Effect of Bulky Substituents in the Polymer Backbone on the Properties of Polyimide Aerogels

Abstract

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.

Reduced Graphene Oxide (rGO)/ZrO2 Reinforced Polyimide Nanocomposite Aerogels with Enhanced Properties: A Synergistic Effect of the Nanofillers

“…The first stage with ϵ<15% (linear region in which elastic deformation occurs and follows Hooke′s law), the second stage with 15%< ϵ< 60% (plateau region) and the third stage with ϵ> 60% (densification region in which the stress increases sharply with the developing of strain and the aerogels change into a dense state) can be seen in Figure (a). Similar phenomenon also appeared in other research work . Since the compression modulus is calculated from the initial linear slope of strain‐stress curve, we can see that whether addition of GO or nano‐sized ZrO 2 separately can all increase compression modulus; when GO and nano‐sized ZrO 2 are incorporated together the compression modulus reverts to nearly that of pure PI instead (also can be seen from Table ).…”

Mechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering Materials

“…In contrast, incorporation of reinforcement additives is a relatively easy technique for improving the mechanical property of cellulose aerogels. The reported wad include graphene [18][19][20][21] , clay [22][23][24] , organic polymers [25][26][27][28] ,…”

Fiber Reinforced Polyimide Aerogel Composites with High Mechanical Strength for High Temperature Insulation

“…The National Aeronautics and Space Administration (NASA) has shown that polyimide aerogels are suitable as materials for preparing extravehicular activity (EVA) suits for planetary surface missions, flexible thermal protection systems (TPS) for entry‐deceleration‐landing (EDL) operations, and a range of other space related applications. PI aerogel networks are comprised of poly‐(amic acid) (PAA) polymers that are synthesized from reaction of dianhydrides with diamines, followed by a thermal imidization process . The resultant aerogels are linear structures formed from physical interactions between polymer chains that can result in poor mechanical properties that are unsuitable for aerospace applications …”

“…PI aerogel networks are comprised of poly-(amic acid) (PAA) polymers that are synthesized from reaction of dianhydrides with diamines, followed by a thermal imidization process. [11][12][13] The resultant aerogels are linear structures formed from physical interactions between polymer chains that can result in poor mechanical properties that are unsuitable for aerospace applications. [14][15][16] Several pioneering studies have attempted to address the brittle nature of these aerogel materials, with multifunctional compounds and nanoparticles being incorporated as cross-linkers into the aerogels to afford 3D network structures that can better withstand applied stresses.…”