Diol Chain‐Length Effects in Adipate and Succinate Polyesters for Thermoplastic Polyurethanes

This work establishes a systematic structure–property mapping of 20 aliphatic polyesters, designed as soft segments for thermoplastic polyurethanes (TPU). Two dicarboxylic acids (adipic vs. succinic acid) and five α,ω‐diols (C2, C3, C4, C5, C6) were combined via melt polycondensation, targeting molar masses of 1000 and 2000 g/mol. Structural fidelity, bi‐functionality, and molar masses were confirmed using FTIR, 1 H NMR, 13 C NMR, end‐group titration, and GPC. Thermal and rheological evaluations revealed a pronounced odd‐even effect: polyesters from even‐numbered diols showed distinct melting transitions, whereas odd‐numbered yielded amorphous materials. For a given diol, succinate‐based polyesters exhibited significantly higher melting points and melt viscosities than their adipate counterparts due to higher ester group density and stronger dipolar interactions. Additionally, the glass transition temperature decreased with increasing methylene content in the diol. These insights provide a practical design tool for tailoring thermoplastic polyurethanes.