Influence of diamine rigidity and dianhydride rigidity on the microstructure, thermal and mechanical properties of cross-linked polyimide aerogels

Abstract

Polyimide aerogels (PAs) using different monomers were prepared by cross-linking with a low-cost aminosilane, bis(trimethoxysilylpropyl) amine. The influence of diamine rigidity and dianhydride rigidity on the microstructure, thermal and mechanical properties of PAs were investigated independently. It was found that Young's modulus and yield strength of the PAs increase with the increase of rigidity of diamine or dianhydride. PA prepared with the most rigid dianhydride (pyromellitic dianhydride, PMDA) and diamine (4,4′-oxydianiline, ODA) shows the highest Young's modulus of 45.7 MPa, while that prepared with the most rigid diamine (p-phenylenediamine, PPDA) and dianhydride (biphenyl-3,3′,4,4′-tetracarboxylic dianhydride, BPDA) exhibits the highest yield strength of 2.9 MPa. PAs prepared with more flexible diamines tend to form more disordered microstructure with larger pores and broader pore size distribution. Meanwhile, the thermal conductivity of PAs shows a decreasing tendency with the decrease of diamine rigidity. The lowest thermal conductivity of 0.038 W/(m·K) comes from the sample synthesized using ODA and BPDA. Besides, the initial thermal decomposition temperature depends mainly on the diamine, which illustrates that diamine rigidity has a greater effect on thermal stability than dianhydride rigidity. By contrast, no obvious correlation between the dianhydride rigidity and properties of PAs was observed. The obtained PAs exhibit good application potential for aerospace applications and their properties can be tailored by adjusting the monomer rigidity.