1 Supporting Information for Star Synthesis Using Macroinitiators via Electrochemically Mediated Atom Transfer Radical Polymerization Sangwoo Park, † Hong Yul Cho, † Katarzyna Barbara Wegner, †,‡ Joanna Burdynska, † Andrew J. D. Magenau, † Hyun-jong Paik, § Stefan Jurga ‡ and Krzysztof Matyjaszewski †,* † Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA ‡ NanoBioMedical Center, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland § Department of Polymer Science and Engineering, Pusan National University, Busan, Korea 609735 KEYWORDS eATRP, star polymers, arm-first, PEO star, controlled radical polymerization.