Hannover, Universiẗat, Diss., 2000.

Halle, Wittenberg, University, Diss., 2003.

Tübingen, Universiẗat, Diss., 2000.

Hannover, Universiẗat, Diss., 2002.

Heidelberg, Universiẗat, Diss., 2001. / Dateiformat: tgz, Dateien im PDF-Format.

Mainz, Universiẗat, Diss., 2003.

University, Diss., 2001--Tübingen. / Text engl.

<p> Synthesis of new biocompatible siloxane surfactants, where hydrophobic siloxanes are modified by biocompatible hydrophilic functional groups (e.g., triethoxysilane (TES), polyethylene glycol (PEO), and carboxylic acid) is a research area of increasing interest. In this research project we have developed a new class of these biocompatible surfactants, based on siloxanes, as the hydrophobic part, and boronic acids as the hydrophilic part. The reasons for choosing boronic acidlboronates as a modifying agents include: their pH sensitivity, biocompatibility, possible interactions with sugars, and because of a broader general utility in synthesis. The promise of these properties combined with the hydrophobicity, flexibility and many other important features of siloxanes encouraged us to initiate these syntheses. </p> <p> We have explored different synthetic strategies to prepare siloxane boronic acid surfactants, including Grignard reactions and metal-catalyzed hydroboration reactions. Nevertheless, the main approach that was investigated is metal-catalyzed hydrosilylation reactions of vinylphenylboronic acid. Two different approaches were developed to prepare the target compounds: (1) metal-catalyzed hydrosilylation using non-protected vinylphenylboronic acid and (2) metal-catalyzed hydrosilylation using protected vinylphenylboronic acid that can be removed under gentle conditions. The protected compounds underwent hydrosilylation smoothly, but led after separation using column chromatography to the unprotected compounds in moderate yield. The conversion of the hydrosilylation of unprotected boronic acids was quite good, but the compounds underwent decomposition during chromatography. Thus, the two approaches are complementary, depending on whether pure molecules are required for further synthetic elaboration, or a mixture of materials is suitable for practical application as surfactants. </p> <p> The amphiphilic nature of these siloxane boronic acid surfactants was studied and the compounds were found to be surface active. The limited solubility of our compounds in H20 prevented us from studying their surface tension properties. However, their solubility in chloroform enabled us to study their interfacial properties. </p> / Thesis / Master of Science (MSc)

No description available.

Abstract Two novel conjugated polymers (PTP-SiO) and (PTP-P-SiO) with alternating N-containing heterocycles and siloxane (-Si-O-) units were synthesized using the Heck reaction. The incorporation of siloxane units in the polymers improves their thermal stability and processability. The polymers can be dissolved in organic solvent and exhibited good thermal stability with 5¢H weight loss temperature above 370¢J under nitrogen atmosphere. The photoluminescence (PL) spectra of PTP-SiO and PTP-P-SiO in solution show maximum peaks at 491 and 520 nm respectively. The heterocycles in the two polymers contain N- atoms, which can coordinate with transition or lanthanides metal ions to form complexes. The absorption spectra show peaks at around 275~290 nm and 320~330 nm, which are attributed to £k-£k* and n-£k* transitions, respectively. On the other hand, the emission spectra consist of peaks at around 408~420 nm and 491~520 nm. These two emission peaks belong to £k-£k* and n-£k* transitions of the ligands, respectively. With pyridazine ( heterocycle with ¡VN=N- group) ring, PTP-P-SiO shows more significant variation upon coordination with metals ions as compared to PTP-SiO. These variations of optical property offer a possibility for application in chemosensors for detection of metal ions.