Synthese von mono- und multi-funktionalisierten Polysiloxanen und deren Charakterisierung hinsichtlich der Adhäsion auf Modelloberflächen und Humanhaar

• Synthesis of mono- and multi-functionalized polysiloxanes and their characterization regarding the adhesion on model substrates and human hair

Heedfeld, Robin Ruben; Möller, Martin (Thesis advisor); Pich, Andrij (Thesis advisor)

1. Auflage. - Aachen : Verlagsgruppe Mainz GmbH Aachen (2021)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur Chemie 132
Page(s)/Article-Nr.: xiv, 163 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

It was the goal of this thesis to synthesize mono- and multi-functionalized polysiloxanes and to investigate their properties. Therefore, an adequate synthesis strategy has been developed. First an equilibrium reaction was carried out to obtain linear hydrogen functionalized polysiloxanes. In a following reaction these polymers were converted with allyl glycidyl ether into epoxy functionalized polysiloxanes. These materials are considered as platform chemicals for further functionalization. It has been proofed, that the epoxy group can react with different amines and carboxylic acids. Herewith the following functional groups were bound to the polysiloxane backbone: Thioester, azetidinium, catechol, phenol, quaternary amine, imidazolidinon and indol. Including the hydrogen and epoxy functionalized polysiloxanes, in total 63 mono-functionalized polysiloxanes were synthesized and described in this thesis. Further it was investigated how multi- functionalized polysiloxanes can be synthesized with the described approach. These multi-functionalized polysiloxanes are of particular interest, because their structure (functional groups in combination with the flexible polysiloxane backbone) resembles with the structure of proteins. In this thesis bis-, tris- and tetrakis-functionalized polysiloxanes were synthesized and analyzed, in total 22 multi-functionalized polysiloxanes. For ionic amphiphilic polysiloxanes an efficient way of purification was described by salting out these polymers. Parts of this thesis contributed to a patent, filed under the number US 2017/0291994 A1. The water solubility of the obtained functionalized polysiloxanes was measured via 1H-NMR. For the water soluble ionic polysiloxanes the critical micelle concentration was determined via pendant drop surface tension measurements. Another focus of this thesis was to investigate the film formation of the functionalized polysiloxanes. Therefore, silicon wafers were systematically coated with the obtained functionalized polysiloxanes and the film thickness was measured via ellipsometry measurements. Surprisingly it was shown, that besides the catechol functionalized polysiloxanes also the thioester functionalized polysiloxanes formed stable films. These coatings consist of multilayers of functionalized polysiloxanes. To investigate the adsorption of the first monolayer of a functionalized polysiloxane on a model surface a new method has been developed. Using contact angle measurements of an air bubble, the adhesion of catechol functionalized polysiloxanes on a PMMA surface from an aqueous solution were observed. It was shown that higher molecular weight polysiloxanes adsorb faster on the surface than polysiloxanes with a lower molecular weight. For three different catechol functionalized polysiloxanes a factor has been calculated, that describes the energy win of the adsorption, which characterizes the adhesion. For future investigations a specific sample holder was designed and 3D-printed, which allows to test further organic and inorganic materials. In another chapter of this thesis it is shown, that functionalized polysiloxanes can be used to stabilize nanoparticles and protect them from agglomeration. Transmission electron microscopy images show, that if polysiloxanes are covalent bond to LaB6 Particles, they prevent the particles to agglomerate. In the last part of the thesis it was investigated how and especially where functionalized polysiloxanes can adhere to human hair. The question, if polysiloxanes can infiltrate or adsorb at the hair surface is for the hair care industry of interest. First it was shown with UV/Vis measurements, that human hair releases substances in aqueous solution, which can agglomerate with polysiloxanes. Transmission electron microscopy measurements in combination with an EELS detector show that the infiltration and adsorption of polysiloxanes depends on their molecular weight. A high molecular weight leads to the adsorption on the hair surface. The lower a molecular weight of the polysiloxane is, the deeper it can infiltrate the hair cuticle. It was investigated that the sulfur rich A-Layer is a natural barrier in the infiltration process. The diffusion pathway of the polysiloxanes is via the cell membrane complex of the cuticle. It is observed that, polysiloxanes accumulate in defects of the cuticula. They can diffuse from an aqueous solution into the damaged areas inside the hair. This mechanism of the polysiloxanes can be named as a hair-repair process.