Constructing Bi-Continuous Poly(urethane-co-amide) Networks from Hydroxylated Oleic Acid via Dynamic Self-Vulcanization for Super-Toughened Polylactic Acid Blends

To demonstrate the applicability of the “dynamic self-vulcanization of bifunctional monomers” strategy for toughening polylactic acid (PLA), hydroxylated oleic acid (HOA) was synthesized via UV-initiated thiol–ene click chemistry, using oleic acid as the starting material. In the presence of an excess molar quantity of hexamethylene diisocyanate (HDI), the dynamic self-vulcanization of bifunctional monomers was employed to design PLA blends featuring extraordinary impact toughness. During the one-pot melt compounding, in situ formation and self-crosslinking of flexible poly(urethane-co-amide) (HPUA) toughening phase, together with its reactive compatibilization with the PLA matrix, were simultaneously accomplished. The aggregation of the HPUA domains enabled the morphological transformation of the PLA blend from a sea-island structure to a partially or fully bi-continuous one. At HPUA contents of 20 wt% or higher, the blend exhibited a bi-continuous morphology with a crosslinked HPUA network, attaining a notched impact strength exceeding 110 kJ/m2 and an elongation at break above 200%. In particular, when the HPUA content reached 20 wt%, the resulting PLA blend exhibited optimal impact toughness, with a notched IS of 132.1 kJ/m2 (30.7 times that of neat PLA). The primary toughening mechanism was determined to be the internal cavitation of the HPUA domains, which subsequently initiates the yielding of the surrounding PLA matrix. This study proposes an applicable and facile method for fabricating polymer materials that possess excellent impact toughness.