A versatile approach to a new family of radially layered copolymeric poly(amidoamine-organosilicon) (PAMAMOS) dendrimers containing hydrophilic polyamidoamine (PAMAM) interiors and hydrophobic organosilicon (OS) exteriors is described. The synthesis involves either Michael addition of organosilicon acrylates or methacrylates to amine-terminated PAMAM dendrimer precursors or their haloalkylation by chloroalkyl- or iodoalkylsilanes. Convenient NMR techniques were developed to monitor the course of these reactions and to enable preparation of products with precisely controlled degree of OS coverage. Compositional variety of the resulting dendrimers is achieved by variation of the generation of PAMAM precursor and the type and functionality of the organosilicon reagent. A range of different PAMAMOS dendrimers was prepared having (a) different number of PAMAM branch cell layers in their interiors, (b) one or two layers of OS branch cells in their exteriors, (c) a variety of inert (e.g., trimethylsilyl or trimethylsiloxy) or reactive (e.g., alkoxysilyl, vinylsilyl, or vinylsiloxy) end groups, and (d) different relative amounts of these end groups. NMR, electrospray-ionization mass spectroscopy, and gel permeation chromatography confirmed the expected structures. Evaluation of selected physical properties of these PAMAMOS dendrimers showed that while solubility and glass transition temperatures were compositionally and architecturally dependent, their thermal and thermooxidative stability were limited by the presence of the less stable PAMAM component.