In Situ Isomerization of Polybutadiene for Low-Temperature Flexibility
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Solution Overview
Problem
High cis-1,4 content polybutadienes become rigid at low temperatures due to crystallization, making them unsuitable for cold climate tires, as they exhibit a high shear modulus which is not desirable for rubber compositions used in such environments.
Innovation Solution
In situ isomerization of polybutadiene by adding disulfide isomerization agents such as 2,2-dithiobis(benzothiazole) during the mixing and curing process, converting some cis-1,4 bonds to trans-1,4 bonds, thereby reducing the complex shear modulus at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high cis-1,4 content polybutadiene is used to improve wear performance, then wear resistance is improved, but the rubber becomes rigid at low temperatures due to crystallization
Solution Approach 1:
The patent changes the microstructural parameters of polybutadiene by controlling the cis-1,4 bond content through catalyst selection (neodymium vs lithium) and applying isomerization treatment to reduce crystallinity. This allows maintaining wear resistance while improving low-temperature flexibility by adjusting the molecular structure parameters
Solution Approach 2:
The patent creates a composite rubber composition combining polybutadiene with other elastomers (such as polyisoprene, poly(styrene-butadiene copolymer), or poly(isoprene-styrene copolymer)) to achieve synergistic effects where the composite maintains wear resistance while the additional components prevent excessive crystallization at low temperatures
2Strength
If high cis-1,4 content polybutadiene is used to improve wear performance, then wear resistance is improved, but the complex shear modulus becomes too high at low temperatures
Solution Approach 1:
The patent applies isomerization treatment to change the geometric configuration of double bonds from cis-1,4 to trans-1,4 or vinyl-1,2 structures, thereby reducing the regularity and crystallinity of the polymer chains. This parameter change in molecular structure directly reduces the complex shear modulus at low temperatures while preserving wear resistance properties
3Strength
If polybutadiene with high regularity of structure is used, then wear performance is improved, but crystallization occurs at low temperatures causing stiffening
Solution Approach 1:
The patent introduces isomerization as a post-polymerization treatment to change the stereochemical parameters of the polybutadiene structure. By converting some cis-1,4 bonds to other configurations, the regularity parameter is reduced, preventing crystallization while maintaining the wear performance benefits of the original high-cis structure
Solution Approach 2:
The patent applies isomerization treatment during the rubber compounding process before final product formation. This preliminary action modifies the molecular structure in advance to prevent crystallization issues that would occur during subsequent storage and use in cold climates
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 in situ isomerization process results in a rubber composition with a suitable complex shear modulus at low temperatures, preventing the stiffening of polybutadiene, thus enhancing its performance in cold climate tires without compromising its properties.
Implementation Method 1
adding at least 3 phr of a disulfide isomerization agent and mixing the disulfide isomerization agent with the mixture components
Data Source
AI summary
Methods for in situ isomerization if polybutadiene may include adding mixture components of the cross-linkable rubber composition into a mixer, the mixture components comprising at least 10 phr of a polybutadiene rubber having at least 80 wt % cis-bonds and up to 90 phr of a second rubber component having at least some dienic unsaturation and mixing the mixture components during a nonproductive phase. Such methods may include processing the mixture components on a mill during a productive phase, adding at least 3 phr of a disulfide isomerization agent and mixing the disulfide isomerization agent with the mixture components. The mixing may take place in an internal mixer with the isomerization agent added to the mixer or alternatively, it may be added to the mill after the mixture components have been dropped from the mixer for cooling on the mill.