Our kinetics and binding affinity results suggest that LPEI and BPEI bind to DNA and form polyplexes through different mechanisms. The kinetics data show that both polymers exhibit a complex, multi-phasic process for binding and packaging DNA. These processes may involve initial electrostatic binding of the polymers to the cargo, followed by structural rearrangements or aggregation further condense the DNA at longer timescales. BPEI complexes, however, show a slight hyperchormism effect after approximately 10 hours, suggesting possible intercalation into the DNA nucleobases that disrupts their π-stacking ? . Additionally, DNA binding to both polymer systems saturate at approximately 80% (Figure , Table ). Both LPEI and BPEI show positive binding cooperativity to DNA with similar affinities. However, BPEI has a higher Hill coefficient (4.4) than LPEI (2.6), indicating stronger cooperativity, likely due to its branched structure, which could enable additional binding modes provided by its primary, secondary, and tertiary amines, compared to LPEI, which only has secondary amines.