Preparation and characterization of highly hydrophobic fluorinated polyimide aerogels cross-linked with 2,2′,7,7′-Tetraamino- 9,9′-spirobifluorene

Highly hydrophobic fluorinated polyimide aerogels were successfully prepared using a mild sol-gel method at room temperature from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis(trifluoromethyl)- 4,4′-diaminobiphenyl (TFDB), and cross-linked with 2,2′,7,7′-tetraamino-9,9′-spirobifluorene (TASBF). The obtained polyimide aerogels had low bulky density (0.118–0.161 g/cm 3 ), high specific surface areas (440.6–606.7 m 2 /g), small pore diameter (17.08–44.89 nm) and excellent mechanical property. These polyimide aerogels also exhibited high thermal stability in both nitrogen and air atmosphere, and the 5% weight loss occurred at temperatures above 530 °C. The introduction of 6FDA into polymer structures enhanced the hydrophobicity of the prepared polyimide aerogels. After replacing 50 mol % of BPDA with 6FDA in the oligomer backbone, water contact angles of the aerogels increased from 104.5° to 126.5°, and water absorption decreased from 4.3% to 2.1%. The high hydrophobicity makes these polyimide aerogels good candidates for use as thermal insulators in harsh environments and other applications.