Four series of star-like poly (ethylene oxide) have been prepared by incorporating the cross-linkers with tri-reactive cores, tetra-reactive cores, penta-reactive cores, and hexa-reactive cores, respectively. Chemical characterization was performed by Fourier transform infrared spectroscopy. The thermal properties were evaluated by differential scanning calorimetry. The average chain-to-chain distance in polymers was investigated by wide-angle X-ray diffraction. The effect of incorporating the cross-linkers with various reactive cores and multi-arms on the gas transport properties was reported. The relationship between the gas transport properties and physical properties was also discussed. Some of these polymers exhibit outstanding permeation-separation performance for CO2/N-2, exceeding the CO2/N-2 Robeson upper-bound line.