Effective Modulation of Reactivity, Processability and Thermal Properties of Melamine-Based Benzoxazine Resins by the Introduction of Benzeneguanoamine

Melamine-based benzoxazine resins overcome the disadvantages of conventional polybenzoxazine, such as high brittleness and difficult processing. However, the reactivity is too high to be easily processed. In this work, phenolphthalein-type melamine-based benzoxazine (PTma-BG) was synthesized from paraformaldehyde, phenolphthalein, melamine, and benzeneguanoamine. The chemical structure of PTma-BGs was characterized by fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance ( 1 H NMR), and the curing behavior and properties of the resulting polymers were verified. The results demonstrate that the incorporation of benzeneguanoamine facilitates the formation of the oxazine ring while simultaneously reducing the reactivity of the PTma-BGs precursor, prolonging the gelation time, and expanding the processing window. Poly(PTma-40BG) has good thermal stability; it has been observed that the T d5 of Poly(PTma-40ma) reaches 328°C, which is higher than that of Poly(PTma). Furthermore, Poly(PTma-BG)s demonstrate exceptional heat resistance, with a glass transition temperature exceeding 285°C. The introduction of benzeneguanoamine results in a reduction in the number of polar groups, which in turn leads to a decrease in both water absorption and dielectric constant.