Preparation and Evaluation of Poly(Ester‐Urethane) Containing Diels–Alder Adduct as Thermoset Adhesive With Self‐Healing Property

ABSTRACT This study develops thermoset adhesives with self‐healing capabilities and improved metal adhesion by incorporating urethane bonds via a non‐isocyanate pathway, simultaneously reducing the use of toxic isocyanates. An unsaturated poly(ester‐urethane) (PEBU) was synthesized using a urethane diol obtained through a non‐isocyanate route. The PEBU was then functionalized with furfuryl alcohol via a Diels–Alder (DA) reaction to incorporate pendant hydroxyl groups, yielding the resin fPEBU. This resin was cured with a polyisocyanate crosslinker (PM200) to produce the final adhesive. The properties of the resulting adhesive were compared to a control resin (fPEB) lacking the non‐isocyanate urethane segments. The crosslinked network obtained from fPEBU polyol and PM200 exhibited excellent self‐healing capabilities upon mild heating due to a retro‐DA reaction and the positive influence of hydrogen bonding interactions. Crucially, the fPEBU‐based adhesive demonstrated a 50% higher adhesion strength (5.1 MPa) than the fPEB‐based control (3.4 MPa), underscoring the role of enhanced hydrogen bonding from the main‐chain urethane groups. Moreover, after failure, these adhesives recovered around 70% of their original strength by thermal treatment. This hybrid strategy significantly reduces overall isocyanate consumption while leveraging non‐isocyanate chemistry to implant superior functionality into the polymer backbone, demonstrating dual environmental and performance merits.