Ruthenium Catalysts for Nitrile Rubber Metathesis
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Solution Overview
Problem
Current metathesis catalysts for nitrile rubber are unsatisfactory for certain applications, particularly in terms of stability and activity, leading to suboptimal metathesis reactions with nitrile rubber, which limits their effectiveness in reducing molecular weight and improving processability.
Innovation Solution
The use of specific ruthenium-based catalysts of the general formula (I), particularly (I.A), (I.B), and (I.C), which exhibit higher metathesis activity and prevent gel formation during the metathesis degradation of nitrile rubber, allowing for efficient molecular weight reduction without noticeable gel formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional metathesis catalysts (Grubbs II, Hoveyda-Grubbs II) are used for nitrile rubber degradation, then some metathesis activity is achieved, but the catalyst stability and activity are insufficient, leading to suboptimal molecular weight reduction
Solution Approach 1:
The patent modifies the catalyst structure by changing the ligand parameters - specifically using N-heterocyclic carbene ligands with electron-withdrawing groups (trifluoromethyl, cyano, or nitro substituents) at the 4-position of the imidazolium ring. This parameter change in the ligand electronics optimizes the catalyst's metathesis activity and stability for nitrile rubber degradation, resolving the contradiction between productivity and reliability.
2Ease of operation
If metathesis reaction is performed to reduce molecular weight of nitrile rubber, then processability is improved, but gel formation occurs which compromises the degradation quality
Solution Approach 1:
The patent converts the potential harmful gel formation side reaction into a beneficial outcome by designing a catalyst that promotes complete metathesis degradation. The specialized NHC-ligated ruthenium catalyst ensures thorough chain scission of the nitrile rubber, preventing gel formation by maintaining controlled reaction conditions that favor complete degradation over side reactions.
3Productivity
If existing catalysts are used for metathesis of nitrile rubber, then some degradation occurs, but the metathesis activity is not high enough for efficient molecular weight reduction
Solution Approach 1:
The patent achieves high metathesis activity by modifying the electronic parameters of the N-heterocyclic carbene ligand. The introduction of electron-withdrawing groups (CF3, CN, or NO2) at the 4-position optimizes the electron density at the ruthenium center, enhancing its ability to activate and cleave the nitrile rubber chains. This parameter optimization dramatically increases metathesis activity, reducing the time required for efficient molecular weight reduction.
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
These catalysts achieve significant reduction in molecular weight and polydispersity index, enhancing the processability of nitrile rubber while maintaining high metathesis activity, outperforming existing catalysts like Grubbs II and Hoveyda-Grubbs II in metathesis degradation without gel formation.
Implementation Method 1
Olefin metathesis (hereinafter also referred to as metathesis degradation or metathesis reaction) is a reaction for reducing the molecular weight with huge economic importance.
Implementation Method 2
The use of specific ruthenium-based catalysts of the general formula (I), particularly (I.A), (I.B), and (I.C), which exhibit higher metathesis activity
Data Source
AI summary
The present invention relates to the use of specific catalysts for the metathesis degradation of nitrile rubber (NBR). The invention further relates to a method for preparing nitrile rubber with reduced molecular weight using specific catalysts.