A propanediol monoester cross-linkable (PDMC) polyimide was synthesized for high-speed hollow fiber membrane spinning. The membranes were plasticization resistant and asymmetric, useful for natural gas purification. In fabricating the membrane material, it was found that significant chain scissioning could occur during the monoesterification reaction, which caused problems in subsequent membrane formation processes. Using NMR, GPC, and FTIR, it was observed that hydrolytic degradation occurs at the imide rings from the small amount of water produced during monoesterification. Workable synthesis conditions were found that enabled the cross-linkable polyimide to be synthesized with high conversions and without loss in the polymer molecular weight. The preservation of a high molecular weight (M-w > 100 000) was shown to be favorable for hollow fiber membrane formation.