Processes of controlling molecular weight distribution in ethylene/alpha-olefin compositions
The present invention relates to compositions and processes of making polymers having a controlled molecular weight distribution. The molecular weight distribution is controlled, for example, by controlling the relative monomer concentrations during contact with a pre-catalyst and/or using a catalyst comprising a catalytic amount of a molecule having the structure: wherein M=group 2-8 metal, preferably group 4 as a neutral or charged moiety; Y=any substituent including fused rings; L=any ligating group, especially a pyridyl or pyridylamide; X=alkyl, aryl, substituted alkyl, H or hydride, halide, or other anionic moiety; y=an integer from 0 to the complete valence of M; R=alkyl, aryl, haloalkyl, haloaryl, hydrogen, etc; x=1-6, especially 2; Dashed line=optional bond, especially a weak bond; and X and (CR 2 ) x may be tethered or part of a ring.
1. A process for producing an ethylene/α-olefin interpolymer composition comprising:
(a) selecting a single suitable pre-catalyst comprising at least one metal-aryl or metal-hydrocarbyl bond, wherein each pre-catalyst molecule is essentially the same as every other pre-catalyst molecule;
(b) contacting a concentration of ethylene and an α-olefin with said suitable pre-catalyst, the concentration comprising an α-olefin mole fraction, f 2 , defined as
f
2
=
[
α
-
olefin
]
∑
[
ethylene
+
α
-
olefin
]
;
(c) activating the pre-catalyst to produce an ethylene-inserted cation and an α-olefin-inserted cation;
(d) forming, with the cations, under continuous reaction polymerization conditions an ethylene/α-olefin interpolymer composition with a bimodal molecular weight distribution and comprising a high molecular weight component and a low molecular weight component; and
(e) controlling the amount of high molecular weight component by controlling the value of f2.
2. The process of claim 1 which further comprises employing a pre-catalyst comprising a ligand and terminating the reaction conditions via a catalyst quench.
3. The process of claim 2 wherein a ligand fragment with an appended olefin can be detected from the catalyst quenchate.
4. The process of claim 1 wherein the reaction conditions comprise at least one cocatalyst differing from the pre-catalyst.
5. The process of claim 1 wherein the suitable pre-catalyst is selected from the group consisting of hydrocarbylamine substituted heteroaryl compounds corresponding to the formula:
wherein:
R 11 is selected from alkyl, cycloalkyl, heteroalkyl, cycloheteroalkyl, aryl, and inertly substituted derivatives thereof containing from 1 to 30 atoms not counting hydrogen or a divalent derivative thereof;
T 1 is a divalent bridging group of from 1 to 41 atoms other than hydrogen;
R 12 is a C 5-20 heteroaryl group containing Lewis base functionality;
M 1 comprises hafnium or other Group 4 metal;
X 1 is an anionic, neutral or dianionic ligand group;
x′ is a number from 0 to 5 indicating the number of such X 1 groups; and bonds, optional bonds and electron donative interactions are represented by lines, dotted lines and arrows respectively, in contact with a co-catalyst.
6. The process of claim 1 wherein the ethylene/α-olefin interpolymer composition is produced in a single polymerization reactor.
7. The process of claim 1 wherein the ethylene/α-olefin interpolymer composition is produced using N-(2,6-di(1-methylethyl)phenyl)amido)(2-isopropylphenyl)(α-naphthalen-2-diyl(6-pyridin-2-diyl)methane)]hafnium dimethyl.
8. A process for producing an ethylene/α-olefin interpolymer composition comprising:
(a) selecting a single pre-catalyst comprising at least one metal-aryl or metal-hydrocarbyl bond, wherein each pre-catalyst molecule is essentially the same as every other pre-catalyst molecule;
(b) contacting the pre-catalyst with ethylene and at least one α-olefin monomer;
(c) changing, with the contacting, the ligand structure of the pre-catalyst and forming a catalyst mixture comprising (i) an ethylene-inserted cation and (ii) an alpha olefin-inserted cation;
(d) forming, with the cations, an ethylene/α-olefin interpolymer composition with a bimodal molecular weight distribution under continuous reaction polymerization conditions, the ethylene/α-olefin interpolymer having a low molecular weight component formed by the ethylene-inserted cation and a high molecular weight component formed by the alpha olefin-inserted cation.
9. The process of claim 8 comprising combining the pre-catalyst with a member selected from the group consisting of a mixture of ketones, a cocatalyst, a shuttling agent, and combinations thereof.
10. The process of claim 8 comprising controlling the amount of low molecular weight component and the amount of high molecular weight component by controlling the relative amounts the ethylene-inserted cation and the alpha olefin-inserted cation.
11. The process of claim 8 comprising
controlling the concentration of ethylene and α-olefin contacted with the pre-catalyst such that the mole fraction f 2 , is defined as
f
2
=
[
α
-
olefin
]
∑
[
ethylene
+
α
-
olefin
]
.
12. The process of claim 5 wherein R 12 comprises a pyridin-2-yl- or substituted pyridin-2-yl group or a divalent derivative thereof.
13. The process of claim 8 wherein the pre-catalyst comprises hafnium.