The intracellular delivery of nucleic acids requires a vector system as they cannot diffuse across lipid membranes. Although polymeric transfecting agents have been extensively investigated, none of the proposed gene delivery vehicles fulfill all of the requirements needed for an effective therapy, namely, the ability to bind and compact DNA into polyplexes, stability in the serum environment, endosome-disrupting capacity, efficient intracellular DNA release, and low toxicity. The challenges are mainly attributed to conflicting properties such as stability vs efficient DNA release and toxicity vs efficient endosome-disrupting capacity. Accordingly, investigations aimed at safe and efficient therapies are still essential to achieving gene therapy clinical success. Taking into account the mentioned issues, herein we have evaluated the DNA condensation ability of poly(ethylene oxide)(113)-b-poly[2-(diisopropylamino)ethyl methacrylate](50) (PEO113-b-PDPA(50)), poly(ethylene oxide)(113)-b-poly[2-(diethylamino)ethyl methacrylate](50) (PEO113-b-PDEA(50)), poly[oligo(ethylene glycol)methyl ether methacrylate](70)-b-poly[oligo(ethylene glycol)methyl ether methacrylate(10-)co-2-(diethylamino)ethyl methacrylate(47)-co-2-(diisopropylamino)ethyl methacrylate(47)] (POEGMA(70)-b-P(OEGMA(10)-co-DEA(47)-co-DPA(47)), and poly[oligo(ethylene glycol)methyl ether methacrylate](70)-b-poly{oligo(ethylene glycol)methyl ether methacrylate(10)-co-2-methylacrylic acid 2-[(2-(dimethylamino)ethyl)methylamino]ethyl ester(44)} (POEGMA(70)-b-P(OEGMA(10)-co-DAMA(44)). Block copolymers PEO113-b-PDEA(50) and POEGMA(70)-b-P(OEGMA(10)-co-DEA(47)-co-DPA(47)) were evidenced to properly condense DNA into particles with a desirable size for cellular uptake via endocytic pathways (R-H similar to 65-85 nm). The structure of the polyplexes was characterized in detail by scattering techniques and atomic force microscopy. The isothermal titration calorimetric data revealed that the polymer/DNA binding is endothermic; therefore, the process in entropically driven. The combination of results supports that POEGMA(70)-b-P(OEGMA(10)-co-DEA(47)-co-DPA(47)) condenses DNA more efficiently and with higher thermodynamic outputs than does PEO113-b-PDEA(50). Finally, circular dichroism spectroscopy indicated that the conformation of DNA remained the same after complexation and that the polyplexes are very stable in the serum environment.