Irreversible Low Critical Solution Temperature Behaviors of Thermal-responsive OEGylated Poly(l-cysteine) Containing Disulfide Bonds

High Resolution Image Download MS PowerPoint Slide Three cysteine derivatives were synthesized in high yield by ligating monomethoxy oligo(ethylene glycol) (OEG) to l -cysteine thiol group using sulfenyl chlorides. These OEG groups containing di-, tri-, and tetra-EG units were linked with l -cysteine via disulfide bond. The three monomers were then converted into corresponding N -carboxyanhydrides (NCAs) using triphosgene in THF. Subsequent ring-opening polymerization (ROP) of disulfide bond containing NCAs gave three poly-EG x - l -cysteine derivatives. The obtained poly-EG x - l -cysteine with x = 3 and 4 displayed thermal-responsive behaviors in water, but the temperature-induced phase transition was found surprisingly irreversible. Such irreversible thermal-responsive behaviors were attributed to cross-linking arising from disulfide bonds exchanges. Using PEG-NH 2 as macroinitiator, we also prepared two PEG- b -poly-EG x - l -cysteine diblocks, which could undergo irreversible thermal-induced sol–gel transition, which was caused by the disulfide bonds exchanging reactions. These hydrogels displayed partially shear-thinning and rapid recovery properties allowing new capabilities to construct stimuli-responsive injectable hydrogels in biomedical applications.