A Hydrazide-PEG Bifunctional Crystallization Promoter Enables Strong, Tough, and Storage-Stable P34HB

Abstract Poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] (P34HB) is a biodegradable polyester with attractive processing potential, but its slow crystallization and storage-induced secondary crystallization compromise its mechanical performance. Here, di(polyethylene glycol)-bis(succinohydrazonoyl) oxalate (BSO-PEG) was designed as a bifunctional crystallization promoter that combines hydrazide-based nucleation with PEG-mediated chain mobility. At 10 wt % BSO-PEG, the crystallization temperature and crystallinity of P34HB increased from 75.5 to 91.5 °C and from 42.6% to 53.7%, respectively. Mechanistic analysis shows that BSO motifs form specific interactions with P34HB and provide nucleation-active sites, whereas PEG segments facilitate chain diffusion and spherulitic growth. Consequently, P34HB/BSO-PEG-10% achieved a tensile strength of 29.9 MPa, a Young’s modulus of 424.1 MPa, and an elongation at break of 27.9%, which are 145%, 196%, and 129% of the neat P34HB, respectively. After 40 d at room temperature, it retained a tensile strength of 30.9 MPa and an elongation at break of 24.3%, indicating the suppression of postcrystallization embrittlement. This bifunctional molecular design offers a practical route to accelerate P34HB crystallization and improve the mechanical stability of biodegradable polyester materials.