Sterically hindered amine solutions have been studied extensively for CO2 capture via absorption due to their high theoretical amine efficiencies (1 CO2/N) and weak amine-CO2 species formed. More recently, extensive research has been undertaken on amine-based solids in adsorptive CO2 separations. However, very limited work exists that describes the behavior of sterically hindered amines on solid supports for acid gas separations. To this end, the sterically hindered aminopolymer, poly(2,2-dimethylenimine), is synthesized and incorporated into the pores of mesoporous silica, SBA-15. The CO2 adsorption performance of the hindered polymer/silica composite is compared with unhindered aminopolymer/silica composites under dry and humid conditions using in-situ Fourier-transform infrared spectroscopy and fixed bed breakthrough analysis. The hindered polymer sorbents had lower amine efficiencies when compared with unhindered polymer sorbents under both dry and humid conditions. The addition of poly(ethylene glycol) helps alleviate some of the limitations associated with the hindered aminopolymer/silica composites, improving the CO2 adsorption performance under the conditions studied. The experiments suggest that these hindered polymer sorbents are less effective at CO2 capture than their unhindered polymer counterparts due to the poor molecular mobility and hydrophobicity of the polymer chains.