Ans-Metallocene Catalyst for High Molecular Weight Polyolefins
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Solution Overview
Problem
Traditional metallocene catalysts produce polymers with wide molecular weight distribution and uneven comonomer composition, limiting the control over polymer properties such as stereoregularity, crystallinity, and molecular weight.
Innovation Solution
A novel ansa-metallocene compound with indenyl ligands and a Lewis base functional group as a bridge, preventing meso-form formation and enhancing catalytic activity, is used as a catalyst for olefin polymerization, either alone or supported on silica, to produce polyolefins with controlled microstructure and high molecular weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional Ziegler-Natta catalyst is used for olefin polymerization, then high productivity is achieved, but the molecular weight distribution of the polymer becomes wide and comonomer composition becomes uneven
Solution Approach 1:
The invention changes the fundamental parameter of catalyst structure from multi-site Ziegler-Natta to single-site metallocene, which fundamentally alters the polymerization mechanism to achieve narrow molecular weight distribution while maintaining high activity through optimized ligand design
Solution Approach 2:
The invention uses a composite ansa-metallocene structure combining indenyl ligands with a cyclopentadienyl-fluorenyl bridge, creating a single-site catalyst that provides both high activity and precise molecular weight control through its unique electronic and steric properties
2Productivity
If ansa-metallocene catalyst with bis-indenyl ligand is used, then catalytic activity is enhanced, but both racemate and meso diastereomers are simultaneously formed with the meso form being undesirable
Solution Approach 1:
The invention introduces asymmetry through the chiral ansa-bridge structure that creates a rigid, asymmetric environment around the metal center, favoring the formation of the racemate diastereomer which produces isotactic polymers, while the asymmetric steric arrangement prevents meso diastereomer formation
Solution Approach 2:
The invention modifies the local steric environment at the ligand-metall center interface by using bulky substituents on the indenyl ligands, creating localized steric hindrance that directs the approach of monomers and controls the stereochemistry of polymerization to favor racemate formation
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 novel metallocene compound achieves high catalytic activity and controlled microstructure of polyolefins, producing polymers with improved stereoregularity, crystallinity, and molecular weight distribution, particularly enabling the preparation of high molecular weight polyolefins with enhanced mechanical strength and crystallinity.
Implementation Method 1
the bridge group connecting the ligands is substituted with the functional group which can take a role of Lewis base as an oxygen-donor
Implementation Method 2
A novel ansa-metallocene compound with indenyl ligands and a Lewis base functional group as a bridge, preventing meso-form formation and enhancing catalytic activity, is used as a catalyst for olefin polymerization
Data Source
AI summary
The present invention relates to a metallocene compound having novel structure which can provide various selectivity and activity to polyolefin copolymers, a preparation method thereof, and a preparation method of polyolefin using the metallocene compound.