All polymer syntheses were carried out via ATRP. The homopolymerization of styrene, methyl methacrylate, and benzyl methacrylate was initiated by PDI-diBr or PDI-tetraBr to generate linear or 4-arm polymers, respectively. Different degrees of polymerization (DPs) were achieved by varying the monomer/initiator feeding ratio. In a typical procedure, 1.0 equivalent (eq.) of the initiator was loaded in a dry Schlenk flask, along with CuBr (1.5 eq.) and 4,4′-dinoyl-2,2′-dipyridyl (dNbpy, 1.5 eq.). The Schlenk flask was evacuated and refilled with argon through several cycles to remove oxygen. In the meantime, the monomer was deoxygenated by bubbling argon for at least 20 min. Desired amounts of the degassed monomer were added to the Schlenk flask using a syringe under argon. The Schlenk flask was heated at 80°C in an oil bath overnight. It was then removed from the oil bath and cooled down with water to stop the reaction. Last, the brown residue was consecutively dissolved in THF, filtered through a basic alumina column, precipitated once in hexane and twice in methanol, and then dried under vacuum overnight. The final product was obtained and ready for further analysis. The polymers were characterized by 1 H NMR spectroscopy (Figure ), gel permeation chromatography (GPC) (Figure ), and powder X-ray diffraction (Figure ). For details see also Measurements section in Supporting Information.