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Natural gas purification via membrane separation is a promising method that could potentially result in a considerably cost-effective and sustainable purification process. A number of polymers have been studied; however, the two polymers that stand out are polyimide and polybenzoxazole. Among the two polymers, polybenzoxazole has better separation properties mainly because of the size and distribution of its free volume elements. Polybenzoxazole is made through the thermal rearrangement of a polyimide which is formed via the condensation reaction of diamine and dianhydride precursors. Everything from its permeation properties to the path of its formation have been studied. However, a glaring paucity within these studies exists: there are no studies that directly compare the dianhydride precursors of the polyimides and their effects on the resulting polybenzoxazole. The aim of this research is to compare the permeability and selectivity properties of thermally rearranged polybenzoxazole membranes formed by the condensation reaction of a diamine and four different dianhydride precursors. The four precursors are presented below. Out of the four dianhydride precursors to be examined, the BPDA is expected to have the optimum separation properties due to its bridging group.