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Bullvalene "Ball Joint" Fluxionality Modulates Mechanics and Dynamic Fragility in Polymer Glass.
Peiguan B Sun1, Matthew R Golder1
1Department of Chemistry and Molecular Engineering & Science Institute, University of Washington, 3790 Okanogan Ln, Seattle, Washington 98195, United States.
ACS Polymers Au
|October 13, 2025
Summary
Researchers introduced molecular fluxionality using bullvalene to create stronger polymer glasses. This novel approach reduces material fragility, enhancing predictable performance in practical temperature ranges.
Area of Science:
- Materials Science
- Polymer Chemistry
- Physical Chemistry
Background:
- Dynamic fragility quantifies viscosity changes during polymer glass transition.
- Material fragility impacts service temperature windows and predictable mechanical properties.
- Polymer chain flexibility typically governs fragility by balancing relaxation and segmental motion.
Purpose of the Study:
- To introduce molecular fluxionality as a novel motif for controlling polymer glass fragility.
- To investigate the use of bullvalene Hardy-Cope rearrangements in poly(methyl methacrylate) networks.
- To assess the impact of molecular rearrangements on glass strength and transition behavior.
Main Methods:
- Synthesizing poly(methyl methacrylate) thermosets cross-linked with bullvalene.
- Comparing fragility of bullvalene-cross-linked networks with static adamantane-derived controls.
- Analyzing the effect of sigmatropic rearrangements on local molecular motion and glass properties.
Main Results:
- Bullvalene-cross-linked thermosets exhibited significantly lower dynamic fragility compared to controls.
- Materials demonstrated enhanced glass strength due to molecular fluxionality.
- Sigmatropic rearrangements within the bullvalene cage influenced glass formation.
Conclusions:
- Molecular fluxionality, via bullvalene rearrangements, effectively reduces polymer glass fragility.
- This approach offers a new strategy for designing stronger polymer glasses with improved thermal stability.
- Understanding local molecular motion is key to controlling glass transition dynamics and material applications.
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