Block copolymer composition and transparent elastomeric articles produced therefrom

1. An elastomeric polymer blend composition comprising:

A) from 65 to 92 parts by weight of at least one elastomeric monovinylidene aromatic-conjugated diene block copolymer, having a monovinylidene aromatic content of less than 50 weight percent based on the total weight of the elastomeric copolymer, and a weight average molecular weight of from 50,000 to 400,000;

B) from 8 to 35 parts by weight of at least one thermoplastic monovinylidene aromatic-conjugated diene block copolymer, having a monovinylidene aromatic content of 60 weight percent or more based on the total weight of the thermoplastic copolymer, and a weight average molecular weight from 50,000 to 300,000; and

C) from 0 to 30 parts by weight of an extender oil, based on the total weight of A, B and C,

wherein the elastomeric polymer blend composition does not contain an amount of any polymer other than A and B greater than 5 weight percent of the blend, and

wherein a plaque comprised of the elastomeric polymer blend composition has a percent haze of less than 50 percent and a percent transparency of greater than 75 percent in accordance with ASTM Method D 1003-92.

2. The polymer blend composition of claim 1 wherein the elastomeric block copolymer (A) is selected from A-B-A triblock copolymers, A-B-A-B tetrablock copolymers, A-B-A-B-A pentablock copolymers, and mixtures thereof, wherein each A is independently a polymer block produced from a monovinylidene aromatic monomer and each B is independently, a polymer block produced from a conjugated diene and optionally a monovinylidene aromatic monomer.

3. The polymer blend composition of claim 1 wherein the thermoplastic block copolymer (B) is selected from A-B block copolymers, A-B-A triblock copolymers, A-B-A-B tetrablock copolymers, A-B-A-B-A pentablock copolymers, and mixtures thereof, wherein each A is independently a polymer block produced from a monovinylidene aromatic monomer and each B is independently, a polymer block produced from a conjugated diene and optionally a monovinylidene aromatic monomer.

4. The polymer blend composition of claim 1 wherein each monovinylidene aromatic monomer is selected from styrene, alpha-methylstyrene, vinyltoluene, vinylpyridine or mixtures thereof; and each conjugated diene is selected from 1,3-butadiene, isoprene, 1,3-pentadiene or mixtures thereof.

5. The polymer blend composition of claim 1 wherein each monovinylidene aromatic monomer block of the elastomeric block copolymer has a peak weight average molecular weight of 9,000 or more and each conjugated diene block of the elastomeric block copolymer has a peak weight average molecular weight of 50,000 or more.

6. The polymer blend composition of claim 1 wherein the block copolymer of (A) and/or the block copolymer of (B) is a radial block copolymer.

7. The polymer blend composition of claim 1 wherein the elastomeric block copolymer has a refractive index of from 1.5240 to 1.5526 and/or the thermoplastic block copolymer has a refractive index of 1.5526 to 1.5925 as measured using a pressed film of the polymer blend composition less than 0.020 inches (0.05 cm) thick using an Abbe-type refractometer at 25° C. according to ASTM Standard D-542.

8. The polymer blend composition of claim 1 wherein each monovinylidene aromatic monomer block of the thermoplastic block copolymer has a peak weight average molecular weight of 12,500 or more and each conjugated diene block of the thermoplastic block copolymer has a peak weight average molecular weight of 2,500 or more.

9. The polymer blend composition of claim 1 , having the following properties:

a tensile strength greater than 10.0 MPa;

a peak force at 200 percent elongation of greater than 0.7 MPa

a set of 15 percent or less;

a stress relaxation of 20 percent or less;

a percent haze of less than 50 percent; and

a percent transparency of greater than 75 percent.

