Triblock copolymers containing UCST polypeptide and poly(propylene glycol): Synthesis, thermoresponsive properties, and modification of PVA hydrogel

Abstract A series of ABA-type triblock copolymers (PImBF 4 -b-PPG-b-PImBF 4 ) comprising of poly(propylene glycol) (PPG) as middle block and UCST polypeptide on both sides of PPG was synthesized by ring-opening polymerization of γ -chloropropyl- L -glutamic acid-based N -carboxyanhydride (CPLG-NCA) and then side-chain modification including nucleophilic substitution of the chloro group followed by copper-mediated 1,3-dipolar cycloaddition and subsequent ion-exchange reaction. Variable-temperature UV–vis spectroscopy revealed that the upper critical solution temperature (UCST)-type cloud point temperature (T cp ) was highly dependent on both polypeptide and PPG chain length as well as polymer concentration. Increasing the polymer chain length or concentration frequently results in T cp increases. Noticeable hysteresis in a cooling/heating cycle was observed for all resulting triblock copolymers owing to a slow disassembly of large aggregates (d = 145 nm) in the heating cycle. Moreover, the resulting UCST triblock copolymers were used to regulate the release property of ciprofloxacin (CIP)-loaded poly(vinyl alcohol) (PVA) hydrogel. The incorporation of PImBF 4 -b-PPG-b-PImBF 4 hampered the burst release of CIP at 37 °C indicating their potential toward sustained release of drug-loaded hydrogels.