The aim of this work is to investigate if size and morphology of nanoparticles can be controlled by changing the hydrophilic ratio of the amphiphilic polymers, changing polymer concentration or simply by changing the preparation method of the particles. An amphiphilic diblock, methoxy poly(ethylene oxide)-block-polycaprolactone (PEO-PCL), with various lengths of the hydrophobic block was utilized. For accurate control of the preparation, a stopped flow apparatus (SFA) was used. The controlled co-solvent method was used for preparation of the final micelles with THF as the organic solvent. Therefore it is also natural to investigate how remaining solvent, specifically in the core, could affect the micelle, and to develop a good method for gently and effective removal of the organic solvent. Small angle X-ray scattering (SAXS) was used to measure size, aggregation number, amount of solvent in the core and radius of the micelles. The SAXS analysis also required complementary measurements of density, size, hydrophilic ratio, molecular weights, polydispersity and crystallinity. In order to obtain a complement and facilitate a thorough SAXS analysis, other measurements were performed using nuclear magnetic resonance (NMR), dynamic light scattering (DLS), densitometry, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). For the difference in polymer concentrations, 1wt% and 0.5wt%, no structural differences are observed, but by changing the block lengths of PCL from 2kDa to 4kDa an increased size and aggregation number were found. No crystallization was detected by DSC or density measurement; hence the core of the micelle in this work is amorphous. For the polymer with 2kDa PCL length, no structural effects were seen as the mixing rate was increased, hence the micelle is dynamic and in equilibrium. However, for the polymer with 4kDa PCL length, a structural change was observed for increasing mixing rate. The length of the hydrophobic block is casing the energy barrier for unimer release so high that the micelles will not gain equilibrium through unimer exchange. The micelles are in a frozen, non-equilibrium state.