Structure And Performance Of Polyhedral Oligomeric Silsesquioxane-Polyimide Copolymer/octaphenylocta Silsesquioxane Nanocomposites

As high-performance materials, aromatic polyimides(PIs) were widely studied in academic and industrial fields and actually applied to a variety of electric, microelectronic, and optoelectronic devices for their reliable and excellent properties. However, even such superior properties of conventional aromatic PI systems were still unable to satisfy the rapid development of the electronic device technologies. To improve their mechanical and dielectric properties, polyhedral oligomeric silsesquioxanes(POSS) with various functionalities had attracted much more attention of materials scientists. The introduction of POSS into polyimides could not only enhance thermal properties and atomic oxygen resistance, but also improve the dielectric property of PI films. But the wider application of the polymers containing POSS was still hindered by the expensive cost of functionalized POSS and difficulty of preparation.In this paper, a kind of network-structure polyimide(PI) was shown to help octaphenyl polyhedral oligomeric silsesquioxane(Ph-POSS) disperse well without any chemical reactions between the Ph-POSS and PI matrices. The PI matrices were synthesized with a series of double-functional polyamide acids(PAA) with different chain lengths and octa(aminophenyl)silsesquioxane(OAPS) which was both the crosslinker and functionalized POSS. The molar ratio of PAAs and OAPS was made consistent strictly to study the influence of the chain lengths on the dispersion of the Ph-POSS in the PI matrices. The dispersion of Ph-POSS in the PI matrices was studied by scanning electron microscope(SEM) and X-raydiffraction(XRD). The thermal and dielectric properties of the composites were also characterized. Remarkably, with Ph-POSS blended in, the glass transition temperatures(Tg) of the POSS/PI composites were changed obviously. At the same time, the influence of chain flexibility of the PAA was also studied.