Asymmetric Metallocene Catalysts for High Molecular Weight Polypropylene
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Solution Overview
Problem
Existing metallocene catalysts for polypropylene production often result in reduced molecular weight during ethylene incorporation, and their productivity needs improvement, with existing asymmetric catalysts having poor activity and requiring complex, expensive synthesis processes.
Innovation Solution
Development of asymmetrical, chiral, racemic, anti-bridged bisindenyl metallocene catalysts with specific indenyl ligand substitution patterns, allowing for high molecular weight polypropylene production with improved catalyst productivity and reduced chain transfer to ethylene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If existing metallocene catalysts are used for propylene copolymerization with ethylene, then copolymer production is achieved, but molecular weight is strongly reduced
Solution Approach 1:
The patent employs asymmetrical bisindenyl metallocene catalysts where the two indenyl ligands are different from each other, with specific substitution patterns (one ligand with 2,4,7-trimethyl substitution and the other with 2,4,6-trimethyl substitution). This asymmetry creates a chiral environment that reduces chain transfer to ethylene while maintaining copolymerization activity, thereby preserving high molecular weight in the copolymer product.
2Quantity of substance
If existing metallocene catalysts are used to increase molecular weight, then higher molecular weights are obtained, but catalyst activity is reduced
Solution Approach 1:
The patent optimizes specific parameters of the metallocene structure including the bridge type (dimethylsilanediyl, diethylsilanediyl, or ethane-1,2-diyl), the substitution patterns on indenyl ligands, and the stereochemistry (rac-anti configuration). These parameter changes create a catalyst system that maintains high activity while producing high molecular weight polypropylene and copolymers, resolving the trade-off between molecular weight and catalyst activity.
3Productivity
If asymmetrical metallocene catalysts are designed to improve performance, then productivity and molecular weight are enhanced, but synthesis complexity and cost increase
Solution Approach 1:
The patent divides the complex asymmetrical metallocene catalyst into standardized modular components: a bridge unit (dimethylsilanediyl, diethylsilanediyl, or ethane-1,2-diyl), indenyl ligand frameworks, and substitution groups. These modules can be synthesized independently and assembled systematically, reducing overall synthesis complexity while maintaining the performance benefits of asymmetry.
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 catalysts achieve high molecular weight polypropylene with enhanced productivity and activity, producing isotactic polypropylene with melting temperatures above 150°C and high molecular weights, while simplifying the synthesis and reducing costs.
Implementation Method 1
asymmetric metallocene catalysts for the production of high molecular weight polypropylene homopolymers, and copolymers of propylene with ethylene
Implementation Method 2
Metallocene catalysts have been used to manufacture polyolefins for many years. Countless academic and patent publications describe the use of these catalysts in olefin polymerisation
Data Source
AI summary
An asymmetric complex of formula (I) wherein M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-SiR'2-, -R'2Ge-, wherein each R' is independently a hydrogen atom, C1-C20-alkyl, tri(C1-C20-alkyl)silyl, C6-C20-aryl, C7-C20-arylalkyl or C7-C20-alkylaryl; R2 and R2' are each independently a C1-C20 hydrocarbyl radical; R5' is a C1-20 hydrocarbyl group; R5 is hydrogen, or a C1-20 hydrocarbyl group; R6 is a non tertiary C1-10 alkyl group or C6-10-aryl group or C7-10 arylalkyl group or ZR3; R6' is a tertiary C4-20 alkyl group; R3 is a C1-20 hydrocarbyl group optionally substituted with halo; Ar is an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R1; Ar' is an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R1; each R1 is a C1-20 hydrocarbyl group or two R1 groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered ring with the Ar group, said ring being itself optionally substituted with one or more groups R4; and each R4 is a C1-20 hydrocarbyl group.