A series of styrene copolymers grafted with alkyldiamines have been synthesized using a styrene-co-vinylbenzylchloride copolymer precursor. The chain length n of the aliphatic spacer was varied from 2 to 10 (1,10-diaminodecane), using commercially available aliphatic diamines. Of this group, 1,4-diaminobutane-functional copolymers (n = 4) were found to exhibit maximum CO2-sorption capacity. Further, measurement of the decomposition temperature of the CO2-polymer adducts showed a higher thermal stability for polymers functionalized with 1,4-diaminobutane, which seems to support the hypothesis of a cooperative binding of CO2.