In general, since rubber has a weak interaction between molecular chains, if it is not crosslinked, it will flow and cannot withstand actual use. Covalent crosslinked rubber has high mechanical properties due to the strong bonding force of crosslinking, but it is difficult to be reshaped and recycled because of the difficulty to cleave the crosslink. On the other hand, thermoplastic elastomers use physical interactions between molecular chains (physical crosslinking) to suppress fluidity and express physical properties. Therefore, although it can be reshaped by disconnecting the physical crosslink due to heat, it lacks heat resistance (creep resistance). Heat resistance is very important in industrial materials, but thermoplasticity and heat resistance have a trade-off relationship. As an attempt to break this tradeoff, many studies have been reported to use dynamic bonds such as hydrogen bonds, ionic bonds, and dynamic covalent bonds for crosslinking. However, this trade-off has not been resolved. In recent years, for the purpose of improving heat resistance and creep resistance, attempts have been made to introduce static covalent bonds to dynamic bonding crosslinks, which will be explained in this lecture.