This paper shows that tailorable polymeric scaffolds on a molecular scale could be achieved through the ring opening reaction of a three-membered N-heterocyclic compound, aziridine. Aziridine is incorporated into an elastomeric polymer backbone (here, PDMS) through Pt(0)-catalyzed hydrosilylation, retaining attractive features such as optical transparency and elastic properties compared to conventional PDMS. The resulting aziridine-containing PDMS is chemoselectively and regio-specifically post-modified through an orthogonal ring opening reaction of the aziridine and takes advantage of the wide substrate scope of aziridine chemistry.