Compatibility of soluble polyimide/silica hybrids induced by a coupling agent

In this paper, a new type of soluble polyimide/silica (PI/SiO2) hybrid was prepared by the sol-gel process. The coupling agent gamma-glycidyloxypropyltrimethoxysilane (GOTMS) was chosen to enhance the compatibility between the polyimide (PI) and silica (SiO2). Furthermore, the effects of the coupling agent on the morphologies and properties of the PI/SiO2 hybrids were investigated using UV-vis and FTIR spectroscopies and SEM. The densities and solubilities of the PI/SiO2 hybrids were also measured. The results show that the size of the silica particle was markedly reduced by the introduction of the coupling agent, which made the PI/SiO2 hybrid films become transparent. The solubility of the PI/SiO2 hybrid was also improved by the coupling agent. In addition, all of these effects became even more pronounced with increased amounts of the coupling agent. The thermal properties of the compatibilized PI/SiO2 hybrids were investigated by DSC and TGA. Moreover, their mechanical properties were also characterized. The results showed that the glass transition temperatures (T-g) of the hybrids were higher than those of their counterparts without the coupling agent. The thermal stability was lowered by the addition of the coupling agent, but it was still higher than that of the pure polyimide. The compatibility of the two components was effectively improved by the coupling agent; this resulted in the markedly improved mechanical properties.