Low dielectric property of novel mesoporous silica/polymer composites using smart molecular caps: Theoretical calculation of air space encapsulated inside mesopores

Here we demonstrate the fabrication of novel mesoporous silica/polymer composites using smart molecular caps and investigate the low dielectric property. For the preparation of mesoporous silica/polymer composites, the entrance of the mesopores are firstly modified by polysilsesquioxane (POSS) molecules. The large-sized POSS molecules can act as smart caps to prevent a penetration of the polymers into the inside mesopores (to keep the air space in the mesopores). After that, trimethylsilyl (TMS) agents are grafted onto silanol groups at the inner mesopores to reduce the polarity. Then, organically modified mesoporous silicas are mixed with epoxy polymers by mechanical processing. Here, various types organically modified mesoporous silica with different amount of the modified POSS molecules are utilized to prepare the composites. From the specific gravity data, it is proved that 20 wt% POSS modification is the best for effective blocking the penetration of the polymer into the mesopores. In this composite, lots of air space can remain, showing the excellent low dielectric property. On the other hand, when the POSS modification is less, some polymers penetrate the mesopores at the inner parts of the particles, decreasing the air space. In this paper, we propose new parameter "dead pore ratio" and theoretically discuss how much mesopores maintain as air spaces in the composite, which is an important value for understanding for low-k property of mesoporous silica/polymer composites.