Dynamic covalent polymers have received extensive attention due to their unique self-healable and reprocessable properties. Researchers have introduced many types of dynamic covalent bonds into polymers, but the regulation of the same type of dynamic covalent bonds has not been adequately studied. We designed a new type of dynamic covalent bond, the phenol-carbamate bond in polyurethane, and systematically studied the molecular design strategy and the structure-property relationship of the dynamic covalent polyurethanes. The dissociative mechanism of dynamic covalent network rearrangement was clarified by means of stress relaxation and variable temperature FTIR. The prepared materials exhibited excellent self-healing and reprocessing properties. For molecular design, two methods were applied to regulate the dissociation kinetics and initial dissociation temperature of the phenol-carbamate dynamic network. One was to vary the substituent electron effect of phenolic compounds and the other was to change the chemical structure of diisocyanates. Furthermore, we synthesized high-strength, self-healing, surface-modifiable, and patternable polyurethane elastomers as polymer matrix for printing soft electronic circuit. We used dihydroxybenzophenone as a monomer to prepare the cross-linked polyurethane elastomer with both dynamic covalent bonds and UV-sensitive units. The obtained materials possessed tensile strength up to 20MPa and the elongation at break larger than 1000%. The material can be surface grafted with vinyl monomers to change surface hydrophilicity under short time UV irradiation or self-crosslinked under UV irradiation for 10 min. Application of the multi-functional polyurethane materials as a soft substrate for heat transfer printing of flexile electronics was demonstrated.

Dr. Jun XU is now a tenured associate professor in Department of Chemical Engineering, Tsinghua University. He received his B.Sc. and Ph.D. at Dept of Chemical Engineering, Tsinghua University in 1997 and 2002, respectively. In 2011, he was awarded the Alexander von Humboldt Research Fellowship for Experienced Researchers to carry out the collaboration research in University of Freiburg, Germany. In 2012, he was supported by the Program for New Century Excellent Talents in University. He teaches Polymer Processing and Applications, Polymer Physics Lab and Polymer Processing Lab to the undergraduates. His research interests include polymer crystallization, biodegradable polymers, dynamically crosslinked polyurethanes and polyurea, and the materials for smart devices, etc. He was awarded 2003 Beijing City Awards for Science and Technology Progress (Second Class), 2009 China Petroleum and Chemical Industry Association Award for Science and Technology Progress (Second Class), 2010 China Petroleum and Chemical Industry Association Award for Science and Technology Progress (Second Class), Feng Xingde Polymer Prize (for winning "The Best Paper Nomination from China" published in the journal of Polymer in 2011), 2017 China Petroleum and Chemical Industry Association Award for Science and Technology Progress (Second Class).