Boosting or moderating surface-initiated Cu(0)-mediated controlled radical polymerization with external additives

Surface-initiated Cu(0)-mediated controlled radical polymerization (SI-CuCRP) has been proved to be a powerful method for the fabrication of polymer brushes with various architectures. A key factor in the SI-CuCRP process is the copper disproportionation/comproportionation equilibrium, yet little is known about how the equilibrium works in controlling polymer brush growth, especially under external additives. In this work, the regulation of such equilibrium in SI-CuCRP via external additives is reported in more detail. We find that the polymer brush growth rate can be enhanced via decreasing the ligand concentration or adding NaBr, while it can be reduced by adding ascorbic acid. In addition, the concentration of CuBr2 regulates the ratio of [CuI]/[CuII] to tune the polymer growth kinetics and grafting density over a wide range, which is independent of the distance between the copper plate and initiator-modified substrate. Besides, ultrafast polymerization (surface-initiated hydrogel formation) can be achieved when the ratio of [CuBr2] : [ligand] reaches 1 : 2. This work gives a deeper insight into the SI-CuCRP process and facilitates the fabrication of polymer brushes on demand.