Nitroso-modified Ziegler-Natta catalyst system
A modified Ziegler-Natta catalyst system, a method for preparing the catalyst system, and a process for polymerizing an olefin in the presence of the catalyst system are disclosed. The catalyst system comprises a titanium compound, an aluminum compound, and a nitroso compound. Improved polyolefin properties, such as high molecular weight, are obtained.
1. A process for making polyethylene, comprising polymerizing ethylene and an olefin selected from the group consisting of 1-butene, 1-hexene, and 1-octene in the presence of a modified Ziegler-Natta catalyst system, wherein the catalyst system comprises: (a) a titanium compound; (b) an aluminum compound selected from the group consisting of trialkyl aluminums, dialkyl aluminum halides, alkyl aluminum dihalides, and combinations thereof; and (c) one or more aliphatic nitroso compounds; wherein the weight-average molecular weight (Mw) of the polyethylene is increased compared with that of a polyethylene produced using the catalyst system without the nitroso compound.
2. The process of claim 1 wherein the titanium compound is titanium tetrachloride.
3. The process of claim 1 wherein the nitroso compound has the structure:
wherein R 1 is aliphatic C 1 -C 16 hydrocarbyl.
4. The process of claim 1 wherein the molar ratio of nitroso compound to titanium is from 50:1 to 1:1.
5. The process of claim 1 wherein the modified Ziegler-Natta catalyst system is prepared by a method comprising: (a) reacting a one or more aliphatic nitroso compounds with an aluminum compound selected from the group consisting of trialkyl aluminums, dialkyl aluminum halides, alkyl aluminum dihalides, and combinations thereof; and (b) contacting the reaction mixture from step (a) with a titanium compound.
6. The process of claim 1 wherein the presence of the nitroso compound in the modified Ziegler-Natta catalyst system provides at least a 30% increase in the weight-average molecular weight of the polyethylene.
7. The process of claim 1 wherein said one or more of said nitroso compounds comprises 2-methyl-2-nitrosopropane dimer.