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Efectos de memoria dinámica en la mecanoquímica de los polímeros cíclicos
Yangju Lin1, Yudi Zhang1, Zi Wang1
1Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States.
Journal of the American Chemical Society
|July 9, 2019
Resumen
Los polímeros cíclicos con mecanóforos gem-diclorociclopropano muestran una activación reducida en comparación con los análogos lineales. Esto sugiere que los intermediarios de fragmentación retienen la memoria de su origen cíclico durante la escisión mecanoquímica.
Área de la Ciencia:
- Química de los polímeros
- Mecanoquímica
- Ciencias de los materiales
Sus antecedentes:
- Los polímeros cíclicos ofrecen propiedades únicas, pero su comportamiento mecanoquímico se entiende menos que las contrapartes lineales.
- Las unidades de gem-diclorociclopropano (gDCC) sirven como mecanóforos efectivos, permitiendo la escisión de la cadena de polímero bajo estrés mecánico.
Objetivo del estudio:
- Investigar y comparar el comportamiento mecanoquímico de los polímeros cíclicos que contienen mecanóforos gDCC con sus análogos lineales.
- Determinación de la eficiencia de la activación de los mecanóforos (Φ) durante la fragmentación de la cadena en polímeros cíclicos.
Principales métodos:
- Síntesis de polímeros cíclicos con mecanismos múltiples de gDCC a través de la polimerización por metástasis de expansión de anillo.
- Investigación de la mecanoquímica de los polímeros mediante ultrasonidos pulsados.
- Análisis de productos mecanoquímicos mediante ozonólisis para evaluar las zonas de activación.
Principales resultados:
- Los polímeros cíclicos mostraron una fracción más baja de mecanóforos gDCC activados por evento de mediación de la cadena (Φ = 0,38) en comparación con los análogos lineales (Φ = 0,62).
- La ozonólisis reveló una zona de activación mecanoquímica menos continua en los polímeros cíclicos frente a los lineales.
- La fragmentación de los polímeros cíclicos se produce a través de intermedios lineales que se someten a una escisión adicional dentro del mismo evento.
Conclusiones:
- La activación reducida de los mecanóforos en polímeros cíclicos sugiere que el intermedio lineal formado durante la fragmentación retiene una memoria de su conformación cíclica.
- Este "efecto de memoria" influye en los sucesos de escisión posteriores, lo que lleva a un patrón de activación menos continuo en comparación con los polímeros inicialmente lineales.
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