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.

A series of multistage (pressure-sensitive/hot melt) adhesives utilizing dynamic thia-Michael bonding motifs are reported. The benzalcyanoacetate Michael acceptors used in this work undergo bond exchange under ambient conditions without external catalysis, facilitating pressure-sensitive adhesion. A key feature of this system is the dynamic reaction-induced phase separation that lends reinforcement to the otherwise weakly bonded materials, enabling weak, repeatable pressure-sensitive adhesion under ambient conditions and strong adhesion when processed as a hot melt adhesive. By using different pairs of benzalcyanoacetate cross-linking units, the phase separation characteristics of the adhesives can be directly manipulated, allowing for a tailored adhesive response.

Although the catalyst-free dynamic thia-Michael (tM) reaction has been leveraged for a range of significant applications in materials science and pharmaceutical development, exploiting its full potential has been limited by relatively low equilibrium constants. To address this shortcoming, a new series of catalyst-free, room-temperature dynamic thia-Michael acceptors bearing an isoxazolone motif were developed and utilized to access both dynamic covalent networks and linear polymers. By leveraging the generation of aromaticity upon thiol addition and tuning the electronic-withdrawing/donating nature of the acceptor at two different sites, a wide range of equilibrium constants (K eq ∼1000 to ∼100,000 M–1) were obtained, constituting a 2 orders of magnitude increase compared to their noncyclic benzalcyanoacetate analogues. Integration into a ditopic isoxazolone-based Michael acceptor allowed access to both bulk dynamic networks and linear polymers; these materials not only exhibited tailorable thermomechanical properties based on thia-Michael acceptor composition, but the higher K eq tM bonds resulted in more mechanically robust materials relative to past designs. Furthermore, solution-state formation of linear polymers was achieved thanks to the increased K eq of the isoxazolone-based acceptors.