About the methods of preparation of poly(ethylene oxide)-b-poly(ε-caprolactone) nanoparticles in water: Analysis by dynamic light scattering

Self-assembly of nonionic amphiphilic poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-b-PCL) and poly(ethylene oxide)-b-poly(γ-methyl-ε-caprolactone) (PEO-b-PMCL) has been studied in water by dynamic light scattering (DLS). The aqueous solutions have been prepared by three methods, i.e., dialysis of solutions in a common organic solvent against water, rapid addition of water to organic solutions, and rapid addition of organic solutions into water. Several common organic solvents have been used: tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethylsulfoxide (DMSO). The dialysis method is not reproducible and leads to very large and polydispersed particles (∼1 μm). In contrast, nanoparticles are formed by the two other methods with a low polydispersity and a size in the 30–100 nm range, depending on the organic solvent used. The particle size increases when the concentration in the organic solvent is decreased. The effect of temperature and length of the hydrophobic block has also been studied.