Novel thermo-responsive double-hydrophilic and hydrophobic MPEO- b -PEtOx- b -PCL triblock terpolymers: Synthesis, characterization and self-assembly studies

A series of new double-hydrophilic and hydrophobic biocompatible ABC triblock terpolymers with different molecular weights of the PCL block (herein referred to as MPEO44-b-PEtOx263-b-PCL87, MPEO44-b-PEtOx263-b-PCL175, MPEO44-b-PEtOx263-b-PCL262) were successfully synthesized by a three-step pathway using a combination of living cationic and anionic ring-opening polymerization (ROP). First, α-methoxy-ω-hydroxy-poly(ethylene oxide) (MPEO) was end-capped with p-toluenesulfonyl chloride. ω-Tosyl-MPEO was used in the second step as a macroinitiator for the ROP of 2-ethyl-2-oxazoline (EtOx) to form the diblock copolymer, MPEO-b-PEtOx. Finally, the prepared diblock copolymer was used as a macroinitiator for the design of the PCL block by ROP of ε-caprolactone (ε-CL). Properties of the newly obtained compounds (macroinitiator, AB diblock and ABC triblock terpolymers) were assessed by 1H NMR and FT-IR spectroscopy and SEC analysis. The selected MPEO44-b-PEtOx263-b-PCL87 triblock terpolymers self-assembled under buffer-simulated physiological conditions into nanoparticles, which were fully characterized by static and dynamic light scattering, nanoparticle tracking analysis and cryo-transmission electron microscopy (cryo-TEM). The combination of the scattering methods revealed a temperature-induced aggregation driven by hydrogen bonding with the LCST approximately between 56 and 60 °C.