Vesicle Formation of PLAx−PEG44 Diblock Copolymers

Three PLAx−PEG44 diblock copolymers with fixed hydrophilic PEG block and various lengths of hydrophobic PLA block were synthesized via ring-opening polymerization. The micelle formation and micelle morphologies of the PLAx−PEG44 copolymers in selective solvents were investigated by using cryogenic transmission electron microscopy (cryo-TEM) and light scattering techniques. PLAx−PEG44 diblock copolymers in aqueous solution form various micelle structures when increasing x from 56 to 212 in order to minimize the overall free energy of the systems. The micelles transform from wormlike micelles for PLA56−PEG44 into vesicles for PLA212−PEG44. Interestingly, vesicular structures with various morphologies, such as large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, ellipsoidal vesicles, open bending lamellae, vesicles with irregular shapes, etc., were found to be coexisting in PLA212−PEG44 THF/H2O and PLA212−PEG44 dioxane/H2O mixtures with 30 and 40 wt % water contents. Toroid micelles w...