The synthesis of a new series of polymers of intrinsic microporosity (PIM) containing vinyl groups and its performance as gas separation membranes are reported. The incorporation of the vinyl group on the spirobisindane backbone was based on the postmodification of the methylated spirobisindane polymers. Generally, the prepared polymers display good solubility and easy processability to form robust films. Characterization of the new polymers was performed by H-1 and C-13 nuclear magnetic resonance spectroscopy, gel permeation chromatography, infrared spectroscopy, thermal gravimetric analysis, and density measurements. The gas permeability of the CO2, N-2, O-2, and CH4 was measured, and selectivities for the CO2/N-2 and CO2/CH4 gas pairs were calculated for the prepared polymers and compared to the values obtained from PIM-1. The two vinyl groups per repeating units enabled the modified homopolymers to engage in it-orbital overlap and conjugation with the pi-orbitals of the aromatic backbone, thus leading to a reduction in CO2 permeability but surpassing the Robeson's upper bound with CO2/N-2 selectivity. The attractive CO2/N-2 gas separation characteristics of the newly synthesized vinylated PIMs might be useful for postcombustion application in the capture of CO2 from power plant flue gases. The chemical versatility of the vinyl groups has been tested in two successful addition reactions (bromination and thiol-ene click).