using the nano-foam approach. However, fluorinated polymers have inadequate thermal stability for use in integration procedures, and there are issues for fluoric acid evolution during processing and reactions with the metals used [182, 183] . Block copolymers usually consist of a highly temperature-stable block and a thermally labile block that acts as the dispersed phase through the curing process, which makes them good candidates for templates. Thermolysis of the labile blocks leaves pores of sizes and shapes that correspond to those present in the initial copolymer's morphology. A number of reports [179, 180, 182] described the synthesis of porous structures of high temperature thermoplastic materials (Tg > 350°C) from block copolymers. Lee et al. [184] synthesized nano-porous polyimide films through the use of a hybrid poly(ethylene oxide)-polyhedral oligosilsesquioxane (PEO-POSS) template. Reduced dielectric constant of k = 3.25-2.25 of the porous hybrid films with pore sizes in the range of 10-40 nm were reported. Table 6.4 [184] gives the dielectric constants of the various composites having different POSS contents.

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