Investigation on the Effects of Bridging Groups in Aromatic Diphenol-Based Benzoxazines: Curing Reaction and H Bonds

A bridging group is an indispensable element for the preparation of diphenol-based benzoxazines, and inevitably, its electronic features will affect the H-bond formation of obtained benzoxazine, which is a crucial factor that not only makes a difference on curing behaviors of benzoxazine but also poses significant influence on the performances of cured resins. However, systematical investigation about the effects of the bridging group on the H bonds in benzoxazine is still in a barren state. Herein, we bridge the gap with three high-purity model benzoxazine monomers. The results showed that electron-donating bridge groups made the benzoxazine monomers tend to start the curing reaction earlier, whereas the electron-withdrawing bridging groups had the opposite effect. In addition, it was also confirmed that the H bonds in polybenzoxazine could be readily tailored by carefully selecting the bridge groups of aromatic diphenols. In this work, some basic characteristics about benzoxazine have been revealed, which are helpful for us to understand its structure–properties relationship more deeply.