Design of Eco-Friendly Self-Healing Polymers Containing Hindered Urea-Based Dynamic Reversible Bonds

This work describes an emulsion polymer with self-healing capability based on a dynamic covalent bonding mechanism. A latex prepolymer (LPtB) containing bulky amine units was synthesized via soap-free emulsion polymerization. Then, a one-pot crosslinkable self-healing emulsion polymer was prepared by adding a blocked isocyanurate and a catalyst into the latex prepolymer, and subsequently, a crosslinked self-healing polymer film (cLPtB) was prepared. Syntheses of self-healing polymers were confirmed by Fourier transform infrared, size exclusion chromatography, proton nuclear magnetic resonance, dynamic light scattering, and transmission electron microscopy analyses. A control latex prepolymer (LPH) was also synthesized without bulky amine functionality, and the self-healing properties of crosslinked LPH (cLPH) were compared to those of cLPtB under the same crosslinking and healing conditions. In addition, the effects of drying and crosslinking conditions at various temperatures on the film formation and crosslinking degree of polymer films were evaluated through atomic force microscopy and gel content analysis. cLPtB demonstrated a T_gDMAof 47 °C and onset dissociation of urea linkages at 120 °C, as confirmed by DMA. The cLPtB films exhibited complete restoration of mechanical properties after cutting and healing at a film formation temperature of 80 °C; they exhibited a self-healing efficiency (σSHE%) of 100%. The cLPtB coating surface also manifested a rapid healing process with 100% wound suturing at 100 °C for 5 min, as recorded by optical microscopy.