Polymersome formation induced by encapsulation of water-insoluble molecules within ABC triblock terpolymers

Polymeric micelles have been extensively studied as nanoscale drug carriers. Knowing how the encapsulation of drugs alters the micellar structure is one of the most important issues for the biomedical application of amphiphilic block copolymers. However, little is known so far about the structural changes that micelles undergo upon loading with water-insoluble guests. Herein, we investigate the micellar morphology of ABC triblock terpolymers after loading with various water-insoluble molecules (naphthalene and its derivatives as drug-equivalent model molecules). The triblock terpolymer features a poly(ethylene oxide) (PEO) block, a poly(allyl glycidyl ether) segment which has been functionalized with carboxylic acid moieties (PAGECOOH), and poly(tert-butyl glycidyl ether) (PtBGE) as a hydrophobic block. Structural analysis by small-angle X-ray scattering (SAXS) and cryogenic and conventional transmission electron microscopy (TEM) found that a morphological transition from spherical micelles to vesicles (polymersomes) was induced by loading the guest molecules at pH 4, whilst the spherical and prolate morphologies remained unchanged upon loading at pH 6 and 8. This study highlights the dynamics and morphological changes of polymeric micelles upon loading with guest molecules.