ABSTRACT
Polyimide aerogels using 1,12-dodecyldiamine (DADD), 3,3'-dimethylbenzidine (DMBZ), and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and cross linked using 1,3,5-triaminophenoxybenzene (TAB) were synthesized. Substitution of the aromatic diamine, DMBZ, with varying amounts of the aliphatic diamine, DADD, increases the flexibility in the backbone structure of the prepared aerogel. These aerogels are also lightweight, low density, have a low dielectric constant, and high modulus. Their overall properties (density, shrinkage, porosity, dielectric constant, water uptake, and modulus) and potential use as a conformal substrate for lightweight, high-performance antennas are discussed.
ABSTRACT
Polyimide aerogels are mechanically strong porous solids with high surface area, low density, and dielectric constants close to 1, making them ideal materials for use as substrates for lightweight antennas. Increasing the flexibility of the polyimide aerogels extends the usefulness for conformal antennas for use on small aircraft such as unmanned air vehicles or personal air mobility vehicles. To this end, polyimide aerogels made with aromatic amines with 4-10 methylene units as flexible spacers between aromatic rings in the backbone have been fabricated. Substituting 25-75 mol % of fully aromatic 2,2'-dimethylbenzidine with these flexible diamines increases the flexibility of polyimide aerogels, making them bendable at thicknesses up to 2-3 mm. The density, dielectric constants, thermal and moisture stability, and mechanical properties of these aerogels were assessed to understand the effect of the amount and length of the methylene spacers on these properties.
