Cationic polymers are provided for delivering anionic active agents, preferably in the form or nanoparticles and other nanostructures. The polymer can be a polycation homopolymer or a copolymer containing a polycation block. The polycations and polycation containing polymers can contain dicarboxylic acid ester units and units of (a-amino acid)-α, ω-alkylene diester units. The nanoparticles can contain high loadings of anionic active agents, with sustained release of the active agents. Methods of making the polycations and polycation containing polymers are provided. Methods of making the nanoparticles and formulating them for administration to an individual in need thereof are also provided.