Multi-hierarchical responsive polymers: stepwise oxidation of a selenium- and tellurium-containing block copolymer with sensitivity to both chemical and electrochemical stimuli

Nanomaterials with hierarchical responsiveness are of great significance not only for fundamental science but also for future biomedical applications due to sophisticated and hierarchical physiological environments. Herein, we report a selenium- and tellurium-containing block copolymer that can be stepwise oxidized by both chemical methods and electrochemical methods. Differences in sensitivity to the oxidation of selenium and tellurium were employed. By tuning the concentration of the oxidant and oxidation periods, self-assembly behaviors of the copolymer were tuned by stepwise chemical oxidation. After oxidation, some interesting morphological evolution was observed that the polymer micelles crosslinked with each other without any swelling. In the case of electrochemical oxidation, the voltage during the electrochemical oxidation and the oxidation period also affected the level of oxidation. Furthermore, we showed that the degree of electrochemical oxidation varied with a different PEG block length. Considering sophisticated physiological conditions in vivo, this hierarchically responsive system may provide new possibilities as smart delivery vehicles in biological environments.