Synthesis and characterization of semiaromatic polyimides containing POSS in main chain derived from double-decker-shaped silsesquioxane

A series of semiaromatic polyimides containing polyhedral oligomeric silsesquioxane (POSS) in main chain (POSS-PIs) from a double-decker-shaped silsesquioxane diamine (DDSQ-diamine) (4) with various aromatic tetracarboxylic dianhydrides were prepared and the structures were characterized by IR and NMR spectra. A double-decker-shaped silsesquioxane dianhydride (DDSQDA) (3) was synthesized by hydrosilylation reaction from double-decker-shaped silsesquioxane (DDSQ) (1) and cis-5-norbornene-endo-2,3-dicarboxylic anhydride (2), which then reacted with 4,4'-oxydianiline (ODA) to produce the DDSQ-diamine. The POSS-PIs possessed good thermal stability and mechanical properties, low water absorption, and alkali resistance as well as low dielectric constant. The 5% weight loss temperatures (T-d5) in air were observed at 495-514 degrees C. The polymer films had good mechanical properties with elongation at breakage of 2.9-6.0%, in which POSS-PI 8c derived from 4,4'-oxydiphthalic anhydride (ODPA) exhibits the highest elongation of 6.0%. The water absorption of POSS-PI 8b (< 1%) was much lower than that of PI from pyromellitic dianhydride (PMDA)/ODA (6.0%). POSS-PIs 8 possessed excellent alkaline and acid resistance. POSS-PI 8b kept its flexible mechanical properties when immersed in 5% NaOH solution at 40 degrees C for 72 h. The dielectric constant of POSS-PI 8c measured by precision impedance method was 2.36.