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

Abstract

Synthesis of organosilicate (orgSiO(2)) via sol-gel process utilizing tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) as precursors was carried out in this work. Various amounts of orgSiO(2) were blended with fluorinated poly(amic acid) (PAA) to form the PAA-orgSiO(2) precursors and the fluorinated polyimide (PI)-orgSiO(2) (i.e., the HR1) thin-film hybrids were prepared via spin coating and curing treatments. The PI-orgSiO(2)-AP (i.e., the HR2) hybrids were also prepared by using the PAA-orgSiO(2) 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 orgSiO(2) particles indeed formed in the hybrids due to the emergence of absorption bands corresponding to Si-O-Si and O-Si-O bonds. Nuclear magnetic resonance (NMR) analyses revealed that the Q(4) units or, the four bridging bond units, dominate the structure of orgSiO(2). Thermal analysis indicated that the implantation of orgSiO(2) in PI matrix may effectively improve the thermal stability of hybrids. Transmission electron microscopy (TEM) revealed the formation of nano-scale orgSiO(2) particles in both hybrids and the sizes of orgSiO(2) 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 orgSiO(2) 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 Si-OH and Si-H(2)O 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 orgSiO(2) 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 orgSiO(2) nanoparticles in polymeric matrix and satisfactory electrical properties are preserved for the hybrids for advanced low-dielectric applications. (C) 2008 Elsevier Ltd. All rights reserved.