Parameter Optimization of HDI ‐Mediated Chain Extension for High‐Performance PBAT : A Superior Alternative to Conventional Melt Polycondensation

The production of high‐molecular‐weight poly(butylene adipate‐co‐terephthalate) (PBAT) via conventional melt polycondensation is severely hampered by high melt viscosity, thermal degradation, and energy‐intensive processing. This work systematically investigates the chain extension of PBAT with hexamethylene diisocyanate (HDI) via reactive melt‐mixing to address these limitations. We elucidated the effects of precursor molecular weight, HDI content, and processing temperature on the structural and mechanical properties of the resulting PBAT. Under optimal conditions within the investigated range (PBAT‐2.0h precursor, 1.0 wt% HDI, 190°C), chain‐extended PBAT (PBAT‐2.0h‐HDI) achieves high molecular weight ( M n = 63,304 g/mol), high tensile strength (33.4 ± 2.1 MPa), and super elongation at break (1764.7% ± 112.6%). Crucially, comparative analysis reveals that PBAT‐2.0h‐HDI outperforms PBAT synthesized via prolonged direct polycondensation (PBAT‐4.5h) in both molecular weight and mechanical properties, while greatly reducing the total reaction time and acid value. The mechanism involves the formation of high‐molecular‐weight linear chains and a few long‐chain branching structures. As far as we know, the systematic investigation into how precursor PBAT molecular weight governs the structure and properties of chain‐extended PBAT is first reported in this study. This work establishes comprehensive structure–property correlations for HDI‐mediated PBAT chain extension, delivering low‐energy, short‐cycle technical guidance for the production of high‐performance biodegradable PBAT.