Polymerization mechanism of 1,3-benzoxazine catalyzed by PCl5 and rearrangement of chemical structures

Ring-opening polymerization of benzoxazine monomers is a complex process and various chemical structures including N,O-acetal structures, phenolic Mannich structures and arylamine Mannich structures are formed in polybenzoxazines. To understand the polymerization mechanism, the effects of temperature, time and solvent polarity on the polymerization routes, chemical structures and thermal properties were studied. It was discovered that the N,O-acetal structures and the phenoxy structures can be obtained in a low-polarity solvent like dichloromethane at low temperature (-20 degrees C) with the aid of PCl5, while the arylamine Mannich structures can be readily generated in polar solvent like N,N-Dimethylformamide at high temperature (>80 degrees C) in the presence of PCl5. However, the phenolic Mannich structures can be directly formed at high temperature (>180 degrees C) without any catalysts. Upon prolonging the reaction time or elevating the temperature, the phenoxy structures easily rearranged into the N,O-acetal structures or the arylamine Mannich structures. Further increasing the temperature will cause the arylamine Mannich structures to rearrange into the phenolic Mannich structures and even the phenolic methylene structures. Therefore, both phenoxy structures and N,O-acetal structures showed poor thermal stability; while the arylamine Mannich structures possessed lower initial decomposition temperature but higher char yield compared with the phenolic Mannich structures because of the formation of thermally unstable iminium ions and the anchoring of dangling aniline moieties.

Automated summary

Ring-opening polymerization of benzoxazine monomers is a complex process that results in the formation of various chemical structures such as N,O-acetal structures, phenolic Mannich structures, and arylamine Mannich structures in polybenzoxazines. The polymerization routes, chemical structures, and thermal properties are influenced by factors such as temperature, time, and solvent polarity. Different structures exhibit varying thermal stability, with arylamine Mannich structures possessing lower initial decomposition temperature but higher char yield due to the presence of thermally unstable iminium ions and anchoring of dangling aniline moieties.