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B. Froschauer:
"Modifizierung von Melamin und Schichtsilikaten zur Herstellung von Nanocomposites auf Basis von Melaminharzen";
Betreuer/in(nen), Begutachter/in(nen): H. Gruber, F. Kubel; E163 Institut für Angewandte Synthesechemie, 2003.

In the present work various salts derived from melamine and organic acids were prepared in homogeneous reaction. The resulting salts formed on cooling were characterised by 1H-, 13C- and 15N-NMR spectroscopic measurements. Another major focus was dedicated towards the thermal analysis of melamine salts derived from organic acids with respect to their flame retardant. The thermal behaviour of the salts was investigated by TGA and DSC. In most cases a loss of weight about 7% was detected at 100-150°C indicating evolution of water, and at 220-320°C 90% of the residual salt was decomposed. Thus the thermal behaviour was in a good agreement with commercial flame retardant products. The crystal structure of the melamine salts, especially the identification of the protonation site of the melaminium cation, was investigated by X-ray studies demonstrating that the endocyclic nitrogen atoms are more basic than the exocylic nitrogen atoms. The conversion of melamine salts to amides or imides was also investigated by direct heating of the salts but only in two cases a small yield of amide and imide were obtained by reacting the salts under microwave. Melamine was also reacted with acid anhydrides of organic acids such as succinic, benzoic- and maleicacid anhydride yielding Melamine succinamide, -imide and benzoic amide respectively. In the second part of the work, the preparation of nanocomposites based on montmorillonite and melamine resin was investigated. Montmorillonite was modified with compatibilizing agents like alkylammonium ions or silanes to increase the layer distance, thus decreasing the interfacial energy between the polar silicate and the hydrophobic polymer matrix. Incorporation of triethyl- hexadecyl- and octadecylammonium ions resulted in an increased spacing between the clay layers by the length of the alkylammonium ions by about 100%. In addition, Aminopropyltriethoxysilane (APTS), Methyltrimethoxy- and Trimethylmethoxysilane were used as coupling agents for covalent bonding to the surface of montmorillonite. Evaluation of chemical bonding by 29Si-NMR-spectroscopy through integration Q3[HO-Si(OM)3]/Q4[Si(OM)4] demonstrated only a small yield of APTS bonded to surface. Furthermore, melamine resins reacted with silanes and characterized by 1H- and 13C- and 29Si-NMR-spectroscopic measurements. The major reaction resulted in the loss of -OH and -OCH3 groups in the resin to ether crosslinks to the silane. Finally the compounding of melamine resin and modified montmorillonite was investigated to obtain materials in which the silicate layers are distributed on a nanometer-scale and with high aspect ratio. The nanocomposites were prepared by blending the moulded resins with APTS modified and alkylammonium ion exchanged montmorillonite yielding composites with exfoliated structures. The preparation of the composites in solution yielded intercalated structure in polar and exfoliated structure in non polar solvent. Mechanical properties were studied by intercalated APTS-MM in melamine resin but no improvements of mechanical strength were observed.