In this work, biodegradable branched polycationic polymers were synthesized by Michael addition polymerization from different amine monomers and the triacrylate monomer trimethylolpropane triacrylate. The polymers varied in the number of amines that dissociate in different pH ranges, which are considered to be beneficial to different parts of the gene delivery process. P-DED, a polymer synthesized from trimethylolpropane triacrylate and dimethylethylenediamine, had the highest number of protonated amines that are available for plasmid DNA (pDNA) complexation at pH 7.4 of all polymers synthesized. P-DED formed a positive polyplex (13.9 +/- 0.5 mV) at a polymer/pDNA weight ratio of 10:1 in contrast with the other polymers synthesized, which formed positive polyplexes only at higher weight ratios. Polyplexes formed with the synthesized polymers at the highest polymer/pDNA weight ratio tested (300:1) resulted in higher transfection with enhanced green fluorescent protein reporter gene (5.3 +/- 1.0 to 30.6 +/- 6.6%) compared with naked pDNA (0.8 +/- 0.4%), as quantified by flow cytometry. Polyplexes formed with P-DED (weight ratio of 300: 1) also showed higher transfection (30.6 +/- 6.6%) as compared with polyplexes formed with branched polyethylenimine (weight ratio of 2:1, 25.5 +/-2.7%). The results from this study demonstrated that polymers with amines that dissociate above pH 7.4, which are available as positively charged groups for pDNA complexation at pH 7.4, can be synthesized to produce stable polyplexes with increased potential and decreased hydrodynamic size that efficiently transfect cells, This work indicated that polymers containing varying amine functionalities with different buffering capabilities call be synthesized by using different amine monomers and used as effective gene delivery vectors.