As one of the hydrogel components, the redox-responsive hyperbranched polyglycerol was achieved on a 30 g scale through the cationic polymerization of glycidol using 3,3'dithiodipropanoic acid (DTDPA) as a monomer activator in a solvent-free reaction under mild conditions. (Figure ). DTDPA, with its two carboxylic acids (pKa 3.9), can activate the epoxide ring of glycidol toward cationic polymerization. Since DTDPA has two carboxylic acid groups on each end, the polyglycerol backbone could propagate telechelically, ending up with one molecule of DTDPA in the center of the hyperbranched polyglycerol backbone. The suggested mechanism was an activated-monomer (AM) cationic ring opening polymerization (Scheme S1), starting with proton transfer from the DTDPA's carboxylic acid groups to the epoxide ring, resulting in an activated glycidol. The deprotonated carboxylates of DTDPA could further open the activated epoxide rings, resulting in its incorporation in the polymer backbone. The reaction mechanism of carboxylic acid-containing molecules and glycidol has been fully investigated in our group's previously reported work, in which we copolymerized citric acid and glycidol. We should mention that the hydroxyl group of glycidol could also initiate the ring opening, as hydroxyl groups are more reactive in nucleophilic attack than carboxylate, but due to the high concentration of DTDPA and the high reactivity of protonated glycidol, carboxylate groups can also initiate the polymerization.