Investigation of the chemical and morphological structure of thermally rearranged polymers

• Published in: Polymer (Guilford) 2014-12, Vol.55 (26), p.6649-6657
• Main Authors: Smith, Zachary P., Czenkusch, Katrina, Wi, Sungsool, Gleason, Kristofer L., Hernández, Guiomar, Doherty, Cara M., Konstas, Kristina, Bastow, Timothy J., Álvarez, Cristina, Hill, Anita J., Lozano, Angel E., Paul, Donald R., Freeman, Benny D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Carbon dioxide; Chemical modifications; Chemical reactions and properties; Exact sciences and technology; Gas separation membranes; Nuclear magnetic resonance; Organic polymers; Physicochemistry of polymers; Polybenzoxazoles; Polymers; Precursors; Reactions (nuclear); Solvents; Spectra; TR polymers; Transport properties
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2014.10.055

Reacting ortho-functional poly(hydroxyimide)s via a high-temperature (i.e., 350 °C–450 °C) solid-state reaction produces polymers with exceptional gas separation properties for separations such as CO2/CH4, CO2/N2, and H2/CH4. However, these reactions render these so-called thermally rearranged (TR) polymers insoluble in common solvents, which prevent the use of certain experimental characterization techniques such as solution-state nuclear magnetic resonance (NMR) from identifying their chemical structure. In this work, we seek to identify the chemical structure of TR polymers by synthesizing a partially soluble TR polymer from an ortho-functional poly(hydroxyamide). The chemical structure of this TR polymer was characterized using 1-D and 2-D NMR. By use of cross-polarization magic-angle spinning 13C NMR, the structure of the polyamide-based TR polymer was compared to that of a polyimide-based TR polymer with a nearly identical proposed structure. The NMR spectra suggest that oxazole functionality is formed for both of these TR polymers. Furthermore, gas permeation results are provided for the precursor polymers and their corresponding TR polymer. The differences in transport properties for these polymers result from differences in the isomeric nature of oxazole-aromatic linkages and morphological differences related to free volume and free volume distribution. [Display omitted] •A partially soluble amide-based TR polymer (PA-TR) was characterized by NMR.•NMR results suggest that the PA-TR has a polybenzoxazole (PBO) structure.•An imide-based TR polymer (PI-TR) with similar structure to PA-TR was prepared.•Solid-state NMR suggests the PA-TR and PI-TR have similar PBO structures.•Gas transport in TR polymers is affected by chemical and morphological structure.