Ultrafast Derived Self-Healable, Reprocessable Polyurethane Elastomer Based on Dynamic “Electrophilic Substitution (ES)-Click” Chemistry

Abstract

Conventional self-healable polyurethanes (PUs) based on the furan–maleimide combination take several hours to prepare and require an elevated temperature to endow self-healing characteristics via Diels–Alder (DA) chemistry. In this work, furan end-capped triarm PU prepolymers (FAPUs) were prepared using polycaprolactone triol, 4,4′-methylene bis(phenyl isocyanate) (MDI), and furfuryl alcohol in the presence of a tin(II) catalyst. Cross-linked FAPUs were accomplished within 10 s under ambient conditions after reaction with bis-1,2,4-triazoline-3,5-dione (bis-TAD) via ES-Click chemistry. Structural elucidation of the synthesized prepolymer and ES-cross-linked FAPUs was carried out by 1H NMR and FTIR analyzes. Differential scanning calorimetric (DSC) analysis revealed that TAD-derived FAPU elastomers were thermoreversible at 110 °C and room temperature via ES-Click chemistry, and the thermoreversibility of FAPUs was confirmed via solution reprocessability. The self-healing behavior of PUs was monitored under an optical microscope, by scanning electron microscopy, and by tensile measurement. Unlike pristine prepolymer with a tensile strength of σ = 0.1 N/mm2, TAD-derived FAPU1 polymer showed a significant tensile strength of σ = 34.68 N/mm2 with healing efficiency (Hσ = 83%) without using any additive. The surface microhardness and depth penetration of FAPUs improved significantly after cross-linking with bis-TAD and retained their properties even after healing. Similarly, the resultant TAD-derived PUs had improved surface hydrophobicity compared to pristine PU prepolymers as supported by AFM analysis. These ES-Click-derived PU polymer materials showed significant mechanical, good self-healing, and hydrophobic characteristics and will be potential materials for advanced coatings, adhesives, and paint applications.