Investigation of the chemical and morphological structure of thermally rearranged polymers

Reacting ortho-functional poly(hydroxyimide)s via a high-temperature (i.e., 350 degrees C-450 degrees C) solid-state reaction produces polymers with exceptional gas separation properties for separations such as CO2/CH4, CO2/N-2, and H-2/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 C-13 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. (C) 2014 Elsevier Ltd. All rights reserved.