Thermally Rearranged Polybenzoxazoles Containing Bulky Adamantyl Groups from Ortho-Substituted Precursor Copolyimides

A new nucleophilic monomer (2,2-bis­(3-amino-4-hydroxyphenyl)­adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic <i>ortho</i>-hydroxypolyimides (poly­(<i>o</i>-hydroxyimide)­s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of <i>ortho</i>-acetylcopolyimides, <i>o</i>-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis­(3-amino-4-hydroxyphenyl)­hexafluoropropane (APAF) with 2,2-bis­(3,4-dicarboxy­phenyl)­hexafluoro­propane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these <i>o</i>-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the TR process was evaluated by directly synthesizing PBOs, which were made from the reaction, and ulterior thermal cyclization, of 2,2-bis­(4-chlorocarbonylphenyl)-hexafluoro­propane with ADHAB/APAF. TR-PBO membranes made through a thermal treatment at 450 °C for 30 min showed excellent gas separation properties for the CO₂/CH₄ gas pair with values close to the 2008 Robeson limit

Microporous Polymer Networks for Carbon Capture Applications

A new generation of porous polymer networks has been obtained in quantitative yield by reacting two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones having electron-withdrawing groups (trifluoroacetophenone and isatin) in superacidic media. The resulting amorphous networks are microporous materials, with moderate Brunauer–Emmett–Teller surface areas (from 580 to 790 m² g^–1), and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO₂ molecules has been stated. The materials show excellent CO₂ uptakes (up to 207 mg g^–1 at 0 °C/1 bar) and can be regenerated by vacuum, without heating. Under postcombustion conditions, their CO₂/N₂ selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents