At comparable modification levels, zPEI necessitates more polymer to fully condense DNA compared to acPEI. While DNA is fully condensed by bPEI at a polymer:DNA weight ratio of 0.5, zPEI (2-10%) and acPEI (10-20%) require weight ratios of 0.5-1.0 to fully condense. Higher levels of modification in zPEI20 and acPEI (40-50%) maintain a sigmoidal precipitation curve but do not reduce the relative fluorescence to less than 5%, unlike the lower-modified PEIs. Minimal fluorescence in zPEI20 requires polymer:DNA ratios of 3. Higher levels of succinylation (zPEI30 and zPEI40) further reduce polymer:DNA interactions, leading to partial precipitation or even no precipitation of the DNA even at polymer:DNA ratios as high as 6.