Mesoporous silicas templated by symmetrical multiblock copolymers through evaporation-induced self-assembly

Abstract

In this study, we synthesized long-range-ordered mesoporous silicas through evaporation-induced self-assembly (EISA), templated by the ABA-type triblock copolymer PEO-PPO-PEO (F127), and found that the morphologies of the mesostructures could be controlled from a hexagonal cylinder structure to a body-centered cubic (bcc) structure by varying the amount of added tetraethyl orthosilicate (TEOS). In addition, we synthesized the multiblock ABCBA-type copolymer PCL-PEO-PPO-PEO-PCL (PCL-F127-PCL) through ring-opening polymerization (using F127 as the macro-initiator) and then examined the effect of its PCL segments on the morphology of the resulting mesoporous silica. We employed small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N₂ adsorption/desorption isotherms to investigate the mesophase transformations of these mesoporous nanostructures containing various TEOS contents. Upon increasing the molecular weight of the PCL segments, the d-spacing decreased initially, but then increased thereafter. The PCL-F127-PCL multiblock copolymer assembled into an “m”-shaped structure, with the hydrophilic PEO segments folded outside and the hydrophobic PCL and PPO segments aggregated inside. In addition to the relatively strong interactions with the PCL segments, the hydrophilic PPO segments also interacted relatively strongly with the silica matrix, such that some of the PPO segments could enter within it. Using this approach with ABA-type triblock and ABCBA-type multiblock copolymers as templates, we can prepare highly ordered mesoporous silicas having narrow pore size distributions and various mesoporous structures.