10. A process for producing the composition of claim 1 comprising:

polymerizing a monovinylidene aromatic monomer and a diene monomer to produce an elastomeric block copolymer polymerization mixture comprising a block copolymer of less than 50 weight percent monovinylidene aromatic monomer, based on the total weight of the block copolymer;

polymerizing a monovinylidene aromatic monomer and a diene monomer to produce a thermoplastic block copolymer polymerization mixture comprising a block copolymer of at least 60 weight percent monovinylidene aromatic monomer, based on the total weight of the block copolymer;

contacting the elastomeric copolymer polymerization mixture with the thermoplastic copolymer polymerization mixture to form a blended polymerization mixture;

devolatilizing the blended polymerization mixture to form a blended polymer product, and

pelletizing the blended polymer product.

11. The composition of claim 1 formed into an article.

12. A composition, comprising:

A) from 65 to 92 parts by weight one or more elastomeric block copolymer(s) corresponding to the formulas A-B-R(-B-A) n and A-(BA-) x -BA, wherein

each A is independently a polymer block produced from a monovinylidene aromatic monomer;

each B is independently a polymer block produced from a conjugated diene and, optionally, a monovinylidene aromatic monomer;

R is the remnant of a multifunctional coupling agent;

n is an integer from 1 to 5; and

x is a real number from 0 to 4, and

 wherein at least 50 weight percent of the one or more elastomeric block copolymer(s) is comprised of a B block further comprised of isoprene, butadiene, or combinations thereof, and the monovinylidene aromatic content of one or more elastomeric block copolymer(s) is less than 50 weight percent based on the total weight of the one or more elastomeric block copolymer(s);

B) from 8 to 35 parts by weight of one or more thermoplastic block copolymer(s) corresponding to the formulas A-B-R(-B-A) n , A-(BA-) x -BA, and B y -(AB-) z -AB, wherein,

each A is independently a polymer block produced from a monovinylidene aromatic monomer;

each B is independently a polymer block produced from a conjugated diene and, optionally, a monovinylidene aromatic monomer;

R is the remnant of a multifunctional coupling agent;

n is an integer from 1 to 5;

x is a real number from 0 to 4;

y is 0 or 1; and

z is a real number from 0 to 4, and

 wherein less than 50 weight percent of the one or more thermoplastic block copolymer(s) is comprised of a B block further comprised of isoprene, butadiene, or combinations thereof, and the monovinylidene aromatic content of the one or more thermoplastic block copolymer(s) is at least 60 weight percent based on the total weight of the one or more thermoplastic block copolymer(s); and

C) from 0 to 35 parts by weight of an extender oil, based on the total weight of A, B and C,

 wherein the composition does not contain an amount of any polymer other than A and B greater than 5 weight percent of the blend, and

 wherein a plaque comprised of the composition has a percent haze of less than 50 percent and a percent transparency of greater than 75 percent in accordance with ASTM Method D 1003-92.

13. The composition of claim 12 , wherein the monovinylidene aromatic monomer is styrene.

14. The composition of claim 12 , wherein the one or more elastomeric block copolymer(s) and the one or more thermoplastic block copolymer(s) have a MFR of from about 0.1 to about 50 g/10 minutes.

15. The composition of claim 12 , wherein the one or more elastomeric block copolymer(s) is comprised of no more than 5 weight percent of a diblock of the formula B-A.

16. The composition of claim 12 , wherein the one or more elastomeric block copolymer(s) have a refractive index of from 1.5240 to 1.5526 as measured using a pressed film of the polymer blend composition less than 0.020 inches (0.05 cm) thick using an Abbe-type refractometer at 25° C. according to ASTM Standard D-542.

17. The composition of claim 12 , wherein the one or more thermoplastic block copolymer(s) have a refractive index of 1.5526 to 1.5925 as measured using a pressed film of the polymer blend composition less than 0.020 inches (0.05 cm) thick using an Abbe-type refractometer at 25° C. according to ASTM Standard D-542.

18. The composition of claim 12 formed into an article with the following properties:

a tensile strength greater than 10.0 MPa;

a peak force at 200 percent elongation of greater than 0.7 MPa;

a set of 15 percent or less;

a stress relaxation of 20 percent or less;

a percent haze of less than 50 percent; and

a percent transparency of greater than 75 percent.