Homopolymer induced aggregation of poly(ethylene oxide)n-b-poly(butylene oxide)m polymersomes

We have studied the addition of poly(ethylene oxide) homopolymer (PEO) to a range of polymersome dispersions composed of amphiphilic di- and triblock copolymers. A number of E(n)B(m) E(n)B(m)E(n) and B(m)E(n)B(m) (E = poly(ethylene oxide) B = poly(butylene oxide)) block copolymers of varying molecular weights that spontaneously form polymersomes in water were investigated. This resulted in the aggregation of the dispersed polymersomes by two mechanisms, PEO adsorption or depletion interactions, and is shown to be dependent on PEO concentration. The aggregation kinetics and the resultant structures were analyzed by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). There is a critical relationship between the polymersome corona thickness t and the PEO radius of gyration R(g), where R(g) must equal t to induce aggregation. This phenomenon has been reported with small self-assembling surfactants such as sodium dodecyl sulfate, but here we show an insight into how this transposes into much larger block copolymer systems which show great promise as biomimetic delivery vectors for controlled release.