pH/temperature-sensitive poly(aspartic acid)-g-poly(propylene glycol)

A pH/temperature sensitive polymer of poly(aspartic acid) grafted with poly(propylene glycol) (PA-g-PPG) was prepared. The polymer showed lower critical solution temperature in water depending on the pH as well as ionic strength. As the temperature increased, the concentrated poly(propylene glycol) aqueous solution precipitated, whereas the concentrated aqueous solution of PA-g-PPG underwent sol-to-gel transition at pH 7.4. The dehydration of poly(propylene glycol) and ionic repulsion of aspartic acid drive gel formation at pH 7.4 over 30 ~ 50 °C. The PA-g- PPG is expected to be a useful in situ gel forming depot system for drug delivery and tissue engineering applications.