Synthesis and characterization of polyimide/oligomeric methylsilsesquioxane hybrid films

In this study, polyimide/silsesquioxane hybrid materials were synthesized from aminoalkoxysilane-capped poly(pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) and oligomeric methylsilsesquioxane (O-MSSQ) precursors. The O-MSSQ moiety was used to obtain wen characterized nano-inorganic cage and network structures in the hybrid materials. The effects of molecular structures and composition on the morphologies and properties of the prepared hybrid materials were studied. The phase separation of the prepared hybrid materials could be controlled by varying the molecular weight of the polyimide moiety, the Si-OH end group content of the O-MSSQ or the coupling agent. Homogeneous and transparent hybrid thin films were obtained from the low molecular weight polyimide moiety with a coupling agent, 3-aminopropyltrimethoxysilane (APrTMS). However, microphase separation occurred if the molecular weight of the polyimide moiety was enhanced or was prepared without a coupling agent, as evidenced by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and electron spectroscopy for chemical analysis (ESCA). The high Si-OH content of the O-MSSQ could enhance the bonding density between the organic and inorganic moiety and thus retard phase separation. The thermal and mechanical properties of the prepared hybrid materials were largely improved compared with the parent polyimide, PMDA-ODA, and were demonstrated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal-stress analysis. The hybrid materials showed adjustable refractive index and dielectric constant by varying the O-MSSQ content. The birefringence of the PMDA-ODA was reduced by incorporating the O-MSSQ moiety. This work revealed that the polyimide/O-MSSQ hybrid materials could have potential applications as optical films or low dielectric constant materials. (C) 2004 Society of Chemical Industry.