Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP)

Abstract

Polyimide aerogel monoliths are prepared by ring-opening metathesis polymerization (ROMP) of a norbornene end-capped diimide, bis-NAD, obtained as the condensation product of nadic anhydride with 4,4 0 -methylenedianiline. The density of the material was varied in the range of 0.13À0.66 g cm À3 by varying the concentration of bis-NAD in the sol. Wet gels experience significant shrinkage, relative to their molds (28%À39% in linear dimensions), but the final aerogels retain high porosities (50%À90% v/v), high surface areas (210À632 m 2 g À1 , of which up to 25% is traced to micropores), and pore size distributions in the mesoporous range (20À33 nm). The skeletal framework consists of primary particles 16À17 nm in diameter, assembling to form secondary aggregates (by SANS and SEM) 60À85 nm in diameter. At lower densities (e.g., 0.26 g cm À3 ), secondary particles are mass fractals (D m = 2.34 ( 0.03) turning to closed-packed surface fractal objects (D S = 3.0) as the bulk density increases (g0.34 g cm À3 ), suggesting a change in the network-forming mechanism from diffusion-limited aggregation of primary particles to a space-filling bond percolation model. The new materials combine facile one-step synthesis with heat resistance up to 200 °C, high mechanical compressive strength and specific energy absorption (168 MPa and 50 J g À1 , respectively, at 0.39 g cm À3 and 88% ultimate strain), low speed of sound (351 m s À1 at 0.39 g cm À3 ) and styrofoam-like thermal conductivity (0.031 W m À1 K À1 at 0.34 g cm À3 and 25 °C); hence, they are reasonable multifunctional candidate materials for further exploration as thermal/acoustic insulation at elevated temperatures.

Preparation and Characterization of Highly Cross-Linked Polyimide Aerogels Based on Polyimide Containing Trimethoxysilane Side Groups

“…In comparison with some previous reports about polyimide aerogels, the polyimide aerogels showed relatively high shrinkage. 25,30,32 In addition, the shrinkage of the polyimide aerogel increased with increasing the concentration of polyimide containing trimethoxysiloxane side groups in DMF. Shrinkage was reflected upon the bulk densities of the final polyimide aerogels.…”

“…32 This kind of polyimide aerogel combined facile one-step synthesis with high mechanical strength and specific energy absorption. However, they had unsaturated backbone, which limited their use in air at high temperature.…”

Synthesis and biomedical applications of aerogels: Possibilities and challenges

“…44 crosslinking process is time-consuming and costly, making the purely organic aerogels more appealing [157]. On the other hand, some industrial applications of aerogels [158] demanded highly flexibility and foldability, which cannot be attainable by the polymer-cross-linked silica aerogels.…”

Development of aerogel-lined targets for inertial confinement fusion experiments

“…Toluene (anhydrous, 99.8%, Aldrich) was purged with nitrogen gas prior to use. Poly(dicyclopentadiene-random-norbornene) (P(DCPD-r-NB) gels were prepared from ring opening metathesis polymerization (ROMP) [46,[53][54][55][56] of DCPD and NB in toluene with Grubbs' 1 st generation catalyst [57]. Density of the P(DCPD-r-NB) aerogels and gelation time were adjusted by the DCPD/NB-to-toluene and the DCPD/NB-to-catalyst ratio, respectively.…”