Templating amphiphilic poly(ethylene oxide-b-ε-caprolactone) diblock copolymers provides ordered mesoporous silicas with large tunable pores

Abstract

In this study we used evaporation-induced self-assembly (EISA) as a facile approach for the synthesis, with amphiphilic poly(ethylene oxide-b-ε-caprolactone) (PEO-b-PCL) diblock copolymers as templates, of a family of mesoporous silicas with large, tunable pore sizes. Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and N₂ adsorption–desorption isotherms revealed that the morphology transformed and the pore sizes of the mesoporous silica expanded upon increasing the PCL-to-PEO weight ratio in the templating PEO-b-PCL diblock copolymers. We also employed four kinds of homopolymers—two linear poly(ε-caprolactone)s [PCL₂₀ (M_n = 2100) and PCL₄₀₈ (M_n = 42 500)], a star poly(ethylene oxide)-functionalized silsesquioxane [PEO₁₃–POSS (M_n = 5776)], and a linear poly(ethylene oxide) [PEO₂₂ (M_n = 1000)]—as additives during the fabrication of these mesoporous silicas. Pore expansion and a unique mesophase transformation occurred when using PCL₂₀ and PEO–POSS as the additive, respectively. Notably, we obtained highly ordered body-centered cubic (space group Imm) mesoporous silicas with large cage-like pores of 10.1 and 22.6 nm when using EO₁₁₄CL₂₀ and EO₁₁₄CL₂₀/PEO–POSS, respectively, as templates for the EISA process.