210,000 to 320,000 g/mol.

8. The thermoplastic elastomer composition according to claim 1 , wherein Mw of the polymer block S 1 is in the range of from 18,000 to 36,000 g/mol; and Mw of the polymer block S 2 is in the range of from 4000 to 8100 g/mol.

9. The thermoplastic elastomer composition according to claim 1 , wherein the weight ratio of blocks S 2 /S 1 of block copolymer A is from 0.1 to 0.6.

10. The thermoplastic elastomer composition according to claim 1 , wherein the S/B-ratio of the copolymer block (S/B) k is from 0.5 to 1.0; the S/B-ratio of the copolymer block(s) (S/B) l is from 0.5 to 1.2; and the S/B-ratio of the copolymer block (S/B) m is from 0.3 to 0.8.

11. The thermoplastic elastomer composition according to claim 1 , wherein the weight average molar mass M w of the copolymer blocks (S/B) k , (S/B) l and (S/B) m is different from each other; Mw (S/B) k is in the range of from 13,800 to 26,900 g/mol; Mw (S/B) l is in the range of from 21,200 to 41,000 g/mol; and Mw (S/B) m is in the range of from 11,500 to 23,000 g/mol.

12. A process for the preparation of a thermoplastic elastomer composition according to claim 1 , wherein component a) is introduced continuously into an extruder and then component b) and optionally further components c) are metered in.

13. A process for the preparation of a thermoplastic elastomer composition according to claim 1 , wherein component b) and optional component c)—as such or in solution—are added into a solution of block copolymer A, then to homogenize the liquids, and subsequently to free the product from the solvent.

14. A shaped article produced from the thermoplastic elastomer composition according to claim 1 .

15. A method of using a thermoplastic elastomer composition according to claim 1 for medical applications.

16. A star-shaped block copolymer A according to claim 1 .

17. A process for the preparation of block copolymer A of formula (I) according to claim 1 characterized by

i) a single initiation,

ii) first addition and polymerization of vinyl aromatic monomer,

iii) at least 3 times addition and polymerization of a vinyl aromatic monomer and diene mixture,

iv) second addition and polymerization of vinyl aromatic monomer, and

v) a coupling step after the addition and polymerization of the vinylaromatic monomers of the last polymer block.