Nanostructured Hybrid Binders: Enhancing <scp>HTPB</scp> –Polyurethane Elastomers Through Precise Q‐Siloxane Grafting

ABSTRACT The strategic synthesis of polyhedral oligomeric silsesquioxane (POSS) functionalized hydroxyl‐terminated polybutadiene (gHTPB) and its integration into segmented polyurethane (PU) elastomers is reported. A two‐step platinum‐catalyzed hydrosilylation protocol was developed, utilizing precise equivalents of 1‐octene to partially functionalize octakis(dimethylsiloxy)silsesquioxane (Q 8 M 8 H ) and isolate the mono‐functional intermediate Q 8 M 7 O M 1 H . This intermediate was subsequently grafted onto the vinyl pendants of an HTPB backbone, facilitating the high‐fidelity incorporation of the inorganic POSS cages while maintaining terminal hydroxyl functionality. Subsequent curing with isophorone diisocyanate (IPDI) yielded a series of nanostructured PU hybrid copolymers and terpolymers. This methodology provides a robust route for tailoring the inorganic content and architecture of liquid rubber pre‐polymers, offering a versatile platform for the development of high‐performance elastomeric binders with enhanced thermal and rheological properties.