Molecular-level fabrication strategies for the POSS cross-linked polybenzoxazines

In order to study the dispersion and compatibility of polysilsesquioxane (POSS) with different functional groups in benzoxazine resin, four different polysilsesquioxane/polybenzoxazine (POSS/PBZ) composites are prepared based on 3-phenyl-3,4-dihydro-2H-benzoxazine (PHa), unreactive Octaphenylsilsesquioxane (OPS), Mercaptopropyl-isobutyl silsesquioxane (SPOSS) containing one reactive sulfhydryl group, Aminopropyl-isobutylsilsesquioxane (NPOSS) containing one reactive amino group and Octa (aminophenyl) silsesquioxane (OAPS) containing eight reactive amino groups, respectively. Scanning electron microscope (SEM), transmission electron microscope (TEM), and transmission electron microscope with probe corrector (AC-TEM) are used to investigate compatibility. The results indicate that OAPS have very good compatibility and interaction with benzoxazine in the molecular level based on the microstructure. Besides, molecular and mesoscopic dynamic simulations (MesoDyn) also confirms OAPS and PHa have the best compatibility based on the micro and mesoscopic aspects. Then their properties of thermal stability and glass transition temperature (T_g) are identified by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. While OAPS is beneficial to increase the initial decomposition temperature (T_5%) of PBZ by 26 °C and the T_g by 16 °C, comparing with pure PHa. However, NPOSS and SPOSS aggregate into micron-sized silicon spheres, and OPS precipitates and deposits on the bottom of the resin, which could weaken the property of their thermal stability.