Synthesis and Structural Effects on Thermal, Mechanical, and Tribological Properties of Different Dianiline-Based Bisbenzoxazines

Achieving target properties of polybenzoxazines generally can be realized based on the flexible molecular design capability of benzoxazine monomers. However, the structural effects on mechanical performance, especially in terms of tribological properties, still remain unclear. In this paper, a series of benzoxazine monomers (PH-bzd, PH-ddm, and PH-eda) with various backbones were synthesized by a three-step method using salicylaldehyde, paraformaldehyde, and three different dianilines as raw materials. The chemical structure of each benzoxazine monomer was characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy (FT-IR), and high-resolution mass spectrometry. Their polymerization behavior was investigated using differential scanning calorimetry and in situ FT-IR spectroscopy. In addition, dynamic thermomechanical analysis (DMA), thermogravimetric analysis (TGA), microscale combustion calorimetry, universal material testing machine (UTM), and Shore D hardness (HD) were used to detect the thermal and mechanical properties of the resulting polybenzoxazines. Moreover, the tribological properties of each polybenzoxazine matrix were further systematically evaluated. With this work, we demonstrate the benzoxazine structural effects on the tribological performance for the first time and provide a theoretical basis for the structural design of polybenzoxazines with outstanding tribological performance.