Olefin polymerization process
View Patent ↗A slurry process for polymerizing ethylene is disclosed. The process comprises polymerizing ethylene in a first reactor in the presence of hydrogen and a catalyst comprising an activator and a supported dimethylsilyl-bridged indeno[1,2-b]indolyl zirconium complex to produce an ethylene homopolymer, removing some of the unreacted hydrogen, and reacting the homopolymer slurry in a second reactor with ethylene and a C 3 -C 10 α-olefin to produce polyethylene. The polyethylene has weight-average molecular weight greater than 150,000, broad molecular weight distribution, low long-chain branching, and it provides pipes or molded articles with good environmental stress crack resistance.
1. A slurry process for making polyethylene useful in pipe or molding applications and having low long-chain branching and broad molecular weight distribution, said process comprising:
(a) in a first reactor, polymerizing ethylene in the presence of hydrogen and a catalyst comprising an activator and a supported, dimethylsilyl-bridged indeno[1,2-b]indolyl zirconium complex to produce a slurry comprising an ethylene homopolymer having a weight-average molecular weight within the range of 15,000 and 150,000;
(b) removing at least some of the unreacted hydrogen from the slurry; and
(c) in a second reactor, reacting the slurry from step (b) with ethylene and a C 3 -C 10 α-olefin to produce polyethylene with a weight-average molecular weight greater than 150,000, an M w /M n greater than 20, and a viscosity enhancement factor of less than 2.0; wherein the complex has a structure selected from the group consisting of:
wherein each R 1 is independently a C 1 -C 10 hydrocarbyl; each R 2 is independently selected from the group consisting of H, F, and C l -C 10 hydrocarbyl; R 3 is a C 4 -C 10 hydrocarbyl; and each L is independently selected from the group consisting of halide, alkoxy, aryloxy, siloxy, alkylamino, and C 1 -C 30 hydrocarbyl.
2. The process of claim 1 wherein the ethylene homopolymer has a weight-average molecular weight within the range of 25,000 and 50,000.
3. The process of claim 1 wherein the polymerization in each of the first and second reactors is performed at a temperature within the range of 40° C. to 90° C.
4. The process of claim 1 wherein the polyethylene has a density within the range of 0.945 and 0.955 g/cm 3 .
5. The process of claim 1 wherein each of R 1 and R 2 is methyl.
6. The process of claim 5 wherein R 3 is n-butyl.
7. The process of claim 1 wherein the catalyst comprises an activator and a supported, dimethylsilyl-bridged indeno[1,2-b]indolyl zirconium complex in combination with a second supported single-site complex.
8. The process of claim 1 wherein the complex is a mixture of diastereomers.
9. The process of claim 1 wherein the complex has the structure:
wherein each R 1 is independently a C 1 -C 10 hydrocarbyl; each R 2 is independently selected from the group consisting of H, F, and C 1 -C 10 hydrocarbyl; R 3 is a C 4 -C 10 hydrocarbyl; and each L is independently selected from the group consisting of halide, alkoxy, aryloxy, siloxy, alkylamino, and C 1 -C 30 hydrocarbyl and the molar ratio of rac1:rac2 stereoisomers in the complex is from 0.1:1 to 1:0.1.
10. The process of claim 1 wherein the complex has the structure:
wherein each R 1 is independently a C 1 -C 10 hydrocarbyl; each R 2 is independently selected from the group consisting of H, F, and C 1 -C 10 hydrocarbyl; and each L is independently selected from the group consisting of halide, alkoxy, aryloxy, siloxy, alkylamino, and C 1 -C 30 hydrocarbyl and the molar ratio of rac:meso stereoisomers in the complex is from 0.1:1 to 1:0.1.