FIELD OF THE INVENTION

The present disclosure relates to polymerization processes for producing ethylene-based plastomers and elastomers, and more particularly, relates to slurry, solution, and gas phase polymerization processes using metallocene catalyst systems containing chemically-treated solid oxides to produce such ethylene-based plastomers and elastomers.

BACKGROUND OF THE INVENTION

Ethylene-based copolymers can be produced using various combinations of catalyst systems and polymerization processes. In some end-use applications, it is desirable for the copolymers to have a very low density—such as below 0.91 g/cc, below 0.90 g/cc, below 0.89 g/cc, and so forth—and these copolymers often are referred to a plastomers and/or elastomers. Ziegler-Natta catalyst systems can produce plastomers and elastomers, but metallocene-based catalyst systems can offer advantages in many important physical properties of these low density ethylene copolymers. Accordingly, the present invention is generally directed to the use of metallocene-based catalyst systems in a variety of polymerization processes to produce ethylene-based plastomers and elastomers.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify required or essential features of the claimed subject matter. Nor is this summary intended to be used to limit the scope of the claimed subject matter.

Polymerization processes for producing ethylene-based plastomers and elastomers are disclosed and described herein. In one aspect, for instance, a slurry polymerization process for producing an ethylene polymer having a density of less than or equal to about 0.91 g/cm3is disclosed, and in this aspect, the process can comprise contacting a catalyst composition with ethylene and an α-olefin comonomer in a diluent in a slurry reactor at a polymerization temperature in a range from about 50° C. to about 78° C. to produce the ethylene polymer. The catalyst composition can comprise a metallocene compound, a chemically-treated solid oxide, and optionally, a co-catalyst. The metallocene compound can be a single atom bridged or two atom bridged (two atom chain) metallocene compound, and the metallocene compound can be characterized by a comonomer incorporation efficiency of at least about 1% at the polymerization temperature (for the α-olefin comonomer).

In another aspect, a solution polymerization process for producing an ethylene polymer having a density of less than or equal to about 0.91 g/cm3is provided, and in this aspect, the process can comprise contacting a catalyst composition with ethylene and an α-olefin comonomer in a hydrocarbon solvent in a solution reactor at a polymerization temperature in a range from about 120° C. to about 160° C. (often, for an average residence time in a range from about 5 to about 90 min) to produce the ethylene polymer. The catalyst composition can comprise a metallocene compound, a chemically-treated solid oxide, and optionally, a co-catalyst, and the metallocene compound can be characterized by a comonomer incorporation efficiency of at least about 10% at the polymerization temperature.

In yet another aspect, a gas phase polymerization process for producing an ethylene polymer having a density of less than or equal to about 0.91 g/cm3is provided, and in this aspect, the process can comprise contacting a catalyst composition with ethylene and an α-olefin comonomer in a gas phase reactor containing an inert gas and a C4-C8alkane (a condensable agent) at a polymerization temperature in a range from about 48° C. to about 82° C. to produce the ethylene polymer. The catalyst composition can comprise a metallocene compound, a chemically-treated solid oxide, and optionally, a co-catalyst. In the gas phase reactor, the ratio of heavy hydrocarbon partial pressure to vapor pressure (ratio of P/P*) can be less than or equal to about 0.95.

The present invention also encompasses ethylene-based plastomers and elastomers. In some aspects, the ethylene polymer can be characterized by a density of less than or equal to about 0.91 g/cm3, a CY-a parameter of less than or equal to about 0.2, and a ratio of HLMI/MI of at least about 30, while in other aspects, the ethylene polymer can be characterized by a density of less than or equal to about 0.91 g/cm3, a CY-a parameter in a range from about 0.25 to about 0.75, and a ratio of Mw/Mn in a range from about 2 to about 3.

Both the foregoing summary and the following detailed description provide examples and are explanatory only. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Further, features or variations may be provided in addition to those set forth herein. For example, certain aspects and embodiments may be directed to various feature combinations and sub-combinations described in the detailed description.

