An aminosilylated substrate was treated with aziridine to prepare hyperbranched polymers on solid supports. It is observed that the primary amine on the substrate is able to initiate the ring-opening polymerization of aziridine. Measuring the thickness of the film and absolute density of the primary amine functionality shows that a very highly branched poly(ethyleneimine) is formed since the primary amine functional group on the very top surface increased dramatically from 3.6 amines/nm(2) to 66-78 amines/nm(2). Atomic force microcopy shows that the polymerization is rather regular laterally and that the morphology of surface has not changed significantly after the polymerization.