Aromatic polyimides and copolyimides containing bulky t -butyltriphenylmethane units
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Aromatic polyimides and copolyimides containing bulky t‑butyltriphenylmethane units Rafael A. Castro‑Blanco, et al. [full author details at the end of the article] Received: 26 February 2019 / Revised: 15 October 2019 / Accepted: 23 October 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract Triphenylmethane-based polyimides and copolyimides containing bulky t-butyl group (tBu) were obtained by one-step high temperature polycondensation of 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride with diamines of triphenylmethane (TPM) family. The polymers were obtained in quantitative yields with inherent viscosities of 0.45–0.80 dL/g. They exhibited high thermal stability with 5% weight loss above 500 °C and were cast in films with good mechanical properties capable of testing as gas separation membranes. All polyimides were readily soluble in polar aprotic solvents, and the solubility enhanced with the increase in tBu-group content. The amorphous, free-standing membranes were prepared from these polymers, and their permeabilities and selectivities to several gases were measured and discussed with respect to the structural differences in the polymers. It was shown that the presence of bulky tBu-units made the chain packing less efficient; free volume and d-spacing in the polyimides grew accordingly. As a consequence, the membranes with higher content of tBu-groups demonstrated improved permeabilities, showing 1.5–3.0 times higher permeability coefficients depending on the gas tested. The membranes’ separation performance was improved for C O2/ CH4 gas pair in comparison with that of structurally similar polyimides, while it did not change for O 2/N2 pair. Additionally, the mechanism of formation of triphenylmethane diamines in the reaction between aniline and benzaldehydes was investigated in order to optimize the monomer synthesis and to minimize possible side reactions. It was established that the secondary diamines, so-called aminals, were inevitable side products, particularly important in the condensation between aniline and tBu-benzaldehyde. Keywords Polyimides · Soluble polyimides · Diamine triphenylmethane · Gas permeation
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s0028 9-019-03003-7) contains supplementary material, which is available to authorized users.
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Polymer Bulletin
Introduction Aromatic polyimides (PIs) are considered as high performance materials because of their outstanding thermo-mechanical properties, chemical stability and good dielectric strength [1–3]. These properties make PIs suitable for a wide range of applications in dielectrics, coatings and composite materials capable of resisting harsh environmental conditions. PIs are also known as promising materials for gas separation membranes due to their high intrinsic separation for several gas pares [4, 5] and, therefore, are used or may be used for the nitrogen generation (O2/N2 separation) and for the natural gas purifica
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