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Transición de vidrio prolongada debido a restricciones topológicas en polirotaxanos
Kazuaki Kato1,2, Akihiro Ohara1, Hideaki Yokoyama1
1Department of Advanced Materials Science, Graduate School of Frontier Sciences , The University of Tokyo , 5-1-5 Kashiwanoha , Kashiwa , Chiba 277-8561 , Japan.
Journal of the American Chemical Society
|August 2, 2019
Resumen
Las restricciones topológicas en los polirotaxanos influyen en la dinámica de transición vítrea. El aumento de la cobertura del anillo prolonga la relajación mecánica, indicando el movimiento del segmento restringido más allá de la temperatura de transición de vidrio (Tg).
Área de la Ciencia:
- Ciencia de los Polímeros
- Ciencias de los materiales
- Química Física
Sus antecedentes:
- Los polirotaxanos son polímeros supramoleculares con estructuras topológicas únicas.
- La transición de vidrio (Tg) es una propiedad crítica que afecta la dinámica del polímero y el rendimiento del material.
- La comprensión de Tg en polirotaxanos es esencial para el diseño de materiales avanzados.
Objetivo del estudio:
- Investigar el impacto de las restricciones topológicas en la dinámica de transición vítrea de los polirotaxanos.
- Estudiar sistemáticamente cómo los diferentes grados de cobertura del anillo afectan el comportamiento de relajación.
- Para aclarar la relación entre el movimiento molecular y las restricciones topológicas.
Principales métodos:
- Síntesis de polirotaxanos con proporciones variables de moléculas de polímero y anillo roscado.
- Análisis térmico diferencial (DTA) para determinar las temperaturas de transición de vidrio (Tg).
- Medidas de relajación mecánica para analizar el comportamiento dinámico.
Principales resultados:
- Se observaron valores similares de Tg en diferentes polirotaxanos de cobertura a través del DTA.
- Los tiempos de relajación mecánica aumentaron significativamente con una mayor cobertura del anillo.
- Surgió un proceso de relajación en dos pasos, con un componente más lento dependiente de la cobertura.
- Se encontró que los movimientos segmentales se congelaban a temperaturas considerablemente más altas que Tg, aumentando con la cobertura.
Conclusiones:
- Las restricciones topológicas en los polirotaxanos alteran significativamente la dinámica de la transición al vidrio.
- Mientras que los anillos se liberan de las interacciones convencionales en Tg, su movimiento translacional cooperativo se ve obstaculizado por los polímeros roscados.
- El aumento de la cobertura del anillo conduce a movimientos segmentarios más restringidos a temperaturas más altas, lo que afecta las propiedades del material.
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