The evolution of physicochemical and gas transport properties of thermally rearranged polyhydroxyamide (PHA)

► We study the temperature-dependent thermal cyclization of polyhydroxyamide. ► Degrees of thermal conversion are the same in the resultant polybenzoxazole films. ► Polymer chain rigidity and membrane FFV increase with cyclization temperature. ► Thermal history and thermal crosslinking have played important roles. ► Gas permeability increase is credited to both solubility and diffusivity increase.