Tightly-Bridged Metallocene Catalysts for Low Melt Elasticity
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Solution Overview
Problem
Metallocene catalyst systems often produce polyethylene with high melt elasticity, leading to undesirable film properties such as anisotropic properties, melt fracturing, and surface haze, while striving for high molecular weight resins with low melt elasticity remains a challenge.
Innovation Solution
A catalyst composition comprising a tightly-bridged ansa-metallocene compound with an alkyl group substituent on cyclopentadienyl-type ligands, combined with a support and/or activator-support, and optionally an organoaluminum compound, is used to polymerize olefins, allowing for the production of high molecular weight resins with low melt elasticity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If metallocene catalyst systems are used to produce polyethylene, then high molecular weight resins can be obtained, but melt elasticity becomes high leading to undesirable film properties
Solution Approach 1:
The patent applies local quality by introducing specific substituents (alkyl, aryl, alkoxyl, aryloxy groups) at particular positions on the cyclopentadienyl rings of the metallocene catalyst. These localized chemical modifications at specific sites create asymmetric steric environments that control monomer insertion geometry, thereby reducing melt elasticity while maintaining high molecular weight polymer production.
Solution Approach 2:
The patent changes chemical parameters of the metallocene catalyst by substituting hydrogen atoms with various organic groups (methyl, ethyl, propyl, butyl, phenyl, etc.) at specific positions on the cyclopentadienyl rings. These parameter changes in catalyst structure directly influence the polymer's melt elasticity and molecular weight characteristics, resolving the contradiction between high molecular weight and low melt elasticity.
2Quantity of substance
If metallocene catalyst systems are used to produce polyethylene, then high molecular weight resins can be obtained, but film properties such as anisotropic properties, melt fracturing, and surface haze occur
Solution Approach 1:
The patent introduces specific local substitutions on the cyclopentadienyl rings at defined positions (using formulas I and II) to create asymmetric steric environments. This local structural modification controls the polymerization geometry, producing polymers with improved film properties including reduced anisotropy, minimized melt fracturing, and decreased surface haze while maintaining high molecular weight.
Solution Approach 2:
The patent employs asymmetric substitution patterns on the cyclopentadienyl rings where substituents are placed at specific non-equivalent positions (e.g., positions 1, 2, 3, 4, 5, 6 with selective substitution). This asymmetry in catalyst structure creates chiral or prochiral environments that control monomer insertion, leading to polymers with superior film formation characteristics and reduced manufacturing defects.
3Productivity
If conventional catalyst systems are used, then polymerization can proceed, but comonomer incorporation is insufficient
Solution Approach 1:
The patent changes the chemical parameters of the metallocene catalyst by introducing electron-donating or electron-withdrawing substituents (alkyl, aryl, alkoxyl, aryloxy groups) at specific positions on the cyclopentadienyl rings. These parameter changes modify the electronic density at the metal center, enhancing its ability to coordinate and incorporate comonomers (such as 1-hexene, 1-octene, ethylidene) while maintaining reliable polymerization efficiency 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 catalyst composition effectively reduces melt elasticity, improving film properties by enhancing comonomer incorporation and processing capabilities, resulting in polymers with improved tear strength and reduced surface irregularities.
Implementation Method 1
catalyst composition comprising a tightly-bridged ansa-metallocene compound... combined with a support and/or activator-support... used to polymerize olefins
Data Source
AI summary
The present techniques relate to catalyst compositions, methods, and polymers encompassing a Group 4 metallocene compound comprising bridging η5-cyclopentadienyl-type ligands, typically in combination with a cocatalyst, and a activator. The compositions and methods presented herein include ethylene polymers with low melt elasticity.