Complex Self-Assembly Behavior of Bis-hydrophilic PEO-b-PCL-b-PMOXA Triblock Copolymers in Aqueous Solution

We report aqueous self-assembly of linear amphiphilic triblock copolymers poly(ethylene oxide)-block-polycaprolactone-block-poly(2-methyl-2-oxazoline) (PEO-b-PCL-b-PMOXA) and their PEO-b-PCL precursors with different PCL and PMOXA block lengths using three preparation methods: film rehydration, solvent evaporation, and cosolvent. For PEO-b-PCL, the self-assembled structures were ordinary spherical particles and polymersomes. For PEO-b-PCL-b-PMOXA, we observed polymersomes with asymmetric membrane, cloud-like aggregates, elongated particles, Y-shaped elongated particles, and 3D networks. All structures were of micrometer size and characterized using laser scanning microscopy (LSM). 3D networks were also characterized using z-stack confocal LSM, transmission electron microscopy (TEM), and cryogenic TEM. We demonstrated that film rehydration method results in pseudoequilibrium structures, whereas structures formed using solvent evaporation and cosolvent methods are under kinetic control. We showed how kinetically controlled structures can be transformed into pseudoequilibrium morphologies.