The design and synthesis of novel copolymers consisting of a linear block of methoxypoly(ethylene glycol) (mPEG) and a dendrimeric poly(ether-sulfide) block with potential applications in drug and gene delivery are described. The copolymers bear hydroxyl or alkene functional groups at the periphery and were prepared via a divergent approach using mPEG, allyl chloride, and 3-mercapto-1,2-propanediol as starting materials. Copolymer (G3.5) with alkene chain ends was functionalized with cysteamine and its number average size in aqueous medium was determined by dynamic light scattering. The compounds prepared in this work were characterized by NMR spectroscopy and MALDI-TOF. The ability of the copolymers to solvate pyrene and form micelles was investigated by UV and fluorescence spectroscopies. The ability of G3.5-amino copolymer to condense nucleic acids was studied by gel shift. Circular dichroism was used to investigate the effect of the polymer on nucleic acid conformation. Polymer cytotoxicity was determined by MTT assay.