Publication: Síntesis y diseño de nuevos nanorrefuerzos basados en polirrotaxanos y su efecto en una matriz epoxídica
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2014-07
Defense date
2014-07-17
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Abstract
Los polirrotaxanos son estructuras supramoleculares que resultan de la combinación de un
polímero que actúa como esqueleto y numerosas ciclodextrinas, que vienen a ser anillos enhebrados
alrededor de él. Por su elevada relación de aspecto (L/D) y rigidez conformacional, potencialmente
pueden ser utilizados como nanorrefuerzo en una matriz polimérica representando una interesante
alternativa a los nanotubos de carbono, nanofibras y nanovigas de óxidos metálicos. Para estudiar la
validez de los polirrotaxanos como nanorrefuerzo, se ha realizado un estudio sistemático de
nanocomposites en función de la naturaleza y composición del polirrotaxano en una matriz epoxídica. Se
ha elegido un epoxi tipo diglicidiléter de bisfenol A (DGEBA), y se han utilizado diferentes tipos de
polirrotaxanos diseñados y sintetizados en nuestro laboratorio. Variando la naturaleza y el peso molecular
del polímero, así como el número de ciclodextrinas por cadena, se ha conseguido un abanico de
polirrotaxanos con la posibilidad de adoptar distintas conformaciones, capaces de interaccionar con el
medio y auto-asociarse de forma diferente, generando así estructuras únicas.
Se comprobó que el papel de refuerzo del polirrotaxano está limitado por su pobre miscibilidad en
la resina epoxi, lo que dificulta su dispersabilidad en el sistema epoxídico, y por tanto disminuyó la
expectativa de mejora en las propiedades finales. Se optó entonces por dos estrategias (modificación
superficial del polirrotaxano y utilización de métodos de mezclado mecánico), para optimizar las
interacciones y facilitar la dispersión del polirrotaxano consiguiendo una mejora en el estado de
dispersión, sin observar destacadamente una mejora en las propiedades finales. No obstante, se puso en
evidencia que uno de los factores determinantes fue la razón de aspecto de los polirrotaxanos. Así cuando
el polirrotaxano presentó una elevada razón de aspecto (mayor rigidez conformacional), ejercía un doble
efecto en la matriz, ya que mejoró tanto las propiedades mecánicas como la temperatura de transición vítrea (Tg). En cambio, polirrotaxanos con una menor relación de aspecto, presentaban conformaciones
más plegadas sobre sí mismas, provocando un efecto antagónico en la matriz, ya que aunque mejoraban
las propiedades mecánicas de la matriz epoxi, comprometían drásticamente la Tg. ---------------
Polyrotaxanes are supramolecular structures resulting from the combination of a polymer around which numerous cyclodextrins (ring shaped molecules) are threaded. Due to the high aspect ratio (Length / Diameter) and conformational stiffness, they can be potentially used as nanoreinforcements in polymer matrices as an interesting alternative to carbon nanotubes and metal oxide nanowires. Polyrotaxanes with different structures were designed and synthesized in our laboratory and were incorporated in a diglycidyl ether of bisphenol A epoxy matrix (DGEBA). Varying the nature and molecular weight of the polymer as well as the number of cyclodextrins per chain, a wide range of polyrotaxanes were obtained. These supramolecular structures were able to adopt different conformations and to interact with the medium as well as to self-associate generating unique structures. It was proven that the reinforcing effect of the polyrotaxanes was limited by its miscibility with the epoxy resin. Therefore, two strategies were explored in order to optimize interactions and improve the dispersion degree: the surface modification of the polyrotaxane and the use of mechanical blending methods. It was also confirmed that the final properties of the composites are highly dependent on the aspect ratio of the polyrotaxane: high aspect ratio stiff polyrotaxanes improved mechanical properties and increased the glass transition temperature (Tg) of the matrix, while low aspect ratio (high conformational flexibility) although enhancing the mechanical properties, compromised the Tg.
Polyrotaxanes are supramolecular structures resulting from the combination of a polymer around which numerous cyclodextrins (ring shaped molecules) are threaded. Due to the high aspect ratio (Length / Diameter) and conformational stiffness, they can be potentially used as nanoreinforcements in polymer matrices as an interesting alternative to carbon nanotubes and metal oxide nanowires. Polyrotaxanes with different structures were designed and synthesized in our laboratory and were incorporated in a diglycidyl ether of bisphenol A epoxy matrix (DGEBA). Varying the nature and molecular weight of the polymer as well as the number of cyclodextrins per chain, a wide range of polyrotaxanes were obtained. These supramolecular structures were able to adopt different conformations and to interact with the medium as well as to self-associate generating unique structures. It was proven that the reinforcing effect of the polyrotaxanes was limited by its miscibility with the epoxy resin. Therefore, two strategies were explored in order to optimize interactions and improve the dispersion degree: the surface modification of the polyrotaxane and the use of mechanical blending methods. It was also confirmed that the final properties of the composites are highly dependent on the aspect ratio of the polyrotaxane: high aspect ratio stiff polyrotaxanes improved mechanical properties and increased the glass transition temperature (Tg) of the matrix, while low aspect ratio (high conformational flexibility) although enhancing the mechanical properties, compromised the Tg.
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Keywords
Nanocomposites de matriz epoxi, Polirrotaxanos, Nanotecnología