Impact modification of polypropylene with styrene/isoprene triblock copolymers

Abstract

Compositions consisting essentially of from 60% to 95% by weight of the polymer components of a high flow polypropylene and from 40% to 5% by weight of a polystyrene-hydrogenated polyisoprene-polystyrene block copolymer have excellent low temperature impact strength and high heat distortion temperature for molding large automobile parts.

What is claimed is: 
     
       1. A polypropylene molding composition, comprising: from 60% to 95% by weight of the polymer components of a high flow polypropylene having a melt flow from 50 to 80 dg/min, wherein the polypropylene is selected from a group consisting of homopolymers of propylene, random copolymers of propylene and an olefin selected from ethylene and C 4  -C 10  alpha-olefins, and random terpolymers of propylene with two alpha-olefins selected from ethylene and C 4  -C 10  alpha-olefins; and   from 40% to 5% by weight of the polymer components of a polystyrene-hydrogenated polyisoprene-polystyrene block copolymer having a peak molecular weight from 4,500 to 8,000 for each polystyrene block and a polystyrene content from 13% to 20%.   
     
     
       2. The composition of claim 1, wherein each polystyrene block in the block copolymer has a peak molecular weight from 5,000 to 5,500. 
     
     
       3. The composition of claim 1, wherein the high flow polypropylene comprises from 80% to 95% of the polymer components. 
     
     
       4. The composition of claim 1, further comprising up to about 80 parts of a filler per 100 parts of the total polymer components.