Sulfur-Tethered Metallocene Catalysts for Low-LCB Polyethylene
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in advancing metallocene-based catalysts is the control of long chain branching (LCB), which affects polymer processing and resin properties, necessitating new catalysts and processes that can reduce or control LCB.
Innovation Solution
Incorporating sulfur-containing pendent groups into metallocene structures, such as bridged metallocenes with carbon-bridged fluorenyl and cyclopentadienyl ligands bearing an alkylsulfide group, to inhibit LCB formation during olefin polymerization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a polar heteroatom group (such as sulfur-containing pendent groups) is incorporated into the metallocene structure to inhibit LCB formation, then LCB formation is reduced, but the catalyst activity may be deactivated due to the cationic and highly electrophilic nature of the heteroatom
Solution Approach 1:
The patent introduces a sulfur-containing pendent group as an intermediary element that coordinates to the metallocene center, acting as a mediator between the catalyst and the polymerization process. This sulfur group selectively interacts with the catalytic site to prevent macromonomer insertion while maintaining overall catalyst functionality, thus reducing LCB without completely deactivating the catalyst.
Solution Approach 2:
The patent modifies the chemical environment of the metallocene center by changing the electronic parameters through sulfur substitution. The sulfur-containing pendent group alters the electron density and electrophilicity at the catalytic site, creating a new parameter state that selectively inhibits LCB formation while preserving polymerization activity through controlled electronic effects.
2Object-generated harmful factors
If a tethered olefin group is incorporated into the metallocene structure to reduce LCB formation, then LCB is reduced, but the catalyst activity is slightly decreased compared to unsubstituted alkyl-tethered metallocenes
Solution Approach 1:
The patent changes the chemical parameter of the tether group from unsubstituted alkyl to sulfur-containing substituent. This parameter change modifies the electronic and steric properties at the metallocene center, creating a new balance between LCB inhibition and catalyst activity that is slightly less active than unsubstituted analogs but significantly reduces LCB.
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 sulfur-containing pendent groups effectively reduce LCB formation, maintaining high polymerization activity and producing polyethylene with low LCB levels, comparable to tethered olefin groups while being slightly less active than unsubstituted alkyl-tethered metallocenes.
Implementation Method 1
the pendent olefin may protect the active catalytic site by coordinating the metallocene and in doing so, inhibit the insertion of an in-situ generated macromonomer or olefin oligomer into a growing polymer chain
Implementation Method 2
catalyst compositions for producing ethylene homopolymers and co-polymers, and polymerization processes for preparing the same
Data Source
AI summary
Disclosed are metallocene compounds, catalyst compositions and methods for making catalyst compositions, and processes for polymerizing olefins. In an aspect, a series of cyclopentadienyl tert-butyl fluorenyl metallocenes featuring various alkylsulfide groups on a carbon bridge linking the cyclopentadienyl tert-butyl fluorenyl ligands were prepared and evaluated as ethylene polymerization catalysts in the presence of metallocene activators, such as solid super acids (SSA). The metallocenes containing these tethered alkylsulfide substituents provide catalysts which exhibited excellent ethylene polymerization activities comparable to the analogous metallocenes containing tethered olefins and polyethylenes with reduced long chain branching (LCB) relative to metallocenes with a saturated hydrocarbyl tether.