Thermal rearrangement of hydroxyl-containing polyimides in solid state formed microporous polybenzoxazoles showing extraordinarily fast molecular transport for small gas molecules. Their microporous structure and size distribution can be tuned easily by varying the chemical structure of the precursor hydroxyl polyimide and by using different thermal treatment protocols. This manuscript reports, for the first time, the synthesis of ether containing polybenzoxazole, that is, poly(ether-benzoxazole) (PEBO) membranes by thermal rearrangement of a novel fluorinated poly(o-hydroxy ether-imide). The effect of increased chain flexibility on the physical and transport properties of the resultant thermally rearranged (TR) polymer membranes for different thermal treatment protocols (e.g., final temperature and thermal dwell time) have been examined and reported in detail.