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La isomerización termoreversible cis-cisoidal a cis-transoidal de los polifenilacetilenos dendronizados helicoidales
Virgil Percec1, Jonathan G Rudick, Mihai Peterca
1Roy & Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA. percec@sas.upenn.edu
Journal of the American Chemical Society
|October 27, 2005
Resumen
Los polímeros de polifenilacetileno (PPA) dendronizado forman columnas porosas helicoidales que se transforman en estructuras no porosas al calentarse. Este cambio estructural controlado evita la degradación que se ve en el PPA prístino, destacando su estabilidad.
Área de la Ciencia:
- Química de Polímeros La química de los polímeros es la química de los polímeros.
- Ciencia de los materiales Ciencia de los materiales.
- Química supramolecular de las moléculas.
Sus antecedentes:
- Los polímeros de polifenilacetileno (PPA) son conocidos por su potencial en diversas aplicaciones, pero pueden ser propensos a la degradación.
- La dendronización ofrece una ruta para modificar las propiedades del polímero, incluido el autoensamblaje y la estabilidad.
- El control de la conformación y el autoensamblaje de los polímeros es crucial para el diseño de materiales avanzados.
Objetivo del estudio:
- Para sintetizar polímeros de polifenilacetileno (PPA) de alto contenido cis cubiertos con dendrones autoensambladores anfifílicos.
- Investigar la autoorganización, las transiciones de fase y las propiedades estructurales de estos nuevos PPA dendronizados.
- Evaluar la estabilidad conformacional del cis-PPA dendronizado en comparación con el cis-PPA prístino bajo estrés térmico.
Principales métodos:
- Síntesis de PPA dendronizados a través de la polimerización catalizada por Rh de los macronoméricos.
- Análisis de las transiciones de fase utilizando calorimetría de barrido diferencial (DSC).
- Caracterización estructural utilizando difracción de rayos X de ángulo pequeño y ángulo ancho (SAXS / WAXS) en polvo y fibras orientadas.
Principales resultados:
- Los PPAs cilíndricos sintetizados con alto contenido de cis (81-99%) se autoorganizan en redes columnares hexagonales (Phi(h) ((io), Phi(h)).
- Los polímeros con longitudes específicas de dendrón exhibieron una fase cristalina columnar hexagonal (Phi(h,k)) con transiciones de fase reversibles.
- Las PPA dendronizadas formaron columnas porosas helicoidales en las fases Phi ((h,k) y Phi ((h) ((io), que se transformaron en columnas no helicoidales de diámetro más pequeño en la fase Phi ((h) debido al cambio de conformación de la columna vertebral (cis-cisoidal a cis-transoidal).).
- El cis-PPA dendronizado demostró una estabilidad térmica superior, evitando las vías de degradación observadas en el cis-PPA prístino.
Conclusiones:
- La dendronización de cis-PPA permite el autoensamblaje controlado en estructuras columnares ordenadas con porosidad ajustable.
- Las transiciones de fase reversibles son impulsadas por un cambio conformacional único de la columna vertebral, lo que lleva a reordenamientos estructurales.
- El cis-PPA dendronizado exhibe una mayor estabilidad contra la degradación térmica, lo que abre posibilidades para materiales funcionales robustos.
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