Hydrothermal polymerization of porous aromatic polyimide networks and machine learning-assisted computational morphology evolution interpretation

Marianne Lahnsteiner; Michael Caldera; Hipassia M Moura; D Alonso Cerrón-Infantes; Jérôme Roeser; Thomas Konegger; Arne Thomas; Jörg Menche; Miriam M Unterlass

doi:10.1039/d1ta01253c

Hydrothermal polymerization of porous aromatic polyimide networks and machine learning-assisted computational morphology evolution interpretation

J Mater Chem A Mater. 2021 Sep 8;9(35):19754-19769. doi: 10.1039/d1ta01253c. eCollection 2021 Sep 14.

Authors

Marianne Lahnsteiner^{1

2

3}, Michael Caldera^{3

4}, Hipassia M Moura^{1

2

3

5}, D Alonso Cerrón-Infantes^{1

2

3

5}, Jérôme Roeser⁶, Thomas Konegger⁷, Arne Thomas⁶, Jörg Menche^{3

4}, Miriam M Unterlass^{1

2

3

5}

Affiliations

¹ Technische Universität Wien, Institute of Materials Chemistry Getreidemarkt 9/165 1060 Vienna Austria.
² Technische Universität Wien, Institute of Applied Synthetic Chemistry Getreidemarkt 9/163 1060 Vienna Austria.
³ CeMM - Research Center for Molecular Medicine of the Austrian Academy of Sciences Lazarettgasse 14, AKH BT 25.3 1090 Vienna Austria.
⁴ Max F. Perutz Labs, Campus Vienna Biocenter 5 Dr.-Bohr-Gasse 9 1030 Vienna Austria.
⁵ Universität Konstanz, Department of Chemistry, Solid State Chemistry Universitätsstrasse 10 D-78464 Konstanz Germany miriam.unterlass@uni-konstanz.de.
⁶ Technische Universität Berlin, Institute of Chemistry Str. des 17. Juni 115 10623 Berlin Germany.
⁷ Technische Universität Wien, Institute of Chemical Technologies and Analytics Getreidemarkt 9/164 1060 Vienna Austria.

Abstract

We report on the hydrothermal polymerization (HTP) of polyimide (PI) networks using the medium H₂O and the comonomers 1,3,5-tris(4-aminophenyl)benzene (TAPB) and pyromellitic acid (PMA). Full condensation is obtained at minimal reaction times of only 2 h at 200 °C. The PI networks are obtained as monoliths and feature thermal stabilities of >500 °C, and in several cases even up to 595 °C. The monoliths are built up by networks of densely packed, near-monodisperse spherical particles and annealed microfibers, and show three types of porosity: (i) intrinsic inter-segment ultramicroporosity (<0.8 nm) of the PI networks composing the particles (∼3-5 μm), (ii) interstitial voids between the particles (0.1-2 μm), and (iii) monolith cell porosity (∽10-100 μm), as studied via low pressure gas physisorption and Hg intrusion porosimetry analyses. This unique hierarchical porosity generates an outstandingly high specific pore volume of 7250 mm³ g^-1. A large-scale micromorphological study screening the reaction parameters time, temperature, and the absence/presence of the additive acetic acid was performed. Through expert interpretation of hundreds of scanning electron microscopy (SEM) images of the products of these experiments, we devise a hypothesis for morphology formation and evolution: a monomer salt is initially formed and subsequently transformed to overall eight different fiber, pearl chain, and spherical morphologies, composed of PI and, at long reaction times (>48 h), also PI/SiO₂ hybrids that form through reaction with the reaction vessel. Moreover, we have developed a computational image analysis pipeline that deciphers the complex morphologies of these SEM images automatically and also allows for formulating a hypothesis of morphology development in HTP that is in good agreement with the manual morphology analysis. Finally, we upscaled the HTP of PI(TAPB-PMA) and processed the resulting powder into dense cylindrical specimen by green solvent-free warm-pressing, showing that one can follow the full route from the synthesis of these PI networks to a final material without employing harmful solvents.