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Polystyrene-block-polyglycidol Micelles Cross-Linked with Titanium Tetraisopropoxide. Laser Light and Small-Angle X-ray Scattering Studies on Their Formation in Solution

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journal contribution
posted on 16.11.2010, 00:00 by Melanie Siebert, Artur Henke, Thomas Eckert, Walter Richtering, Helmut Keul, Martin Möller
Hybrid micelles from polystyrene-block-polyglycidol (PS-b-PG) copolymers with chemically cross-linked cores by titanium tetraisopropoxide (Ti(OC3H7)4) were prepared in toluene solution. Additionally, micellization of PS-b-PG copolymers with different mass fractions of polyglycidol (xPG), was studied by static and dynamic light scattering as well as small-angle X-ray scattering. It was observed that copolymers with xPG smaller than 0.5 self-assembled in toluene into spherical core−shell micelles with hydrodynamic radii Rh between 12 and 23 nm. On the other hand, copolymers with larger PG content formed particles with Rh = 50−70 nm and aggregation numbers of several thousands. The presence of these aggregates in solution was attributed to the nonequilibrated form of block copolymers upon dissolving, most probably due to hydrogen bonding. In the following, spherical PS-b-PG micelles were loaded in toluene with hydrochloric acid and titanium tetraisopropoxide. Confined hydrolysis of Ti(OC3H7)4 induced by HCl in the micellar core was confirmed by small-angle X-ray scattering experiments. The subsequent condensation of the precursor with hydroxyl groups of polyglycidol chains led to covalently stabilized hybrid organic−inorganic particles. The presence of cross-linked PS-b-PG micelles was proven in two ways. First, micelles with “frozen” core showed stable hydrodynamic size in time upon dilution below critical micellization concentration while non-cross-linked PS-b-PG micelles underwent disintegration under the same conditions within several hours. Second, light scattering experiments revealed the presence of stable, swollen particles in N,N-dimethylformamide, which is a good solvent for both blocks.