In solution, THF is a very good solvent for the PS block, while the solubility of P4VP is quite low. For PS-b-P4VP dBCPs with a notably lower P4VP fraction with respect to that of the soluble PS block, spherical micelles with an insoluble P4VP core and a soluble corona made of PS blocks will be formed. Raising the fraction of the less soluble P4VP block alters the packing parameter of the dBCP chains, which can lead to a morphological transition to rods, worm-like micelles, or vesicles (top of Scheme 1). The size and shape of the micelles formed by the five new diblock copolymers were characterized both in the dry state and in THF dispersion by TEM, DLS, and cryo-TEM. It is expected that they only show spherical micelles since the P4VP part is still too small (< 80%) for the formation of rods or worm-like micelles. Due to the higher contrast, the crystalline P4VP core appears dark in the TEM pictures in Figure and Figure with the PS shell in light gray. In fact, only spherical micelles were found by TEM measurements for all dBCPs. The diameter of the insoluble P4VP cores (Dcore) of the micelles increases continuously starting at 15 nm ± 2 nm for SV-15 and reaching 73 nm ± 9 nm for SV-61 (Table and Figure ). In addition, narrow hydrodynamic diameter distributions were detected for all diblock copolymer micelles by DLS (Figure ). At first, the measured hydrodynamic diameters (Dh) of the dBCPs correlate with both the molecular weight and the P4VP fraction. The hydrodynamic diameters start at 75 nm ± 28 nm for SV-15 and increase with the P4VP fraction up to 125 nm ± 34 nm for SV-42. Although having the highest molecular weight and P4VP content of all analyzed dBCPs, SV-61 does not show the largest hydrodynamic diameter. Instead, it is similar to SV-42 with 119 nm ± 29 nm (Figure and Figure ), which can be explained with the reduced PS chain length, which also influences Dh. The dBCPs were also imaged by cryo-TEM to evaluate the micelle size and shape in solution, which is important for their use as nanoreactor. Please note, due to the higher electron density contrast of the insoluble P4VP core, the soluble PS corona is hardly visible. Again, spherical micelles were found for all five neat dBCPs and diameters ranging from 26 nm ± 2 nm for SV-15 to 71 nm ± 4 nm for SV-61 were measured (Table ).