Preparation of Zwitterionic Sulfobetaine End-Functionalized Poly(ethylene glycol)-b-poly(caprolactone) Diblock Copolymers and Examination of Their Thermogelling Properties

To investigate thermogelling behavior, in this study, we prepared a methoxy poly(ethylene glycol)-b-poly(epsilon-caprolactone) diblock copolymer (MPC) with varying hydrophobic poly(epsilon-caprolactone) (PCL) lengths and an MPC featuring a zwitterionic sulfobetaine (MPC-ZW) at the chain end of the PCL segment. The terminal zwitterionic sulfobetaine was stoichiometrically modified to the terminal MPC diblock copolymer. The introduction of the zwitterionic end group lowered the crystallization enthalpies of the PCL block segments and increased the solubility of the diblock copolymer. The MPC and MPC-ZW copolymers thus obtained formed translucent emulsions at room temperature when prepared as 20 wt %. When the temperature was increased above room temperature, MPC and MPC-ZW exhibited a sol-to-gel phase transition. The phase transition and the gelation time of MPC and MPC-ZW were affected by the length of the hydrophobic segments and the zwitterionic end group. Furthermore, introducing a zwitterionic end group into the PCL segment altered the onset temperature of gelation. Thus, we conclude that zwitterionic end groups introduced into PCL segments of distinct lengths could serve as key determinants in the thermogelling behavior of copolymers. (C) 2014 Wiley Periodicals, Inc.