High energy consumption is a crucial challenge in gas separation processes. With current energy intensive separation methods, there is a real need for more energy-efficient alternative technologies. Membrane technology demonstrates potential uses in industrial separation processes due to its potential energy efficiency, environmental friendliness, and small footprint. The continuous developments in material science contributed directly in enhancing the membrane performance through several engineering modifications such as thermal annealing, which presented visible improvements in gas permeation properties. The objective of this project was to investigate the thermal annealing of three fluorinated polymers (PAE1, PAE2, and TFMPD), aiming for favorable changes in gas permeation properties. In particular, each polymer was annealed for 3 h at various temperature values, targeting the intermediate stage, which is the zone where degradation started but a pure carbon structure stage was not formed yet. Overall, the thermal annealing study revealed that TFMPD had highest pure-gas separation performance among other polymers, in which the Robeson plots displayed that treated sample at 500 ºC surpassed the 2015 H2/CH4 upper bound, whereas the treated sample at 550 ºC surpassed 2019 upper bound of both CO2/CH4 and CO2/N2. Therefore, TFMPD can be a potential candidate polymer for membrane-based gas separation, especially for CO2 and H2 applications. This performance could be attributed to the internal structural changes in the polymer that occurred during thermal annealing. Hence, several characterization techniques were performed to detect these changes. For instance, it was realized that all polymers started crosslinking upon the thermal treatment at 350 ºC. Moreover, FTIR analysis indicated the release of several functional groups from treated polymers at high temperature values. Raman spectroscopy also confirmed that the observed substantial enhancement in gas permeation of annealed TFMPD at 550 ºC was due an early-stage carbon structure formation. Furthermore, several recommendations are proposed to continue the work in this project, which could lead to potential success of the thermally annealed polymers tested in this study in membrane-based gas separations applications.