Polyurethanes with open‐ and closed‐cage silsesquioxanes: Effects of organic substituents on materials properties

Abstract The physical properties of silsesquioxane materials are commonly controlled by varying the proportion of silane coupling agents with different substituents. In contrast, with cage silsesquioxanes (polyhedral oligomeric silsesquioxane, POSS) that allow for precise molecular design, the material properties can be controlled by isomers, similar to organic materials. In this study, we synthesized polyurethanes with corner‐opened POSS (CO‐POSS) and completely condensed POSS (CC‐POSS) in the main and side chains, respectively. For the substituents on POSS, we used a combination of phenyl and isobutyl groups and investigated their effects on the physical properties by changing this combination. Notably, the thermal and mechanical properties changed in polymers where the substituents of CO‐POSS (main chain) and CC‐POSS (side chain) were interchanged. This demonstrates that the isomeric structure significantly affects the properties of silsesquioxane‐based materials and provides important design guidelines for these materials.