New polyimide nanocomposites based on silicate type nanotubes: Dispersion, processing and properties

Novel magnesium hydrosilicate [Mg3Si2O5(OH)(4)] nanotubes (SNTs) were synthesized and used as fillers for polyimide nanocomposites. New polymer nanocomposites containing SNTs and polyimide matrices such as PMDA-ODA (denoted by PIPAA-PM) and Ultem((R))-1000 were prepared with SNT concentrations <= 12 vol% (or similar to 20 wt%) to yield new materials with improvements in stiffness, strength and barrier properties. It was found that the SNT particles can be readily dispersed homogeneously in the polyimide matrices by using a special solvent mixing/casting method (PIPAA-PM films) and melt-blending method (Ultem((R))-1000 thermoplastic nanocomposites) at elevated temperatures that are well below the thermal degradation temperature of the SNT particles. The PIPAA-PM/SNT and ULTEM (R)-1000/SNT nanocomposites exhibited significant improvements in mechanical properties with increasing SNT concentrations, as well as adequate strain to failure (or ductility). Dielectric and gas barrier measurements of the polyimide nanocomposites revealed a reduction in the dielectric constant and improvements in the gas barrier properties as a function of the SNT concentration. The gas barrier behavior was found to be consistent with the Nielsen's equation and the expansion approximation equation reported by Fredrickson and Shaqfeh. Because of their facile synthesis and desirable properties for a number of applications in protective coatings and films for microelectronic applications and flammability reduction, these polyimide nanocomposites are expected to be excellent model systems for exploring mechanisms of reduction in dielectric constant of polyimides filled with hollow nanoscale inorganic tubes, a very important and desirable characteristic in microelectronic applications. (c) 2007 Elsevier Ltd. All rights reserved.