Kinetic Modeling of Ring-Opening Polymerization of Benzoxazines Using MIL-53-Al as a Potent Catalyst

In this study, we report the successful synthesis of a novel Al-based MOF/polybenzoxazine nanocomposite by a facile and green approach via thermally induced ring-opening polymerization (ROP). Structural and thermal characterization of the synthesized nanocomposite was accomplished using FTIR, XRD, BET and TGA, and DSC techniques, respectively. The Al-MOF showed catalytic activity in ROP and good thermal stability compared to the non-catalyzed system. The catalytic impact of MIL-53-Al on the ROP of benzoxazine is revealed by calorimetry at both isothermal and dynamic modes in detail. The Starink isoconversional analysis revealed that the MOF-catalyzed ROP proceeded faster at the reaction’s early stages, typically at α ≤ 40%. The Friedman method was also applied to the experimental data to get more insights into the mechanisms of the ROP reaction. Results indicated that both systems follow a conversion-dependent mechanism for cationic ROP of the benzoxazine. Although the complexity of the ROP of benzoxazines reduces the reliability of model fitting, the activation energy data were confirmed. Moreover, it was demonstrated that the reaction mechanism changes from the autocatalytic to the n-order regime during the reaction. An ROP mechanism is proposed at which the available AlO₄(OH)₂ octahedra act as active sites shifting the curing exotherms to lower temperatures.