Hafnocene Catalyst System for High-Temperature Ethylene Copolymerization
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Solution Overview
Problem
Current metallocene catalyst systems for ethylene copolymerization lack high productivity combined with high solubility, molecular weight capability, and comonomer incorporation ability, especially at high temperatures, which are essential for producing ethylene copolymers with desired properties.
Innovation Solution
A new catalyst system comprising a metallocene complex with a specifically substituted bridged hafnocene or zirconium complex, combined with a boron-based cocatalyst, is used for high-temperature solution polymerization, enabling efficient ethylene copolymerization with high productivity, solubility, and comonomer incorporation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional metallocene catalyst systems are used for ethylene copolymerization at high temperatures, then polymerization can proceed at elevated temperatures, but productivity decreases and molecular weight capability is limited
Solution Approach 1:
The patent modifies the metallocene catalyst structure by introducing specific substituents (aromatic fused-ring groups, alkyl groups) at defined positions on the cyclopentadienyl and fluorenyl ligands. These structural parameter changes optimize the catalyst's electronic and steric properties, enabling it to maintain high productivity at elevated polymerization temperatures (above 100°C) while preserving molecular weight capability
2Productivity
If conventional metallocene catalyst systems are used for ethylene copolymerization, then polymerization can proceed, but comonomer incorporation ability is insufficient
Solution Approach 1:
The patent introduces specific substituents at particular positions (2,7-positions of fluorenyl ligand, 4,5-positions of cyclopentadienyl ligand) to create localized electronic and steric environments that enhance comonomer incorporation. The asymmetric substitution pattern creates distinct local qualities that favor comonomer insertion while maintaining ethylene polymerization activity
3Quantity of substance
If conventional metallocene catalyst systems are used, then catalyst can be employed, but solubility in polymerization medium is limited
Solution Approach 1:
The patent creates a composite catalyst structure by combining the metallocene core with specifically designed organic ligands containing aromatic fused-ring systems and alkyl substituents. This composite structure integrates solubility-enhancing moieties (alkyl groups, aromatic systems) with the catalytically active metallocene center, achieving high solubility in hydrocarbon solvents while maintaining catalytic functionality
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The new catalyst system achieves high productivity, solubility, and molecular weight capability, allowing for the production of ethylene copolymers with desired properties, such as low melt index and high comonomer incorporation, even at elevated temperatures.
Implementation Method 1
a catalyst system comprising a metallocene complex of formula (I)... along with a boron based cocatalyst... for producing polyethylene copolymers
Data Source
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AI summary
Catalyst system for producing ethylene copolymers in a high temperature solution process, the catalyst system comprising (i) a metallocene complex of formula (I) wherein: M is Hf or a mixture with Zr, provided that more than 50% by moles of the complex of Formula (I) has M = Hf; X is a sigma ligand; R are the same or different from each other and can be saturated linear or branched C1-C10 alkyl, C6-C10 aryl, C4-C10 heteroaryl, C6-C20 alkylaryl or C6-C20 arylalkyl groups, which can optionally contain up to 2 heteroatoms or silicon atoms; R1 is a C6-C10 aryl or C6-C20 alkylaryl group optionally containing up to 2 heteroatoms or silicon atoms or a C4-C10 heteroaryl group; R2 is a C4-C20 cycloalkyl group, optionally carrying alkyl substituents in beta-positions, of formula (II) in which R' can be the same or can be different from each other and can be hydrogen or is defined as R and n is 1 to 17 (ii) a boron containing cocatalyst