Ultra‐Tough <scp>PLLA</scp> Copolymers Synthesized by a Highly Flexible Polyester Macroinitiator Strategy

ABSTRACT Poly(L‐lactic acid) (PLLA), one of the most prosperous bio‐derived synthetic polymers, has garnered significant attention due to its biodegradability and origin from renewable resources. However, its practical applications are limited by its inherent brittleness. In this study, a novel highly flexible polyester macromolecule (FPM) was synthesized via stepwise polycondensation, employing bio‐based diols and diacids. The macromolecular initiator (FPM) was subsequently used to prepare PLLA FPM multiblock copolymers through ring‐opening polymerization (ROP) of L‐lactide, followed by chain extension with hexamethylene diisocyanate (HDI). The chemical structures were investigated by Fourier‐transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance ( 1 H NMR). The differential scanning calorimetry and tensile testing revealed that increasing FPM content reduced crystallinity while dramatically improving ductility—PLLA FPM20 exhibited a 367% elongation at break, ~74 times higher than neat PLLA (5%). These results demonstrate a viable and scalable strategy for producing ultra‐tough PLLA‐based materials via incorporation of bio‐based flexible macroinitiators, offering a tunable balance between mechanical strength and toughness.