Introduction: Recently, bioreducible poly(amido ethyleneimine)s (SS-PAEIs) have proven to be efficient non-viral gene delivery agents. These SS-PAEIs are relatively stable in the extracellular environment and provide higher gene transfection with lower cytotoxicity than bPEI25k. In the past, many labs have studied PEI and the effects of Mw and branching on transfection and toxicity, however, these parameters are not well characterized for SS-PAEIs. Previous research has shown poly(TETA/CBA), an SS-PAEI, to be an efficient gene delivery vector for in vitro transfections and in vivo local applications. It is expected that increased branching of poly(TETA/CBA) will provide better pDNA protection. It is also expected that the molecular weight and polydispersity index (PDI) will have to be studied in order to optimize vehicle stability and poly(ethylene glycol) (PEG) conjugation for copolymer design to attain improved performance for systemic administration. Methods: Poly(TETA/CBA) was differentially synthesized and purified to study the effects of branching and Mw on efficacy. Following synthesis, basic characterization was performed including GPC, Maldi-TOF, DLS, serum protection, gene transfection and cell cytotoxicity assays. Once these parameters were better understood, a poly(TETA/CBA)-g-poly(ethylene glycol) copolymer was synthesized and screened to assert its effectiveness in forming stable particles, protection of nucleic acid from degradation and maintenance of buffer capacity. Results: Preliminary screening of poly(TETA/CBA) systems demonstrated significantly higher transfection than bPEI25k. Moreover, increased branching did improve pDNA protection in serum, though did not adversely affect its gene delivery or cytotoxicity profile. As expected, the Mn, Mw and PDI do affect the physiochemical characteristics of polyplex formation in PBS and these parameters had to be optimized for appropriate PEG conjugation and copolymer design. Poly(TETA/CBA) populations with wide PDIs and oligomer polycations showed inadequate particle stability in PBS. The high molecular weight fractions of branched poly(TETA/CBA) populations tended to aggregate easier than more polydispersed ones. Lastly, the poly(TETA/CBA)-g-poly(ethylene glycol) copolymer showed reduced surface charge of stable particles in PBS compared to the corresponding homopolymer backbone.