Synthesis of polyimide cross-linked silica aerogels with good acoustic performance

Polyimide cross-linked silica gels with different weight percentages of solid precursors and different volumes of MTMS were prepared by using bis(trimethoxysilylpropyl) amine (BTMSPA) cross-linked polyamide acid, synthesized by 4,4'-oxydianiline (ODA), p-phenylenediamine (PPDA) and biphenyl-3,3',4,4'- tetracarboxylic dianhydride (BPDA), compounding with a silica network which was hydrolysed by MTMS, then supercritically dried to produce a hybrid aerogel. The obtained aerogels exhibit striking properties such as low density (as low as 90 mg cm(-3)), a large surface area (up to 582 m(2) g(-1)), lower shrinkage (up to 20%) and are more easily accessible than those previous reported. Formulations made of 8.7% and 11.72% solid precursors never collapsed under compression. Furthermore, the latter shows the maximum modulus (up to 17 MPa) and a higher sound absorption coefficient (more than 0.8) with a thickness of 3 cm in a specific range of frequencies.