Tuning the Thermomechanical Performances of TPU ‐ POSS Composites Through Controlled Microstructural Evolution

The microstructural characteristics of thermoplastic polyurethane (TPU), which play a crucial role in determining its performance, can be effectively tuned through controlled thermal annealing. Herein, we introduce TPU‐polyhedral oligomeric silsesquioxane (POSS) composites and systematically investigate their microstructural evolution under different annealing temperatures to tailor their thermomechanical properties constructively. Two different TPU‐POSS composites were synthesized, one consisting of non‐functional POSS and the other containing functional POSS, in which the TPU chains are possibly covalently bonded to the POSS surface. Upon annealing, this covalently bonded structure becomes more cohesive, accompanied by the formation of stronger hard segment domains (HSDs). As a result, the tensile strength and the elastic modulus of the TPU‐functional POSS composite (annealed at 140°C) are markedly enhanced by 54% and 28%, respectively, compared to Pristine TPU, and notably, it outperforms the TPU‐non‐functional POSS composite, despite containing only 0.5 wt% POSS. However, in all cases, the formation of HSDs controls the mechanical performance. Moreover, the viscoelastic properties of the TPU‐functional POSS composites exhibit remarkable improvement compared to Pristine TPU, particularly at high temperatures. The storage modulus at 130°C increases by 23%, the melt flow temperature rises by 20°C (TPU‐functional POSS composite after annealing at 160°C), and the creep modulus improves by 140% (TPU‐functional POSS composite annealed and tested at 120°C), confirming the suitability of this material for demanding environments. This study examines the microstructural changes of highly interactive TPU‐POSS composite systems, emphasizing the effective aggregation of HSDs during annealing as a means to design and optimize TPU's performance.