Polyimide Aerogels with Amide Cross-Links: A Low Cost Alternative for Mechanically Strong Polymer Aerogels

Abstract

Polyimide aerogels combine high porosity, low thermal conductivity, flexibility, and low density with excellent mechanical properties. However, previously used cross-linkers, such as 1,3,5-triaminophenoxybenzene (TAB), 2,4,6-tris(4-aminophenyl)pyridine (TAPP), or octa(aminophenoxy)silsesquioxane (OAPS), either are not commercially available or are prohibitively expensive. Finding more cost efficient cross-linkers that are commercially available to synthesize these aerogels is crucial for making large scale manufacturing attractive. Herein, we describe an approach to making polyimide aerogels starting with amine capped oligomers that are cross-linked with 1,3,5-benzenetricarbonyl trichloride (BTC). BTC is a lower cost, commercially available alternative to TAB, TAPP, or OAPS. Aerogels made in this way have the same or higher modulus and higher surface area compared to those previously reported with either TAB or OAPS cross-links at the same density. While the cross-link structure is an amide, the thermal stability is not compromised most likely because the cross-link is only a small part of the composition of the aerogel. Onset of decomposition depends primarily on the backbone chemistry with 4,4'-oxidianiline (ODA) being more thermally stable than 2,2'-dimethylbenzidine (DMBZ), similar to those previously reported with other cross-links.

Synthesis and characterization of flexible and high-temperature resistant polyimide aerogel with ultra-low dielectric constant

“…The compression stress of the PI aerogel at 10% strain is 0.92 MPa and the Young's modulus is 18.2 MPa. These values are comparable to those mechanically strong PI aerogels reported in ref, [21]. The good mechanical properties for the PI aerogel are mainly attributed to the flexible and tough nature for the PI resin containing rigid biphenyl and benzoxazole moieties.…”

“…However, common organic aerogels usually suffer from their low thermal and dimensional stability at elevated temperatures; thus cannot meet the severe demands of interlayer electrical insulation process for ULSI fabrications. Thus, as a representative high-temperature resistant organic aerogels, PI aerogels have been developed rapidly in recent years [18][19][20][21][22]. The dielectric constants and dissipation factors for PI aerogels have also been investigated in detail.…”

Ultralight and Low Thermal Conductivity Polyimide–Polyhedral Oligomeric Silsesquioxanes Aerogels

“…BTC conveyed similar properties to the aerogel while being available at a lower cost. In any case, the small amount of cross‐linker introduced in the aerogels did not allow a significant improvement of their performance . Cross‐linked polyimide aerogels with optimized properties have not been reported yet.…”

“…The main factors determining the density of an aerogel are the total polymer concentration in the gelation solution and the shrinkage after drying. In previous investigations, the polymer concentration varied from 7 to 12.5 wt%, resulting in the lowest achievable density at 0.077 g cm −3 . Ultralow‐density polyimide aerogels have not been reported and studies on their preparation are still in progress.…”

“…The main shortcoming of linear polyimide aerogels is their high shrinkage. In cross‐linked polyimide aerogels, polyamines and polyisocyanates including 1,3,5‐triaminophenoxybenzene (TAB), 2,4,6‐tris(4‐aminophenyl)pyridine (TAPP), 1,3,5‐tris‐(aminophenyl)benzene (TAPB), 1,3,5‐benzenetricarbonyl trichloride (BTC), and octa(aminophenyl) silsesquioxane (OAPS), have been used as cross‐linkers to react with the anhydrides. The cross‐linked aerogels have comparable density and thermal conductivity to silica aerogels and their compressive modulus ranges between 1 and 5 MPa.…”