Provided is a poly(amino ester) having a polymer backbone comprising at least one secondary amine linkage and at least one tertiary amine linkage in the polymer backbone. Poly(amino ester)s are prepared via the Michael addition of a bis(acrylate ester)monomer to a diamine monomer, wherein the diamine monomer has one primary amino group and one secondary amino group, and can be end-capped by reaction with a suitable reagent. The inventive poly(amino ester)s may be used as vectors for delivery of a bioactive agent, such as DNA, to a cell.