In the first part of this work, we verified the nonfouling properties and pH sensitivity of mixed-amine copolymers. Secondary amines are potentially proton sponging, tertiary amines are proton sponging and positively charged under slightly acidic conditions for DNA condensation, and quaternary amines are positively charged under all pH conditions to ensure DNA condensation. We measured the nonspecific protein adsorption, DNA binding and release, and the pH responsiveness of CBMA-ester polymer brushes containing mixtures of secondary/tertiary and tertiary/quaternary amine groups. In the second part of this work, the biophysical properties of CBMA-ester polymers containing different ratios of secondary/tertiary amines and tertiary/quaternary amines were studied, as were the corresponding nanoparticles. Specifically, we examined how changing the amine content of the polymers affects the polymer's ability to condense DNA into a nanoparticle, the resulting nanoparticle size and surface charge, the pH responsiveness of the bulk polymer and its corresponding nanoparticle, and the buffering ability of the nanoparticles. Finally, we have successfully transfected cells with the luciferase plasmid, and here we compared the transfection efficiencies of mixed-amine CBMA-ester polymers. We have correlated the transfection efficiencies with the biophysical characteristics and chemical properties of the polymers. Here we identify tertiary/secondary and tertiary/quaternary amine ratios that most effectively balance endosomal escape and nanoparticle packaging to induce COS-7 cells to express luciferase.