Synthesis of bio-based poly(diethylene furanoate)-block-polylactide copolymers with UV blocking properties

• Hydroxyl end-capped PDEF was synthesized with different molecular weights. • Bio-based PDEF-b-PLA copolymers were synthesized via ROP and chain extension. • PDEF-b-PLA copolymers have increased thermal stability compared to neat PLA. • PDEF-b-PLA copolymers increased elongation at break while maintaining toughness. • Furan moieties in PDEF and its copolymers provide strong UV blocking below 300 nm. The transition to a circular economy requires the development of bio-based polymers with enhanced functionality to compete with conventional oil-sourced materials. In this study, a bio-based furandicarboxylic acid-containing polyester, poly(diethylene furanoate) (PDEF) was directly copolymerized with polylactide (PLA) for the first time, through the polycondensation of dimethyl furan-2,5-dicarboxylate (MFDC) and diethylene glycol (DEG), used as an initiator for the ring-opening polymerization (ROP) of lactide, followed by chain extension reaction with hexamethylene diisocyanate (HDI) to obtain poly(diethylene furanoate)-block-polylactide (PDEF-b-PLA) alternating multiblock copolymers. The PDEF synthesized with different reaction times exhibited an average glass transition temperature (T g ) of 33.8 °C. The copolymers had PLA segment lengths of 1000 and 300 g/mol after ROP maintaining an amorphous structure with a T g of 34.5 and 33.3 °C respectively, suggesting easy processability. Thermal stability of the copolymers was enhanced, indicated by increased decomposition temperatures and residual weight compared to neat PLA. PDEF displayed elastomer-like behavior while the copolymerization resulted in an intermediate behavior between PDEF and semi-crystalline PLA, with a high Young's modulus of 1.7 and 1.4 GPa, a balanced tensile stress at yield of 24.3 and 28.9 MPa and a significantly increased elongation at break, by 700–1100 % compared to neat PLA. All PDEF-containing samples demonstrated excellent UV-blocking ability due to the furan moiety, effectively blocking UV radiation below 300 nm while maintaining transparency in the visible range. These bio-based PDEF-b-PLA copolymers offer a sustainable alternative for applications such as food packaging and coatings, where thermal stability, mechanical resilience and UV protection are essential.