Temperature-sensitive biodegradable poly(ethylene glycol).

We report here that the incorporation of several disulfide bonds along poly(ethylene glycol) (PEG) gives temperature sensitivity, as well as biodegradability to PEG. To synthesize a PEG with temperature sensitivity in a physiologically important range (20-40 degrees C), PEGs with molecular masses of 400 and 600 Da were randomly coupled by disulfide bonds. As the mol ratio of PEG (400 Da) disulfide to PEG (600 Da) disulfide increased from 40:60 to 60:40, the cloud point of the polymer aqueous solution decreased from 35 degrees C to 27 degrees C. The disulfide bonds between PEGs were degraded in the presence of a thiol-containing biomolecule of glutathione in a thiol-concentration-dependent manner.