Propylene-based polymer compositions having a high molecular weight tail
Processes for forming a polypropylene composition are provided herein comprising the steps of making a first propylene-based copolymer having a molecular weight distribution between 3 to 8.5, and making a second propylene-based polymer in the presence of the first propylene-based polymer to produce the polypropylene composition having a high molecular weight tail in the amount of between 1.0 wt. % and 10.0 wt. %. The polypropylene compositions produced have a broad molecular weight distribution and high molecular weight tail to provide improved stiffness while retaining toughness.
1 . A process for forming a polypropylene composition comprising the steps of
making a first propylene-based polymer having a molecular weight distribution between about 3 to about 8.5; and
making a second propylene-based polymer in the presence of the first propylene-based polymer to produce the polypropylene composition having an Mz of at least 1,000,000 grams/mole;
wherein the first propylene-based polymer and/or the second propylene-based polymer are made in the presence of a catalyst system comprising a blend of tetraethoxysilane (TEOS) and dicyclopentyldimethoxysilane (DCPMS).
2 . The process of claim 1 , wherein the first propylene-based polymer is made in the presence of a catalyst system comprising a Ziegler-Natta catalyst and a first external electron donor under a polymerization temperature of between about 60° C. and about 80° C. to produce the first propylene-based polymer.
3 . The process of claim 1 , wherein the first propylene-based polymer is a homopolymer.
4 . The process of claim 1 , wherein the polypropylene composition has a Notched Izod impact according to ASTM D256 in a range of 0.25 ft-lbs/in to 15 ft-lbs/in.
5 . The process of claim 1 , wherein the first propylene-based polymer is made by a slurry phase polymerization in a slurry phase polymerization reactor.
6 . The process of claim 1 , wherein the second propylene-based polymer is made by a gas phase polymerization in a gas phase polymerization reactor.
7 . The process of claim 1 , wherein the second propylene-based polymer is made in the presence of a different catalyst system than the first propylene-based polymer.
8 . The process of claim 1 , wherein the catalyst system comprises two different catalysts.
9 . The process of claim 1 , wherein the catalyst system comprises a combination of three different catalysts.
10 . The process of claim 5 , wherein the slurry phase polymerization is performed in the slurry polymerization reactor at a pressure in a range of about 430 psig to about 580 psig.
11 . The process of claim 5 , wherein the slurry phase polymerization is performed in the slurry polymerization reactor at a temperature in a range of about 60° C. to about 80° C.
12 . The process of claim 6 , wherein the gas phase polymerization is performed in the gas phase polymerization reactor at a pressure in a range of about 150 psig to about 350 psig.
13 . The process of claim 6 , wherein the gas phase polymerization is performed in the gas phase polymerization reactor at a temperature in a range of about 60° C. to about 100° C.
14 . The process of claim 5 , wherein the slurry phase polymerization is performed in the slurry phase polymerization reactor at a residence time in a range of about 30 minutes to about 120 minutes.
15 . The process of claim 6 , wherein the gas phase polymerization is performed in the gas phase polymerization reactor at a residence time in a range of about 30 minutes to about 240 minutes.
16 . The process of claim 1 , wherein the polypropylene composition has a flex modulus of greater than about 175 kpsi and a Notched Izod impact greater than 0.3 ft.-lbs./in.