Preparation, microstructure, and property characterizations of fluorinated polyimide–organosilicate hybrids

Synthesis of organosilicate (orgSiO2) via sol-gel process utilizing tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) as precursors was carried out in this work. Various amounts of orgSiO2 were blended with fluorinated poly(amic acid) (PAA) to form the PAA–orgSiO2 precursors and the fluorinated polyimide (PI)–orgSiO2 (i.e., the HR1) thin-film hybrids were prepared via spin coating and curing treatments. The PI–orgSiO2–AP (i.e., the HR2) hybrids were also prepared by using the PAA–orgSiO2 precursors containing the amine silane coupling agent, the 3-aminopropyltriethoxysilane (APTEOS). The effects of APTEOS on promoting the crosslinking between organic and inorganic components as well as the network formation were investigated. Fourier-transform infrared spectroscopy (FTIR) showed that the orgSiO2 particles indeed formed in the hybrids due to the emergence of absorption bands corresponding to SiOSi and OSiO bonds. Nuclear magnetic resonance (NMR) analyses revealed that the Q4 units or, the four bridging bond units, dominate the structure of orgSiO2. Thermal analysis indicated that the implantation of orgSiO2 in PI matrix may effectively improve the thermal stability of hybrids. Transmission electron microscopy (TEM) revealed the formation of nano-scale orgSiO2 particles in both hybrids and the sizes of orgSiO2 are relating to the Si content. In HR1 hybrids, the particles obviously coarsened when Si content was high while, in HR2 hybrids, the addition of APTEOS effectively suppressed the phase separation and the ultrafine orgSiO2 particles as small as 5 nm could be achieved in the sample with high Si content. Dielectric measurements showed that the lowest values of dielectric constants are 2.40 and 2.20 for HR1 hybrid at intermediate Si content = 0.4 mol and HR2 hybrid with the highest Si content = 0.8 mol, respectively. The suppression of dielectric constants was attributed to the absence of polar SiOH and SiH2O functional groups as well as the completion of hydrolysis in the hybrids. Formation of silica xerogels in the hybrids should be another cause of dielectric constant decrement, as indicated by the porosity calculation. Experimental results implied that the control of orgSiO2 size to imply the closed-form silica structure is essential to the low-dielectric constant properties of hybrids. Leakage current density measurement illustrated that no deterioration effect occurs due to the addition of orgSiO2 nanoparticles in polymeric matrix and satisfactory electrical properties are preserved for the hybrids for advanced low-dielectric applications.