Microstructural Analysis of Benzoxazine Cationic Ring‐Opening Polymerization Pathways

Herein, an evaluation of the initial step of benzoxazine polymerization is presented by mass spectrometry, with a focus on differentiating the phenoxy and phenolic products formed by distinct pathways of the cationic ring opening polymerization (ROP) mechanism of polybenzoxazine formation. The use of infrared multiple photon dissociation (IRMPD) and ion mobility spectrometry (IMS) techniques allows for differentiation of the two pathways and provides valuable insights into the ROP mechanism. The results suggest that type I pathway is favored in the initial stages of the reaction yielding the phenoxy product, while type II product should be observed at later stages when the phenoxy product would interconvert to the most stable type II phenolic product. Overall, the findings presented here provide important information on the initial step of the benzoxazine polymerization, allowing the development of optimal polymerization conditions and represents a way to evaluate other multifunctional polymerization processes. Benzoxazine ring opening polymerization (ROP) mechanism is evaluated by mass spectrometry (MS), including tandem MS, ion mobility spectrometry, and infrared multiple photon dissociation spectroscopy. The ROP iminium intermediate is shown to be present in the polymerization reaction. The first polymerization step is evaluated and showed a preference for the kinetically favored phenoxy product over the thermodynamic phenolic product.