Consequences of Molecular Architecture on the Supramolecular Assembly of Discrete Block Co-oligomers

Abstract

Supramolecular block copolymers composed of discrete blocks have promising properties for nanotechnology resulting from their ability to combine well-defined morphologies with good bulk material properties. Here, we present the impact of a well-defined siloxane block in either the main-chain or present as pendant grafts on the properties of supramolecular block copolymers that form ordered nanostructures with sub-5 nm domains. For this, two types of supramolecular block copolymers were synthesized based on the ureidopyrimidinone-urethane (UPy-UT) motif. In the first, oligodimethylsiloxanes (<i>o</i>DMS) of discrete length were end-capped with the UPy-UT motif, affording main-chain <b>UPy-UT-Si</b> _{<b><i>n</i></b>} . In the second, the UPy-UT motif was grafted with discrete <i>o</i>DMS affording grafted <b>UPy-UT-</b> <i>g</i> <b>-Si</b> _<b>7</b> . For the two systems, the compositions are similar; only the molecular architecture differs. In both cases, crystallization of the UPy-UT block is in synergy with phase segregation of the <i>o</i>DMS, resulting in the formation of lamellar morphologies. The grafted <b>UPy-UT-</b> <i>g</i> <b>-Si</b> _<b>7</b> can form long-range ordered lamellae, resulting in the formation of micrometer-sized 2D sheets of supramolecular polymers which show brittle properties. In contrast, <b>UPy-UT-Si</b> _{<b><i>n</i></b>} forms a ductile material. As the compositions of both BCOs are similar, the differences in morphology and mechanical properties are a direct consequence of the molecular architecture. These results showcase how molecular design of the building block capable of forming block copolymers translates into controlled nanostructures and material properties as a result of the supramolecular nature of the interactions.