This article reports the preparation and characterization of CO2 sorbents based on hyperbranched polyglycerol containing trimethylammonium hydroxide groups. The influence of humidity and temperature on the capture/release properties of the sorbents is presented. The presence of humidity showed to be critical for the absorption of carbon dioxide. The full sorption capacity was achieved for a moderate relative humidity of 20-40%. Investigated materials were capable of capturing up to 42 mg of CO2 per gram in the form of bicarbonate moieties. Approximately 20% (up to 8.2 mg/g) of this amount could be then reversibly desorbed and absorbed under various conditions. The typical size of the humidity or temperature swing was estimated to be in the range of 0.9-1.1 mg of CO2 per 1 g per hour. In the case of humidity swing, the absorption and desorption times were on comparable levels. In the case of thermal desorption, a short temperature impulse was only needed to fully regenerate the bed. The presented results show that the release of captured CO2 is also possible under dry conditions, which supports the old bicarbonate/carbonate-exchange mechanism. For humid conditions, both old and recently published new mechanisms may be applied, showing that the nature of this process is more complex than expected and depends on many inter-related factors. The investigated sorbents showed to be stable for several capture/release cycles and are promising materials for CO2 capture.