A Novel Bio‐Based Unsaturated Copolyester With Tunable Structure and Properties: Synthesis, Characterization, and Performance of PPeSAB and Its Nano‐Silica Composites

ABSTRACT Unsaturated polyesters (UPs) are widely used thermosetting polymers due to their excellent mechanical strength, chemical resistance, and processability. In this study, a novel bio‐based unsaturated copolyester, poly(1,5‐pentanediol‐co‐3,4‐butanediol succinate‐co‐adipate) (PPeSAB), was synthesized from bio‐derived 3,4‐butanediol, 1,5‐pentanediol, succinic acid, and adipic acid via a two‐step melt polycondensation. The synthesis was optimized to minimize side reactions, yielding high‐molecular‐weight copolyesters ( M n = 7.7 × 10 4 g/mol) with well‐controlled composition. By adjusting the monomer feed ratios, the material properties could be tuned from rigid plastic to soft elastomer, and the copolyesters exhibited excellent low‐temperature performance ( T g < −61°C). Incorporation of nano‐SiO 2 further improved mechanical strength, achieving tensile values comparable to linear low‐density polyethylene. The fully aliphatic ester backbone also suggests potential environmental advantages, associated with its highlighting the material's promise for sustainable polymer applications. These findings provide a rational strategy for designing bio‐based unsaturated polyesters with tunable thermal and mechanical properties.