There are several challenging separation problems in industries which can be solved with the help of membrane technologies. It is the case for instance of the purification of gas energy carriers (i.e. H-2, CH4) from CO2 as well as the CO2 recovery from flue gas. Glassy polymers containing trimethylsilyl residues like poly(1-trimethylsily1-1-propyne) [PTMSP] and polyvinyltrimethylsilane [PVTMS] are known to exhibit good membrane properties for gas separation. This paper reports two ways of improving their performances based on the controlled introduction of selective groups - alkyl imidazomium salts (C4I) and polyethyleneglycol (M-PEG)-able to enhance CO2 selectivity. CO2 Isotherm sorption data and permeability measurements have shown that the membrane performances could be significantly improved when C4I and M-PEG were introduced as residues covalently bounded to the main polymer chain. Moreover the introduced bromine reactive centres could also be used to induce chemical crosslinking giving rise to more resistant and stable membranes to organic vapours. With the C4I groups, the CO2 sorption could be enhanced by a factor 4.4.