Hydrogen Bond Assisted Assembly of Well-Ordered Polyhedral Oligomeric Silsesquioxane–Block Copolymer Composites

Abstract

Well-ordered block copolymer nanocomposites with d-spacings as small as 15 nm and additive loadings greater than 70 mass % were formed upon blending functionalized polyhedral oligomeric silsesquioxanes (POSS) additives into disordered block copolymers containing poly(ethylene oxide) (PEO) as one of the blocks. The POSS additives were functionalized with maleamic acid or aminophenyl groups as ligands to enable selective hydrogen bonding with the PEO chains. The selective interaction of the additives with the PEO chains caused microphase separation of the block copolymer leading to formation of well-ordered morphologies as evidenced by small-angle X-ray scattering. Further addition of the additive induced transitions between cylindrical and spherical morphologies. While both ligands induced order, the maleamic acid ligand enabled higher levels of incorporation of POSS cages into the PEO phases of the composite. Differential scanning calorimetry and wide-angle X-ray diffraction were performed to confirm compatibility and good mixing of the additives within the PEO phase. The maleamic ligands can be cross-linked by a thermal treatment. The cross-linking was used to stabilize the structure of the composites prior to calcination at high temperatures, which resulted in the formation of mesoporous silica. Transmission electron microscopy showed that the cylindrical and spherical morphologies of the parent composites were maintained in the mesoporous silica.