Molecular Design and Synthesis of Chalcogen-Containing Benzoxazines: Unraveling the Effect of Chalcogen Atoms on the Polymerization Mechanism and Thermal Properties of Polybenzoxazines

Abstract

To develop highly thermally stable thermoset materials and achieve a deep understanding of the chemical structure–physical property relationship of polybenzoxazines, a series of chalcogen-containing bis-benzoxazine monomers (PH-O, PH-S, PH-Se, and PH-Te) were designed and synthesized in the current work. The chemical structures of chalcogen-containing bis-benzoxazines were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance, and high-resolution mass spectrometry. In addition, their polymerization behaviors were systematically investigated using differential scanning calorimetry, in situ FT-IR spectroscopy, and computational calculations. The results revealed that benzoxazines incorporating heavy chalcogen atoms with lower electronegativity exhibit a pronounced tendency toward ring-opening polymerization at lower temperatures. Moreover, the thermal degradation and flame retardant characteristics of the resulting chalcogen-containing polybenzoxazine thermosets were evaluated using thermogravimetric analysis and microscale combustion calorimetry, respectively. Notably, the chalcogen-containing polybenzoxazines displayed significantly reduced flammability compared to those polybenzoxazines without chalcogen atoms. These findings provide valuable insights into the effect of chalcogen atoms on the polymerization mechanism and thermal properties of polybenzoxazines, presenting a promising strategy for the development of thermosets with low curing temperature as well as enhanced thermal stability and flame retardancy.