Elucidating the Role of Pendent Functional Groups in Lignin‐Derivable Polyurethanes

ABSTRACT Bio‐derivable, non‐isocyanate polyurethanes (NIPUs) offer a potentially safer, more sustainable alternative to isocyanate‐based polyurethanes (PUs), though structure–property comparisons are needed to confirm their high‐performance. Herein, PUs and NIPUs are synthesized from petroleum‐derived bisphenol A (BPA) and lignin‐derivable bisguaiacol A (BGA) to elucidate how pendent methoxy (from BGA) and hydroxyl groups (from NIPU chemistry) govern hydrogen bonding, free‐volume effects, and polymer properties. Fourier‐transform infrared spectroscopy shows increased hydrogen bonding of ─OH/─NH groups in BGA‐based systems (BPA‐PU: 90%, BGA‐PU: 97%, BPA‐NIPU: 75%, BGA‐NIPU: 89%) and more ordered C═O hydrogen bonding (BPA‐NIPU: 3% vs. BGA‐NIPU: 26%). NIPUs exhibit ∼8°C higher glass transition temperatures, suggesting hydrogen‐bond‐mediated chain mobility. Mechanical tests reveal a strength–elongation tradeoff: BPA‐PU achieves the highest modulus (2.7 GPa) and strength (∼59 MPa), while BGA‐NIPU shows the greatest elongation (∼95%) and highest toughness (∼7 MJ m − 3 ). Rheology indicates that methoxy and hydroxyl groups slow relaxation, though only methoxy groups reduce dynamic fragility. Contact angle measurements confirm methoxy groups increase hydrophobicity and lower surface energy (<30 mN m −1 ), enabling potential adhesion to low‐surface‐energy substrates. Overall, strategic lignin‐derivable monomer design and NIPU chemistry yield sustainable thermoplastics with tunable thermomechanical, rheological, and interfacial properties, highlighting their promise as easily‐processable, high‐performance materials.