Polymerization Scheme and Chemical Structure of Aromatic Diamine-Based Polybenzoxazines: New Details

The article discusses the polymerization scheme of benzoxazine monomer based on 4,4′-diaminodiphenylmethane (P-ddm) and the chemical structure of polybenzoxazine based on it poly(P-ddm). The polymerization behavior of benzoxazine P-ddm is studied using differential scanning calorimetry (DSC). Solid-state ¹³C MAS NMR is used to determine the chemical structure of poly(P-ddm). It is revealed that the сhemical structure of poly(P-ddm) predominantly consists not of phenolic Mannich bridges, as expected, but of methylene bridges, which indicates the process of deamination of phenolic Mannich bridges. However, no weight loss associated with the expected release of free amine during this process is detected. This may indicate the incorporation of a diamine moiety into the polymer chain through the formation of imine bonds, the signal of which is detected in the ¹³C MAS NMR and FTIR spectra of the poly(P-ddm), and on the ¹H and ¹³C NMR spectra of model polybenzoxazine based on p-cresol and 4,4′-diaminodiphenylmethane poly(pC-ddm). Based on the data obtained, a hypothesis is put forward about the formation of a network polymer, the structure of which consists mainly of methylene and imine units.