Morphology, microstructure, and rheology of amphiphilic telechelics incorporating polyhedral oligosilsesquioxane

Amphiphilic telechelics incorporating polyhedral oligosilsesquioxane (POSS) end-caps were synthesized and studied as a novel building block for the construction of inorganic-organic hybrid materials. Their micron-scale morphologies were investigated using hot-stage polarizing optical microscopy (POM), revealing a dramatic influence of POSS macromer incorporation. The molecular-scale crystalline microstructures of amphiphilic POSS telechelics were investigated using wide-angle X-ray diffraction (WAXD), revealing significant crystallinity for both POSS-rich and PEO-rich microdomains. This observation clearly indicates that distinct microstructures form from the covalently linked POSS endcaps and PEO bridges. Covalent endcapping by POSS macromers also disrupts the crystallization of PEO for particular compositions, resulting in less ordered PEO crystallites. Further evidence for microphase separation is given by rheological experiments on a selected amphiphilic POSS10k telechelic (Tel10k) that shows evidence for an order-disorder transition (ODT) akin to block-copolymer behavior. We conclude that POSS moieties, attached to both ends of PEG, aggregate and crystallize as nanocrystals.