The use of pyrolysis mass spectrometry to investigate polymerization and degradation processes of methyl amine-based benzoxazine

In this study, direct pyrolysis mass spectrometry, DP-MS, was applied to investigate curing and polymerization mechanisms of phenol and methyl amine-based benzoxazine monomer, and thermal decomposition and crosslinking characteristics of the corresponding polybenzoxazine. The results indicated opposing polymerization reaction routes besides the generally accepted one. The cleavage of C-O bonds of the oxazine rings either followed by transformation into a polymer constituting ortho or para substituted phenol units or by coupling of -NCH2. Polymerization of the dimer generated by coupling of -NCH2, by either further reactions with benzoxazine monomers or by radicalic vinyl polymerization, yields different polymeric structures. The evolution of alkyl amines and diamines involving more than three carbon atoms at early stages of pyrolysis and the multi-step thermal decomposition detected confirmed this proposal. The formation of char residues were associated with crosslinking of fragments and/or polymer backbone generated by the loss of diamine units and side chains.