Melt Fluidity And Thermal Property Of Thermosetting Siloxane-Containing Polyimide Resins And Their Organic/Inorganic Hybrid Characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)(2)SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 degrees C revealed relatively higher glass transition temperatures (T-g) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D [(CH3)(2)SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 degrees C, D[(CH3)(2)SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the T-g even exceeding 550 degrees C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 degrees C.