Multimodal Polyisoolefin Composition for Green Strength and Processability
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Solution Overview
Problem
High molecular weight butyl rubbers exhibit improved green strength but negatively impact stress relaxation and processing characteristics, leading to challenges in the processability of polyisoolefin polymers, particularly in mixing, calendaring, extrusion, and molding, which existing modifications often address at the cost of physical properties or through additional synthesis steps.
Innovation Solution
A polyisoolefin-based polymer composition with a multimodal molecular weight distribution, featuring a low molecular weight fraction of less than 100,000 g/mol and a high molecular weight fraction of greater than 250,000 g/mol, achieved by polymerizing isoolefin in the absence and presence of a chain transfer agent, respectively, to enhance processability while maintaining physical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight butyl rubber is used to improve green strength, then green strength is improved, but stress relaxation and processing characteristics are negatively impacted
Solution Approach 1:
The patent segments the molecular weight distribution into multiple modes (typically bimodal or trimodal), combining high molecular weight fractions for green strength with low molecular weight fractions for processing. The high molecular weight fraction (Mw > 250,000 g/mol) provides green strength, while the low molecular weight fraction (Mw < 100,000 g/mol) improves stress relaxation and processing characteristics, resolving the contradiction between these properties.
Solution Approach 2:
The patent changes the molecular weight distribution parameters from a single peak to a multimodal distribution. By controlling the polymerization process to produce specific molecular weight fractions with defined peak molecular weights and relative amounts, the patent optimizes both green strength and processing characteristics simultaneously.
2Strength
If high molecular weight butyl rubber is used to improve green strength, then green strength is improved, but mixing time and energy increase
Solution Approach 1:
The patent segments the molecular weight distribution to include low molecular weight fractions that reduce viscosity and improve flow characteristics during mixing. The low molecular weight fraction (Mw < 100,000 g/mol) acts as an internal lubricant, reducing mixing time and energy requirements while the high molecular weight fraction (Mw > 250,000 g/mol) maintains green strength.
Solution Approach 2:
The patent changes the molecular weight distribution parameters to include a low molecular weight mode that reduces processing viscosity. This parameter change decreases the energy and time required for mixing operations while preserving the green strength through the high molecular weight fraction.
3Strength
If high molecular weight butyl rubber is used to improve green strength, then green strength is improved, but compounding costs increase
Solution Approach 1:
The patent segments the molecular weight distribution to optimize the balance between performance and cost. The low molecular weight fraction reduces compounding costs by improving processability and reducing mixing energy, while the high molecular weight fraction maintains the necessary green strength, achieving cost-effective manufacturing.
Solution Approach 2:
The patent changes the molecular weight distribution parameters to include low molecular weight fractions that reduce compounding costs through improved processing efficiency. This parameter optimization reduces energy consumption and manufacturing time, lowering overall compounding costs while maintaining green strength.
4Strength
If high molecular weight butyl rubber is used to improve green strength, then green strength is improved, but throughput production decreases
Solution Approach 1:
The patent segments the molecular weight distribution to include low molecular weight fractions that improve flow and processing characteristics. This segmentation enables higher throughput production by reducing viscosity and improving extrusion and molding rates, while the high molecular weight fraction maintains green strength.
Solution Approach 2:
The patent changes the molecular weight distribution parameters to include a low molecular weight mode that increases productivity. This parameter change reduces processing viscosity and improves flow characteristics, enabling higher throughput in extrusion and molding operations while preserving green strength through the high molecular weight fraction.
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 multimodal molecular weight distribution improves processability, reducing mixing time and energy, compounding costs, and enabling higher throughput production with reduced oil use and increased filler loading, while maintaining the physical stability and impermeability of cured articles.
Implementation Method 1
continuing to polymerize the isoolefin in a second step in the presence of a chain transfer agent to produce a polyisoolefin-based polymer composition comprising a multimodal molecular weight distribution
Data Source
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AI summary
A polyisoolefin-based polymer composition having a multimodal molecular weight distribution is described, which can be prepared by the late addition of a chain transfer agent to the polymerization process. The polymer composition has a low molecular weight fraction having a peak molecular weight (Mp) of less than about 100,000 g/mol and a high molecular weight fraction having a peak molecular weight (Mp) of greater than about 250,000 g/mol, the low molecular weight fraction present in the composition in an amount less than the high molecular weight fraction. Cured articles produced from the polyisoolefin-based polymer composition exhibit improved processability while maintaining physical properties.