Controlled rheology polypropylene heterophasic copolymers

Abstract

This invention relates to the use of a cyclic ketone peroxide of half-life time larger than one second at a temperature of 225° C., for producing a controlled rheology polypropylene heterophasic copolymer of melt index MI2 larger than 15 g/10 min, having simultaneously a very high impact resistance and a high flexural modulus.

1 . A polymer composition produced by the process of degrading a polypropylene (co)polymer with a cyclic ketone peroxide, said polymer composition characterized by an Izod notched impact strength for melt flow indices greater than 15 g/10 min that is at least 50% higher than the Izod notched impact strength for melt flow indices greater than 15 g/10 min of a comparative polymer composition produced by degrading said propylene (co)polymer with a linear peroxide under the same conditions of degrading.  
     
     
         2 . The polymer composition of  claim 1  produced by degrading a polypropylene (co)polymer that looses its impact strength when the melt flow index reaches a threshold value that increases with decreasing extrusion temperature.  
     
     
         3 . The polymer composition of  claim 1  produced by degrading said polypropylene (co)polymer in the presence of a cyclic ketone peroxide having at least two peroxide groups.  
     
     
         4 . The polymer composition of  claim 3  produced by degrading said propylene (co)polymer with 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.  
     
     
         5 . The polymer composition of  claim 3  wherein the propylene (co)polymer is degraded by extrusion at a temperature of from 160° C. to less than 200° C.  
     
     
         6 . The polymer composition of  claim 1  produced by degrading a polypropylene heterophasic copolymer, containing from 5 to 20 wt % of ethylene.  
     
     
         7 . The polymer composition of  claim 6  produced by degrading a polypropylene heterophasic copolymer containing from 9 to 15 wt % of ethylene.  
     
     
         8 . The polymer composition of  claim 6  produced by degrading a copolymer that looses its impact strength when the melt flow index reaches a threshold value that increases with increasing amount of ethylene.  
     
     
         9 . The polymer composition of  claim 1  characterized by an Izod notched impact strength that is at least twice that of the Izod notched impact strength of said comparative polymer composition.  
     
     
         10 . The polymer composition of  claim 1  characterized by a flexural modulus that is at least 30 Mpa higher than the flexural modulus of said comparative polymer composition.  
     
     
         11 . A method of degrading a polypropylene (co)polymer which comprises extruding said polypropylene (co)polymer with a cyclic ketone peroxide to form a solid product of said polypropylene (co)polymer having a melt index greater than 15 g/10 min with an Izod notched impact strength that is at least 50% higher and a flexural modulus that is at least 30 Mpa higher than the Izod notched impact strength and flexural modulus of a corresponding polypropylene (co)polymer degraded with a linear peroxide under similar conditions.  
     
     
         12 . The method of  claim 11  wherein said extrusion is carried out at an extrusion temperature of 200° C. or less.  
     
     
         13 . The method of  claim 11  wherein said cyclic ketone peroxide has a half-life of more than one second at a temperature of 225° C.  
     
     
         14 . The method of  claim 11  wherein said cyclic ketone peroxide has a half-life of from two to 10 seconds at a temperature of 225° C.  
     
     
         15 . The method of  claim 11  wherein said extrusion is carried out at a temperature of from 160° C. to less than 200° C.  
     
     
         16 . The method of  claim 15 , wherein the polypropylene (co)polymer is a polypropylene heterophasic copolymer containing from 5 to 20 wt % of ethylene.  
     
     
         17 . The method of  claim 11  wherein said polypropylene (co)polymer is a polypropylene heterophasic copolymer containing ethylene in an amount within the range of 9-15 wt %.  
     
     
         18 . The method of  claim 17  wherein said polypropylene heterophasic copolymer contains from 11 to 14 wt % ethylene.  
     
     
         19 . The method of  claim 11  wherein the extrusion temperature is within the range of 160-190° C.  
     
     
         20 . The method of  claim 11  wherein said cyclic ketone peroxide is 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.