On July 21, Prof. Christopher Evans (University of Illinois at Urbana-Champaign, USA) was invited to talk about his latest research about regulating the viscoelasticity of polymer networks by dynamic covalent chemistry.

　Dynamic covalent bonds have the characteristics of both covalent and non-covalent bonds, that is, they can break and reform under specific conditions (such as temperature etc.) while having high bond energy. Therefore, they are widely embedded in polymer networks to endow materials with self-recovery and reprocessing properties. However, the introduction of dynamic bonds will greatly affect the relaxation of chain segments, viscoelasticity and the transport of small molecules in the polymer matrix. Prof. Evans systematically described the effect of borate dynamic bonds on viscoelasticity of polymer networks over a wide temperature range (200 K) and revealed the relationship between crosslinking density and molecular scale chemical structure and relaxation patterns of polymer segments. In addition, prof. Evans had discussed the influence of different dynamic bonds on the relaxation behavior of network chains in the same polymer network matrix, and the influence of network structure and dynamic bond exchange on the transport process of small molecules in the polymer network matrix. The teachers and students attending the meeting gained a lot for his systematic and in-depth research on polymer network system with dynamic bonds.

　Prof. Christopher Evans, an assistant Professor at the department of materials science and engineer, UIUC, mainly focused on probing the physics and chemistry of polymer networks, especially on the role of dynamic bond and ion interaction in the network. He received his bachelors in both Chemical Engineering as well as Chemistry from the University of Minnesota and his PhD in Chemical Engineering from Northwestern University. Following a brief stint at UC Berkeley, he moved to UC Santa Barbara to continue his postdoc. He joined the faculty at UIUC in 2016. His professional awards include the Ryan Fellowship, 3M Fellowship, AkzoNobel award, ACS Petroleum Research Fund Doctoral New Investigator award, and a 3M Non-tenured faculty award.