Polycarbonate-block copolymer blend with improved solvent and impact resistance

Abstract

A modified polycarbonate composition comprising a blend of a bisphenol A-based polycarbonate and from greater than about 5% and less than about 15% by weight of a high molecular weight hydrogenated styrene-butadiene-styrene triblock copolymer has dramatically improved environmental stress crack resistance as well as improved impact resistance properties.

What is claimed is: 
     
       1. A toughened polycarbonate composition with improved environmental stress crack resistance comprising: an aromatic polycarbonate; and   an alkenyl-arene-diene-alkenyl-arene block copolymer in an amount greater than 5% by weight of the composition and effective to improve the environmental stress crack resistance of the composition relative to the aromatic polycarbonate, but in an amount less than that which adversely affects the molding properties of the blend.   
     
     
       2. The composition of claim 1, wherein the block copolymer is present in an amount greater than from about 5% to less than about 15% by weight of the composition. 
     
     
       3. The composition of claim 1, wherein the average molecular weight of the block copolymer is greater than about 70,000. 
     
     
       4. The composition of claim 1, wherein the block copolymer is a linear block copolymer of hydrogenated styrene-butadiene-styrene. 
     
     
       5. The composition of claim 1, wherein the block copolymer is a star block copolymer of styrene and hydrogenated butadiene. 
     
     
       6. The composition of claim 1, wherein the aromatic polycarbonate is a bisphenol A-based polycarbonate. 
     
     
       7. The composition of claim 1, wherein the aromatic polycarbonate is an aromatic ester copolycarbonate. 
     
     
       8. The composition of claim 1, further comprising an engineering resin present in an amount of less than about 50% by weight of the composition. 
     
     
       9. The composition of claim 2, wherein the block copolymer is present in an amount of from about 8% to about 12% by weight of the composition. 
     
     
       10. The composition of claim 4, wherein the molecular weight of the block copolymer is greater than about 130,000. 
     
     
       11. The composition of claim 8, wherein the engineering resin is selected form the group consisting of acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyethylene terephthalate, nylon, polyacetal resin and mixtures thereof. 
     
     
       12. A thermoplastic blend comprising: an aromatic polycarbonate; and   a hydrogenated styrene-butadiene-styrene block copolymer present in an amount of greater than about 5% to less than about 15% by weight of the blend.   
     
     
       13. The blend of claim 12, wherein the block copolymer has a molecular weight of greater than about 130,000. 
     
     
       14. The blend of claim 12, wherein the block copolymer is present in an amount of about 10% by weight of the blend. 
     
     
       15. The blend of claim 12, wherein the polycarbonate is bisphenol A polycarbonate. 
     
     
       16. The blend of claim 12, further comprising less than about 50% by weight of an engineering resin. 
     
     
       17. A polycarbonate blend comprising: a bisphenol A-based polycarbonate; and   a hydrogenated styrene-butadiene-styrene triblock copolymer discretely dispersed in the blend, the copolymer being of a molecular weight and present in an amount greater than 5% by weight of the composition and effective to significantly improve the environmental stress crack resistance of the blend relative to the polycarbonate.   
     
     
       18. The blend of claim 17, wherein the triblock copolymer has a molecular weight of greater than about 130,000 and is present in an amount of about 8% to about 12% by weight of the blend. 
     
     
       19. The blend of claim 17, further comprising less than about 50% by weight of an engineering resin selected from the group consisting of acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyethylene terephthalate, nylon, polyacetal resin and mixture thereof. 
     
     
       20. The blend of claim 18, wherein the triblock copolymer has a molecular weight of about 175,000 and is present in an amount of about 10% by weight of the blend.