NASA Glenn Research Center, 21000 Brookpark Road, Cleveland, Ohio 44135, United States.
ACS Appl Mater Interfaces. 2016 Oct 26;8(42):29073-29079. doi: 10.1021/acsami.6b10248. Epub 2016 Oct 12.
Polyimide aerogels made using anhydride-capped oligomers from 4,4'-oxydianiline (ODA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) cross-linked with 1,3,5-tri(aminophenoxy)benzene (TAB) have been reported with very good mechanical properties but poor resistance to moisture. Replacing 50 mol % of the ODA with poly(propylene glycol)bis(2-aminopropyl ether) (PPG) with an average molecular weight of 230 g/mol in the oligomer backbone gives aerogels with water contact angles of 80°. The aerogels also absorb very little moisture on soaking in water. The aerogels also shrink less with increasing PPG concentration and therefore have significantly lower density and higher porosity than those made without PPG. Mechanical properties of the aerogels increased with increasing density, regardless of the polymer backbone. Brunauer-Emmett-Teller (BET) surface area of the aerogels studied ranged from 300 to 400 m/g, depending mainly on PPG concentration. The high moisture resistance makes them promising materials for substrates for lightweight antennas as well as insulation for a variety of applications.
采用酸酐封端的聚酰亚胺气凝胶，由 4,4'-二氨基二苯醚（ODA）和 3,3',4,4'-联苯四羧酸二酐（BPDA）与 1,3,5-三（氨基苯氧基）苯（TAB）交联而成，具有非常好的机械性能，但耐湿性差。用平均分子量为 230g/mol 的聚丙二醇双（2-氨基丙基醚）（PPG）代替聚酰亚胺气凝胶中 50mol%的 ODA，可得到水接触角为 80°的气凝胶。气凝胶在水中浸泡时也几乎不吸收水分。气凝胶的收缩率随 PPG 浓度的增加而减小，因此其密度比不含 PPG 的气凝胶低，孔隙率更高。气凝胶的机械性能随密度的增加而增加，而与聚合物主链无关。研究的气凝胶的 Brunauer-Emmett-Teller（BET）表面积在 300 到 400m²/g 之间，主要取决于 PPG 的浓度。高耐湿性使它们成为轻质天线基板以及各种应用的绝缘材料的有前途的材料。
