Indacene Metallocene Catalysts for Propylene Polymerization
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Solution Overview
Problem
Current metallocene catalysts for olefin polymerization face limitations in producing high molecular weight propylene-ethylene copolymers and isotactic polypropylene with desired properties, particularly at higher temperatures, due to issues with β-hydrogen transfer and catalyst activity.
Innovation Solution
Development of novel catalyst compounds and systems featuring a transition metal compound with a 1,5,6,7-tetrahydro-s-indacenyl moiety bridged to another indacenyl or indenyl moiety, combined with a non-coordinating anion activator, for polymerizing propylene and optional olefin comonomers at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional metallocene catalysts are used for propylene polymerization, then catalyst activity is maintained at acceptable levels, but molecular weight of propylene-ethylene copolymers remains low due to β-hydrogen transfer to ethylene comonomer
Solution Approach 1:
The patent introduces a 2-methyl substitution at a specific local position on the indenyl ligand, creating a localized steric effect that selectively prevents β-hydrogen transfer to ethylene comonomer while maintaining overall catalyst activity and propylene polymerization efficiency
Solution Approach 2:
The catalyst system employs asymmetric substitution patterns on the indenyl ligands (e.g., 2-methyl-4-phenylindenyl), creating chiral environments that control stereospecificity and prevent unwanted β-hydrogen transfer reactions
2Productivity
If metallocene catalysts operate at higher temperatures to increase productivity, then reactor throughput improves, but polymer molecular weight decreases due to enhanced β-hydrogen transfer
Solution Approach 1:
The patent modifies the catalyst's structural parameters (adding methyl substitution at 2-position of indenyl ligand) to change its temperature-dependent behavior, allowing the catalyst to maintain high molecular weight polymer production even at elevated operating temperatures
3Quantity of substance
If 2-Me substitution is introduced to suppress β-hydrogen transfer to propylene, then homopolymer molecular weight increases, but activity and productivity decrease
Solution Approach 1:
The patent places the methyl substitution at a specific local position (2-position) on the indenyl ligand, creating a localized steric barrier that selectively affects β-hydrogen transfer to ethylene while preserving the overall catalytic activity for propylene polymerization
Solution Approach 2:
The catalyst system combines multiple structural features (indenyl ligands with specific substituents, metal center, and supporting framework) to create a composite catalytic system where the methyl substitution works synergistically with other structural elements to balance molecular weight control and activity
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 enables the production of propylene-ethylene copolymers with improved molecular weight and MFR, allowing for higher temperature polymerization without compromising polymer properties, thereby enhancing reactor throughput and reducing operating costs.
Implementation Method 1
catalyst systems comprising a transition metal compound... for polymerizing propylene and optional olefin comonomers
Data Source
AI summary
This invention relates homogeneous (typically solution) polymerization of propylene and optional olefin comonomer using metallocene catalyst compounds having a 1,5,6,7-tetrahydro-s-indacenyl moiety bridged to another indacenyl moiety or bridged to a substituted or unsubstituted indenyl moiety.