Wang Yuepeng,Yang Lei,Zhang Luzhi,Huang Hongfei,Qian Bo,Gu Shijia,You Zhengwei
Polyurethane is widely used for its versatility in design and range of performance. Self-healing and recyclable dynamic polyurethane networks have attracted extensive attention due to their potential to extend service life and ensure safety in use, as well as to promote sustainable use of resources. Developing green and environment-friendly methods to obtain this material is an interesting and challenging task, as the majority of current dynamic polyurethane networks utilize the solution polymerization method. The use of solvents makes the processes complicated, harmful to environment, and increase the cost. Poly(oxime-urethanes) (POUs) are emerging dynamic polyurethanes and show great potential in diverse fields, such as biomaterials, hot melt adhesives, and flexible electronics. In this study, we utilized the solubility properties of dimethylglyoxime in raw material poly(ethylene glycol) to prepare POUs through bulk polymerization for the first time. This method is simple, convenient and cost-efficient. Simultaneously, copper ion coordination improves POUs strength and dynamic properties, with mechanical strength up from 0.54 MPa to 1.03 MPa and self-healing recovery rate up from 85.5% to 91.8%, and activation energy down from 119.6 kJ/mol to 95.4 kJ/mol. To demonstrate the application of this technology, self-healing and stretchable circuits are constructed from this dynamic polyurethane network.
Comparing to the solvent-based and waterborne polyurethanes (PU), the solvent-free reactive PU (RPU) is prepared via in-situ polymerization and film-formation of isocyanate-capped prepolymers and macromolecular polyols in solvent-free system. Thus, the carbon emissions and environmental pollutions are significantly reduced. However, the rapid polymerization also challenges the well control of structure and properties, especially the ordered microstructures. In this work, an efficient approach is applied to enhance the mechanical property of RPU via chemically bonding cellulose nanocrystals (CNCs) with isocyanates in a solvent-free system. The well distributed spot-like structure in the RPU film is realized and significantly improve the mechanical property due to the synergistic effect of hydrogen bonds and urethane bonds. Only adding 1 wt% of CNCs, the tensile strength and elongation at break are profoundly increased to 25.4 ± 1.5 MPa and 748 ± 50.0%, respectively. Both values are 490% and 16% better than that without CNCs. Additionally, the thermal stability is also improved. The initial decomposition temperature is 29 °C higher than that without CNCs. This approach provides a simple method for developing bio-based RPU with well-ordered structures, showing great potential in applications such as environmentally friendly materials and high-performance polymers.
Fang Zizheng,Shi Yunpeng,Mu Hongfeng,Lu Runzhi,Wu Jingjun,Xie Tao
Delicate geometries and suitable mechanical properties are essential for device applications of polymer materials. 3D printing offers unprecedented versatility, but the geometries and mechanical properties are typically fixed after printing. Here, we report a 3D photo-printable dynamic covalent network that can undergo two independently controllable bond exchange reactions, allowing reprogramming the geometry and mechanical properties after printing. Specifically, the network is designed to contain hindered urea bonds and pendant hydroxyl groups. The homolytic exchange between hindered urea bonds allows reconfiguring the printed shape without affecting the network topology and mechanical properties. Under different conditions, the hindered urea bonds are transformed into urethane bonds via exchange reactions with hydroxyl groups, which permits tailoring of the mechanical properties. The freedom to reprogram the shape and properties in an on-demand fashion offers the opportunity to produce multiple 3D printed products from one single printing step.
危险品化学品经营许可证（带存储）