Phosphorus/boron-containing, flame-retardant polyurethane elastomers with great mechanical, shape-memory, and recycling performances

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Based on sustainable development strategy and practical application requirement, it is crucial to develop high-strength, recyclable, and flame-retardant polyurethane (PU) elastomers. Hence, a flame-retardant, reprocessable, high-performance polyurethane elastomer (PU-DP 1–7) with dynamic boronic ester bonds and phosphorus-containing groups was well-designed and prepared. The chemical structure of PU-DP 1–7 was confirmed by Fourier transform infrared spectrometry (FTIR) and X-ray photoelectron spectroscopy (XPS). PU-DP 1–7 shows a transmittance of about 60 % at the wavelength of 900 nm, and phosphorus and boron elements are evenly distributed within its surface, confirming the formation of uniform cross-linking network. The inclusion of phosphorus-and boron-containing groups endows PU-DP 1–7 with a vertical combustion (UL-94) V-0 rating, indicative of desired flame retardancy. In addition, PU-DP 1–7 exhibits a tensile strength of 42.7 MPa and an elongation at break of 616.9 %, with high adhesion strengths towards various substrates due to abundant hydrogen bonds within its network. Furthermore, the dynamic borate ester bonds endow PU-DP 1–7 with superior physical recycling and shape-memory properties. After hot-pressing at 130 °C, the reformed PU-DP 1–7 film shows an 83.6 % recovery efficiency in terms of elongation at break. This work presents an integrated strategy to create flame-retardant, recyclable polyurethane elastomers with great mechanical and shape-memory performances by introducing phosphorus-containing segments and dynamic boronic ester bonds.