Effect of three distinctive crosslinking agents on the dielectric properties of as-prepared polyimide aerogels prepared from super-critical fluid technique

Abstract

In this study, the impact of three distinct cross-linking agents—1,3,5-benzene tricarbonyl trichloride (BTC), tris(4-aminophenyl)amine (TAPA), and 3-aminopropyltrimethoxysilane (APTMS)—on the dielectric and thermal properties of polyimide aerogels was investigated. Poly(amic acid) (PAA) was synthesized by reacting diamine ODA with dianhydride BPDA in NMP, followed by cross-linker introduction in acetic anhydride and pyridine. The analysis reveals that BTC and TAPA, both organic cross-linkers with varying aromatic content, influence the dielectric properties differently. APTMS, an organosilane, introduces inorganic siloxane linkages, enhancing the thermal stability of the aerogels.

Key findings include that BTC-crosslinked aerogels achieved the lowest dielectric constant, 1.215, and dielectric loss, 0.025, making them particularly effective for high-frequency applications. In contrast, TAPA and APTMS-crosslinked aerogels displayed higher dielectric constants and losses. Differential Scanning Calorimetry (DSC) revealed that PI-APTMS exhibited the highest glass transition temperature (T_g), followed closely by PI-TAPA, both significantly higher than the non-crosslinked polyimide aerogel (NAPI), indicating excellent thermal properties. The melting points (T_m) of PI-APTMS and PI-BTC were similar, around 294 °C, attributed to the density of structural stacking. At the same time, PI-TAPA exhibited a lower T_m, likely due to its superior network structure.

Thermogravimetric analysis (TGA) further indicated that PI-TAPA had the highest thermal decomposition temperature (T_5d), with all aerogels remaining stable above 420 °C. These results underscore the potential of BTC-crosslinked polyimide aerogels for applications requiring minimal dielectric loss and low constants. We also highlight the influence of organic versus inorganic cross-linkers on thermal and dielectric performance, advancing the field of high-speed communication materials.