Methods for controlling hardness of styrene-butadiene block copolymers

1. A method of controlling a conjugated diene monovinylarene copolymerization reaction, the method comprising:

(i) contacting a monovinylarene monomer, a conjugated diene monomer, and an initiator in a predetermined sequence under polymerization conditions in a polymerization reactor system, and thereafter coupling and/or terminating to form a conjugated diene monovinylarene block copolymer;

wherein the predetermined sequence comprises a dual charge of the monovinylarene monomer and the conjugated diene monomer; and

(ii) introducing a modifier into the polymerization reactor system before the dual charge to control a Shore A hardness of the copolymer, wherein the Shore A hardness of the copolymer decreases as an amount of the modifier introduced into the polymerization reactor system increases, and wherein the Shore A hardness of the copolymer is in a range from about 20 to about 95.

2. The method of claim 1 , wherein the modifier comprises an amine, a metal phenolate, a metal sulfonate, an ether, an alkali metal alkoxide, or a combination thereof.

3. The method of claim 1 , wherein the modifier comprises tetrahydrofuran (THF).

4. The method of claim 1 , wherein the modifier comprises potassium tert-amylate (KTA).

5. The method of claim 1 , wherein an amount of the modifier introduced into the polymerization reactor system is in a range from about 1:250 to about 1:10,000, based on the total moles of the modifier to the total moles of the monovinylarene monomer and the conjugated diene monomer.

6. The method of claim 1 , wherein:

the monovinylarene monomer is styrene; and

the conjugated diene monomer is a butadiene.

7. The method of claim 6 , wherein a kink resistance of tubing produced from the copolymer of step (ii) and tested in accordance with DIN EN 13868 is in a range from about 10 to about 32 mm.

8. The method of claim 1 , wherein:

the conjugated diene monovinylarene block copolymer is a styrene butadiene block copolymer;

a Shore A hardness of the copolymer is in a range from about 20 to about 95; and

an amount of the modifier introduced into the polymerization reactor system is in a range from about 1:500 to about 1:5,000, based on the total moles of the modifier to the total moles of the monovinylarene monomer and the conjugated diene monomer.

9. The method of claim 8 , wherein:

a pellet blocking force of the copolymer increases as the amount of the modifier introduced into the polymerization reactor system increases;

the copolymer has from about 55 to about 85 wt. % monovinylarene monomer content, based on the total weight of the copolymer; and

the conjugated diene monovinylarene block copolymer contains from 3 to 8 blocks.

10. The method of claim 1 , further comprising measuring the Shore A hardness, and adjusting an amount of the modifier introduced into the polymerization reactor system based on a difference between the measured Shore A hardness and a target Shore A hardness.

11. The method of claim 1 , wherein the predetermined sequence comprises two or more dual charges, and the modifier is introduced into the polymerization reactor system before each dual charge.

12. The method of claim 1 , wherein the block copolymer comprises from about 35 phm to about 80 phm monovinylarene monomer, and comprises polymer chains containing a block structure having formula (1):

S 1 −( SB ) 1   (1);

wherein:

S 1 is a monoblock of the monovinylarene monomer, wherein S 1 is from about 10 phm to about 45 phm of the copolymer; and

(SB) 1 is a mixed block of the conjugated diene monomer and the monovinylarene monomer, wherein the monovinylarene monomer content is from 20 wt. % to 80 wt. %, based on the total weight of (SB) 1 .

13. A process for producing a conjugated diene monovinylarene block copolymer with a target Shore A hardness, the process comprising:

(a) contacting a monovinylarene monomer, a conjugated diene monomer, and an initiator in a predetermined sequence under polymerization conditions in a polymerization reactor system, and thereafter coupling and/or terminating to form the copolymer;

wherein the predetermined sequence comprises a dual charge of the monovinylarene monomer and the conjugated diene monomer; and

(b) controlling an amount of a modifier introduced into the polymerization reactor system to produce the copolymer with the target Shore A hardness; wherein the target Shore A hardness is in a range from about 20 to about 95.

14. The process of claim 13 , wherein:

the Shore A hardness of the copolymer decreases as the amount of the modifier introduced into the polymerization reactor system increases; and

a target Shore A hardness is in a range from about 20 to about 95.

15. The process of claim 13 , wherein the copolymer is a styrene butadiene block copolymer.

16. The process of claim 15 , wherein the copolymer has a Mn in a range from about 10,000 to about 500,000 g/mol and a MFR in a range from about 1 to about 30 g/10 min; and a target Shore A hardness is in a range from about 35 to about 90.

17. The process of claim 16 , wherein the copolymer has from about 55 to about 85 wt. % monovinylarene monomer content, based on the total weight of the copolymer.

18. The process of claim 13 , wherein:

the monovinylarene monomer is styrene;

the conjugated diene monomer is a butadiene; and

a target Shore A hardness is in a range from about 40 to about 95.

19. The process of claim 18 , wherein:

the copolymer has from about 50 to about 95 wt. % monovinylarene monomer content, based on the total weight of the copolymer; and

a pellet blocking force of the copolymer decreases as the amount of the modifier introduced into the polymerization reactor system decreases.

20. The method of claim 1 , wherein a Shore A hardness of the copolymer is in a range from about 35 to about 90.