Reactive amphiphilic block copolymers for the preparation of hybrid inorganic/organic materials

In this thesis the synthesis of well-defined polystyrene-block-polyglycidol (PS-b-PG) block copolymers, their micelle formation and the use of these micelles for the preparation of hybrid inorganic/organic materials are described. The hybrid materials are used for patterning of highly ordered titanium dioxide nanoparticles on a silicon wafer. The amphiphilic block copolymers were synthesized by sequential anionic polymerisation of the corresponding monomers in benzene with the sec-butyl lithium/phosphazene base initiating system to achieve well-defined polystyrene-block-poly(ethoxy ethyl glycidyl ether) (PS-b-PEEGE) block copolymers. It was shown that chain-transfer reactions during the polymerisation process limit the molecular weight of the PEEGE block and tailing in the SEC traces indicated the presence of PEEGE homopolymer. The removal of the protection group was achieved with concentrated hydrochloric acid or an acidic ion exchange resin. In both cases the deprotection was quantitative, but in case of the hydrochloric acid the reaction conditions played a very important role; under optimal conditions no degradation of the PEEGE block in the copolymer was observed. The PG homopolymer inside the block copolymer was responsible for the tailing in SEC and was removed by precipitation of the block copolymer in distilled water. The glass transition temperatures of PS-b-PEEGE and PS-b-PG were determined by DSC. It could be shown that the PS-b-PEEGE block copolymers were completely miscible proven by only one glass transition temperature. In contrast, the PS-b-PG block copolymers had two glass transition temperatures showing their immiscibility. The PS-b-PG block copolymers were used for the preparation of micellar solutions in toluene as selective solvent. The micelles were characterized by static and dynamic light scattering as well as small angle X-ray scattering. The results of the light scattering experiments showed that copolymers containing a mass fraction of PG block below 0.5 self-assembled into core-shell micelles, while samples with higher PG content formed non-specifically aggregated particles. Their presence resulted most probably from multiple hydrogen bond formation between PG units that could strongly restrict their complete equilibration in solution. Additionally, the micellar solutions of PS-b-PG block copolymers were coated onto mica as substrate. It could be shown by SFM and TEM that the dried micelles had mostly a spherical shape. The well-defined core-shell micelles of PS-b-PG were loaded with concentrated hydrochloric acid and titanium(IV) isopropoxide (titanium alkoxide) which lead to hydrolysis of the titanium alkoxide within the micellar core. It was proven that a condensation reaction lead to a permanent connection between glycidol units and the inorganic component. As a consequence, stable hybrid micelles were obtained, which were coated onto a substrate to form a thin film and analyzed again by SFM and TEM. The cross-linked micelles were used for the highly controlled nanostructuring of titanium dioxide on the surface. The titanium-loaded micellar solutions were coated onto a silicon wafer to obtain thin films. These thin films were treated with hydrogen plasma to remove the organic material and convert the titanium alkoxide to well-defined titanium dioxide nanoparticles. The hexagonal ordering of titanium dioxide was proven by microscopic techniques and X-ray photoelectron spectroscopy confirmed the chemical nature of the particles.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2011

Author dc:creator

• Siebert, Melanie

Contributors dc:contributor

• Möller, Martin

• info:eu-repo/classification/ddc/540
• Polymere
• Polymerlösung
• Micelle
• Nanopartikel
• Vernetzung <Chemie>
• Kraftmikroskopie
• Durchstrahlungselektronenmikroskopie
• Dynamische Lichtstreuung
• Statische Lichtstreuung
• Röntgen-Photoelektronenspektroskopie
• Chemie
• block copolymers
• micelle formation
• metal nanoparticles
• cross-linking
• light scattering

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113889%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51616