Reduced thermal rearrangement temperature via formation of zeolitic imidazolate framework (ZIF)-8-based nanocomposites for hydrogen purification

Thermally rearranged polymers are a class of heterocyclic microporous polymers generated by in situ thermal rearrangement (TR) of ortho-hydroxy polyamides or polyimides at elevated temperatures to produce polybenzoxazole (PBO). Poly(hydroxyamide) (PHA) was selected as a model polymer to generate amide-derived PBO (APBO) owing to its lower TR temperature. A nano-size zeolitic imidazolate framework of ZIF-8 was synthesized and incorporated into the PHA matrix to form PHA-ZIF8 nanocomposites. Due to the presence of ZIF-8 inside the PHA matrix, interchain interactions in the PHA matrix may be inhibited that results in a reduced TR temperature for PHA conversion into APBO. Differential scanning calorimetry (DSC) confirmed that the TR temperature of PHA-ZIF8 nanocomposites decreases as a function of ZIF-8 loading. In addition, the conversion of PHA into APBO and the structural integrity of ZIF-8 before and after TR were visualized by Fourier-transform infra-red (FTIR) spectroscopy and X-ray diffractometer (XRD), respectively. Subsequent measurements of gas transport properties of both PHA-ZIF8 and APBO-ZIF8 nanocomposites revealed that the synergistic amalgamation of TR and formation of nanocomposites can boost hydrogen separation performance, particularly H-2/CH4, of APBO-ZIF8-35% close to the 2008 upper-bound.