Effect of isocyanate structure on bio-based poly(diethylene furanoate)-b- poly(caprolactone) thermoplastic polyurethanes

• PDEF-b-PCL polyurethanes were synthesized with three types of diisocyanates. • The copolymers consisted of crystalline PCL, and amorphous PCL and PDEF phases. • Mechanical properties of PDEF was governed by the stiffness of the isocyanate. • In PCL-based samples crystallinity was promoted by isocyanate segment mobility. • PDEF-b-PCL copolymers had outstanding toughness and increased thermal stability. Thermoplastic polyurethane elastomers combine the durability and toughness of thermoplastics with the elasticity of rubber. Since most conventional polyurethanes are fossil-based, the development of sustainable alternatives is essential. While the composition and phase separation have been explored extensively, only a few reports have systematically examined the effect of isocyanate type on polyurethanes. In this work, bio-based poly(diethylene furanoate)-b-poly(caprolactone) (PDEF-b-PCL) copolymers were synthesized, where diisocyanates with three different structures were used as a chain-extender: methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and dicyclohexylmethane 4,4′-diisocyanate (H12MDI) to systematically evaluate how their structure affects the structure–property relationships of the resulting copolymers. DSC and DMA confirmed that the copolymers exhibited dual-phase transitions, indicating that they consisted of a crystalline phase formed by PCL and an amorphous phase comprising PCL and PDEF. Structural analysis revealed that crystallinity was governed by PCL content and was highest in HDI-based samples, which was the most mobile among the isocyanates. For PDEF, due to its amorphous structure, the tensile properties were mainly influenced by the structure of the isocyanate. The copolymers exhibited enhanced elongation at break compared to the homopolymers, reaching up to 2372 ± 340%, attributed to strain hardening of the PCL crystalline domains and the amorphous PDEF segments acting as physical crosslinks that distributed stress. Some of the copolymers achieved superior toughness up to 233 MJ/m 3 , compared to both PCL and PDEF homopolymers. The incorporation of PDEF significantly improved thermal stability with higher T d,max values, and all copolymers showed higher T d,5% compared to their homopolymer counterparts.