Design and synthesis of heteroatoms-doped porous carbon model materials with controllable nitrogen contents and similar pore structure are of great importance for fundamental understanding of the correlation between their intrinsic properties and applications. Herein, we report a synthetic strategy for synthesis of nitrogen-doped hollow carbon nanospheres with variable nitrogen contents, similar pore structure and morphology by pyrolysis of mixed polymer brushes formed through surface-initiated atom transfer radical polymerization of monomer mixtures of styrene and 4-vinylpyridine. With increasing 4-vinylpyridine fractions in the monomer mixture, nitrogen contents in the final carbon products increase up to about 5.5 wt%. As example applications, electrocatalytic performance for oxygen reduction reactions in both basic and acidic media and carbon dioxide adsorption properties of the thus-formed materials are investigated to evaluate the synthetic approach. The results reveal that the higher nitrogen contents doped in carbon do not guarantee the better performance for either electrocatalysis or carbon dioxide adsorption. It is the fraction of pyridinic nitrogen that dominates the electrocatalytic activity and carbon dioxide adsorption capacity. The findings demonstrate that mixed polymer brushes are promising precursors for the formation of heteroatoms-doped carbon materials, particularly as model materials for fundamental understanding their structure-properties correlations.