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Multilayer hyperbranched polyimide/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by the reaction of a bromidehyperbranched polyether/POSS and a main-chain polyimide containing hydroxyl-functional groups. The first layer was formed through the direct reactions of the main-chain hydroxyl groups with monochloroisobutyl polyhedral oligomeric silsesquioxane (POSS-Cl). The second and third layers were prepared by the repeated reactions of bromine ether branches that incorporated POSS-Cl with 3,5-dihydroxybenzyl alcohol. Regardless of the fixed amount of POSS, the higher layers yielded lower dielectric constants. Even when the amount of the POSS loading was reduced 4-fold, the third layer still had the lowest dielectric constants. The lowest dielectric constant of 2.54 was found in the third layer of the hyperbranched polyimide/POSS nanocomposite because of the large free volume and loose polyimide structures. The densities of the hyperbranched polyimide/POSS nanocomposite corresponded to the dielectric constants. The lower the density was, the higher the free volume was and the lower the dielectric constant was. The experimental results indicated that the hyperbranched polyimide/POSS nanocomposite exhibited increased solubility in comparison with pure polyimide.

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