Herein, we provide a direct proof for differences in the micellar structure of amphiphilic diblock and gradient copolymers, thereby unambiguously demonstrating the influence of monomer distribution along the polymer chains on the micellization behavior. The internal structure of amphiphilic block and gradient co poly(2-oxazolines) based on the hydrophilic poly(2-methyl-2-oxazoline) (PMeOx) and the hydrophobic poly(2-phenyl-2-oxazoline) (PPhOx) was studied in water and water-ethanol mixtures by small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), static and dynamic light scattering (SLS/DLS), and 1H NMR spectroscopy. Contrast matching SANS experiments revealed that block copolymers form micelles with a uniform density profile of the core. In contrast to popular assumption, the outer part of the core of the gradient copolymer micelles has a distinctly higher density than the middle of the core. We attribute the latter finding to back-folding of chains resulting from hydrophilic-hydrophobic interactions, leading to a new type of micelles that we refer to as micelles with a "bitterball-core" structure.

A 5 Shubnikov Institute of Crystallography Federal Scientific Research Centre 'Crystallography and Photonics' Russian Academy of Sciences Leninsky prospekt 59 Moscow 119333 Russian Federation

Department of Organic and Macromolecular Chemistry Ghent University Krijgslaan 281 S4 9000 Ghent Belgium

Forschungszentrum Jülich GmbH Jülich Centre for Neutron Science JCNS Outstation at Heinz Maier Leibnitz Zentrum Lichtenbergstraße 1 85748 Garching Germany

Hamburg Outstation European Molecular Biology Laboratory c o DESY Notkestrasse 85 Hamburg 22607 Germany

Institute of Macromolecular Chemistry Academy of Sciences of the Czech Republic CZ 162 06 Praha 1 Czech Republic

Institute of Physics Academy of Sciences of the Czech Republic 182 21 Praha 8 Czech Republic

ISIS Facility STFC Rutherford Appleton Laboratory Harwell Oxford Didcot OX11 0QX United Kingdom

National Research Centre Kurchatov Institute Akademika Kurchatova Place 1 Moscow 123182 Russian Federation

National Research South Ural State University Chelyabinsk 454080 Russian Federation

Physics Department Lomonosov Moscow State University Moscow 119991 Russian Federation

Technische Universität München Physik Department Fachgebiet Physik weicher Materie James Franck Straße 1 85748 Garching Germany

References provided by Crossref.org

Cationic Ring-Opening Polymerization-Induced Self-Assembly (CROPISA) of 2-Oxazolines: From Block Copolymers to One-Step Gradient Copolymer Nanoparticles

Influence of Hydrophobic Side-Chain Length in Amphiphilic Gradient Copoly(2-oxazoline)s on the Therapeutics Loading, Stability, Cellular Uptake and Pharmacokinetics of Nano-Formulation with Curcumin