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

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 gamma-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 degrees C indicating their potential toward sustained release of drug-loaded hydrogels.