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 (