The polar functionalization of vinylbenzyl chloride hyper-crosslinked (HCL) resins with ethanolamine at variable functionalization extent is reported. The functionalization reaction was investigated by a multitechnique approach to confirm the reaction mechanism and to calculate the yield of functionalization. Increasing the amount of ethanolamine grafted onto the HCL resin, the total pore volume of the resins decreased, while the microporous fraction increased and the pore size distribution evolved from bimodal to unimodal. The effect of the functionalization on the adsorption properties of the resins was investigated for CO2 sequestration and water purification applications. Both CO2 adsorption capacity and phenol removal efficiency from water solutions over the total pore volume of the resins were significantly improved. Moreover, the CO2/N-2 selectivity significantly increased for the HCL resin at intermediate functionalization degree, which represents the optimal trade-off between high functionalization extent and porosity distribution evolution.