Preparation and properties of self-healing cross-linked polyurethanes based on blocking and deblocking reaction

Self-healing polyurethane via incorporating reversible bonds obtains great recognition. However, a reasonable design of polyurethane containing reversible bonds with high self-healing efficiency, facile preparing and low costs is still a challenge. Here, we report a novel self-healing polyurethane (Sh-C-PU) containing reversible urethane bonds (-NHCOO-), which was conducted by the reaction of diphenol (tetrabromobisphenol A, TBBPA) and 4, 4'-diphenylmethane diisocyanate (MDI). TBBPA can block the -NCO groups in MDI at 60 degrees C, and -NCO groups can be deblocked at the temperature higher than 90 degrees C, which gave Sh-C-PU self-healing property. FTIR analysis demonstrated thermal reversibility of Sh-C-PU by monitoring the deblocking and reblocking reaction in thermal cycles. In addition, qualitative self-healing phenomenon of cracks was observed under polarizing optical microscopy, and quantitative evaluation of self-healing Sh-C-PU via mechanical properties confirmed the great healing property of Sh-C-PU with healing efficiency by 97.82%, 86.38% and 55.04% for three times self-healing cycles, respectively.