The efficiency of the ideal CO2/N2 and CO2/CH4 membrane separation was examined in relation to the polymer backbone (i.e., polystyrene (PS), Polydimethylsiloxane (PDMS) and functional cationic substituent (i.e., alkyl, fluoroalkyl, oligo (ethylene glycol), and disiloxane). However, these polymers experience physical degradation, which decreases gas permeability over time, as well as competitive sorption by heavy hydrocarbons, which increases CO2 permeability. A strong CO2 gas solubility selectivity that is unaffected by heavy hydrocarbons in the raw natural gas is the result of the ether/ester oxygen groups' attractive interactions with CO2 but not CH4. By using PS and PDMS, we develop a polymer blend of glassy- rubbery, solubility-selective polymers with a high ratio of ether/ester oxygen to carbon to get around these challenges. More free volume and weaker size-sieving properties result from increased CO2/CH4 selectivity in polymers with higher CO2 permeability. By inhibiting competitive sorption, hydrocarbons (such as CH4 and heavy hydrocarbons) in natural gas might increase CO2 permeability by inhibiting CO2 sorption in glassy polymers. Due to the decrease in non-equilibrium volume with time, which may significantly increase gas permeability, thin films of glassy polymers experience physical aging. By developing glassy-rubbery, solubility-selective polymers for CO2/CH4 separation for raw natural gas, we provide a significantly new approach. The permeability/selectivity trade-off has effectively broken by increasing solubility selectivity since the trade-off requires the absence of any particular interactions between polymers and gases. Most importantly, in the presence of high pressure and heavy hydrocarbons, solubility selectivity may be achieved much well than diffusivity selectivity. These rubbery, solubility-selective polymers exhibit strong separation properties near the upper bound when treating simulated natural gas, in contrast to conventional glassy polymers with a high diffusivity selectivity.