NASA Glenn Research Center , 21000 Brookpark Road, Cleveland, Ohio 44135, United States.
Case Western Reserve University , 2100 Adelbert Road, Cleveland, Ohio 44106, United States.
ACS Appl Mater Interfaces. 2017 Mar 8;9(9):8287-8296. doi: 10.1021/acsami.6b15440. Epub 2017 Feb 23.
With unique advantages over inorganic aerogels including higher strengths and compressive moduli, greater toughness, and the ability to be fabricated as a flexible thin film, polymer aerogels have the potential to supplant inorganic aerogels in numerous applications. Among polymer aerogels, polyimide aerogels possess a high degree of high thermal stability as well as outstanding mechanical properties. However, while the onset of thermal decomposition for these materials is typically very high (greater than 500 °C), the polyimide aerogels undergo dramatic thermally induced shrinkage at temperatures well below their glass transition (T) or decomposition temperature, which limits their use. In this study, we show that shrinkage is reduced when a bulky moiety is incorporated in the polymer backbone. Twenty different formulations of polyimide aerogels were synthesized from 3,3,'4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-oxidianiline (ODA) or a combination of ODA and 9,9'-bis(4-aminophenyl)fluorene (BAPF) and cross-linked with 1,3,5-benzenetricarbonyl trichloride (BTC) in a statistically designed study. The polymer concentration, n-value, and molar concentration of ODA and BAPF were varied to demonstrate the effect of these variables on certain properties. Samples containing BAPF showed a reduction in shrinkage by as much as 50% after aging at elevated temperatures for 500 h compared to those made with ODA alone.
与无机气凝胶相比，聚合物气凝胶具有更高的强度和压缩模量、更大的韧性，并且能够制成柔性薄膜，因此具有取代无机气凝胶在众多应用中的潜力。在聚合物气凝胶中，聚酰亚胺气凝胶具有高度的热稳定性和出色的机械性能。然而，尽管这些材料的热分解起始温度通常非常高（高于 500°C），但聚酰亚胺气凝胶在远低于其玻璃化转变（T g ）或分解温度的温度下会发生剧烈的热诱导收缩，这限制了它们的使用。在这项研究中，我们表明，当在聚合物主链中引入庞大的部分时，收缩会减少。我们从 3,3',4,4'-联苯四羧酸二酐（BPDA）和 4,4'-二氨基二苯醚（ODA）或 ODA 和 9,9'-双（4-氨基苯基）芴（BAPF）的组合合成了二十种不同配方的聚酰亚胺气凝胶，并在统计设计的研究中用 1,3,5-均苯三甲酰氯（BTC）交联。改变聚合物浓度、n 值以及 ODA 和 BAPF 的摩尔浓度，以证明这些变量对某些性质的影响。与仅用 ODA 制成的样品相比，老化 500 小时后，在高温下老化时，含有 BAPF 的样品的收缩率降低了多达 50%。
