The ability to specifically down-regulate gene expression using the RNAi pathway in mammalian cells has tremendous potential as a therapeutic and as a tool in basic science. For example, after abdominopelvic surgery, the accumulation of fibrin between adjacent sides of the wound prevents the regeneration of healthy functional tissue, creating an adhesion between the two sites. Small interfering RNA (siRNA) targeted against key proteins in the blood clotting cascade that prevent the degradation of the accumulating fibrin could lead to a decrease of abdominal adhesions. However, a delivery system capable of efficiently and specifically delivering siRNA to the target cells is currently not available. Cationic polymers are some of the most widely studied and commonly utilized gene delivery vehicles, which can self-assemble with nucleic acids through electrostatic interacionts. Limitations of cationic-based gene delivery systems include toxicity, aggregation, and unpacking of the siRNA. The central hypothesis underlying our approach is that a triblock copolymer based on the self-assembling triblock copolymers of poly(ethylene glycol) (PEG45), poly(propylene sulfide) (PPSx) and CGGRKKRRQRRR (TAT, PEG-PPS-S-S-TAT)) can be tailored to complex siRNA via charge and hydrophilic/hydrophobic interactions; moreover, due to its reductive and pH sensitive character take advantage of chemical differences in the cell organelles and cellular pathways to achieve efficient delivery of siRNA. The polymer PEG45-PPSx-pyridyldithio was synthesized using anionic polymerization of propylene sulfide with AIBN as the radical initiator and dipyridine dithione as the end-capping agent. Triblock polymers with different PPS lengths (PEG45-PPS5-pyridyldithio and PEG45-PPS10-pyridyldithio) were synthesized to study the effect of hydrophobic character of the delivery system on complex formation, complex size and transfection efficiency. H-NMR was used to confirm the degree of polymerization of polypropylene sulfide showing a length of 5.056 and 9.648 for PEG45-PPS5-pyridyldithio and PEG45-PPS10-pyridyldithio respectively. The TAT peptide and a control CK12 peptide were bound to the PEG45-PPSx-pyridyldithio polymers using a disulfide exchange reaction between the free thiol of the N-terminal cysteine of the peptide and the disulfide of pyridyldithio of the triblock polymer. The reaction was complete after 2 hours as determined by monitoring the release of 2-pyridinethione at 343nm. The resulting triblock copolymer was purified using flow phase liquid chromatography (FPLC) with a cationic exchange column and 2mM sodium acetate as the liquid phase. Elution was achieved using 5M of salt and monitored using a UV detector. Gel electrophoresis analysis showed that the triblock polymers were able to complex plasmid DNA at a charge ratio (+/) of 2.52 and 2.3 for PEG45-PPS5-TAT and PEG45-PPS5-CK12 respectively. These studies have focused on the synthesis and characterization of a delivery system for siRNA that self-assembles not only based on charge but also based hydrophilic/hydrophobic interactions.