Effects of monomer rigidity on the microstructures and properties of polyimide aerogels cross-linked with low cost aminosilane

Abstract

Polyimide aerogels were formed from polyamide acid oligomers cross-linked by Si–O–Si network structures, which were derived from hydrolysis and condensation reactions of low cost bis(trimethoxysilylpropyl) amine (BTMSPA). To investigate the effects of the chemical structures on their properties and microstructures, polyimide aerogels produced using hybrid diamines with different rigidity are evaluated. It is found that polyimide aerogels with rigid building blocks (PI-RBs) have a density in the range of 0.245 to 0.300 g cm⁻³ depending on the uncontrollable shrinkage (27–36%), and high Young's modulus of 50–76 MPa. While polyimide aerogels with flexible building blocks (PI-FBs) exhibit lower shrinkage of 8–15%, lower density ranging from 0.124 to 0.172 g cm⁻³, and a lower modulus of 28–34 MPa. Their various performances are closely related to the nanostructure difference between the particulate PI-FBs and the fibrous PI-RBs. The diverse morphology has been attributed to the different rigidities of their repeat units. Over all, the obtained polyimide aerogels are all excellent high-temperature thermal insulation materials with low thermal conductivity of 0.033–0.049 W (mK)⁻¹ at room temperature and 5% weight loss temperature at about 550 °C in N₂.