**2.7 Oxidation and reduction sensitive polymeric material**

Redox polymeric materials can be separated into reduction reactive systems and oxidation reactive processes depending on the nature of a reductive stimulus. Disulfide and diselenide connections are typically seen in the reduction reactive system, which will be disrupted by considerable growth in the cost of nearby reducing molecules such as GSH. Direct production of disulfide coupling and bridging with a disulphide-containing crosslinking agent are basically two strategies for incorporating disulfide coupling in the process. By live or regulated polymerization, disulfide could be incorporated into the polymer as the oligomer (e.g. Reversible addition-cleavage crosslinking polymerization and atomic transfer radical polymerization) [59]. The thiol-disulfide interchange process, which is commonly utilized to create reduction reactive prodrugs including genetic transporters, is another viable method with gentler circumstances (e.g. at room temperature) than the controlled/living polymerization [60]. To stop the drug leaking, polymeric micelles comprising substances can indeed be crosslinked with covalently crosslinking agents (using bis (2,2′-hydroxyethyl)disulfide, dithiodipropionic acid, and their derived products) and afterward the disulfide conduits split to discharge the substances after the micelles meet the goal [61]. Since the bond-breaking energies of the C-Se (244 kJ mol1) and Se-Se (172 kJ mol1) bond formation are lesser than those from the C-S (272 kJ mol1) and S-S (251 kJ mol1) bond formation, replacing the disulfide interconnection with the diselenide connection is a simple approach to strengthen the responsiveness of the redox-sensitive system. However, diselenide link insertion into a polymeric matrix is more difficult than disulfide link formation, and more research into effective synthetic techniques is needed (**Table 1**) [62].

