Hyperbranched polyalkoxysiloxanes, synthesis, characterization and applications (2008)

This dissertation is concerned with the synthesis and characterization of different monomeric and polymeric alkoxymetallates like siloxanes and titanates. These polymers are used as precursors for ultrahydrophobic coatings and inorganic-organic composites of polypropylene and sulfonated polyetheretherketone. The properties of these materials in terms of possible applications are discussed. Different hyperbranched polyethoxysiloxane polymers using triethoxysilanol and acetoxytriethoxysilane as AB3 type monomers were synthesized. Beside of using AB3 monomers, it was possible to synthesize hyperbranched polyethoxysiloxanes also via a titaniumalkoxide catalyzed reaction of tetraethoxysilane with acetic anhydride in a one pot reaction. Polyethoxysiloxanes are liquids and soluble in organic solvents. NMR and MALDI-ToF-MS analysis showed that the polymers obtained by the silanol route have a hyperbranched structure with some cycle formation. Rather similar polymers could be synthesized by the acetoxyroute, which is technologically much more feasible. For these polymers 29Si NMR indicates a less branched structure, which was however not confirmed by the [eta]/Mn values. The synthesis via acetoxytriethoxysilane allows furthermore a distinct control of the molar mass of the polyethoxysiloxane. The products obtained via this route still contain acetoxygroups after short reaction times, but the amount decreases with longer times. Using the titanium catalyzed one pot reaction it was possible to synthesize large amounts in short time. The molecular structure and molar mass of this polymers are very similar to that obtained via the silanol route and the polymer do not contain any acetoxygroups. This synthesis route seems to have a great potential for large scale production of polyethoxysiloxanes. Compared to ´ethylsilicates´ synthesized via hydrolysis and condensation of tetraethoxysilane the polymers synthesized here do not contain any hydroxygroups. The products are stable and low molar mass volatile fractions can be eliminated fully. This was shown by stripping using different procedures. By thin layer short path distillation it was shown that low molar mass compounds can be removed very effectively. Methods like normal vacuum distillation at higher temperatures, where the polymers stay for prolonged time at high temperatures result in cross linking reactions, while at least tetraethoxysilane evolves. Using these methods the molar mass and the viscosity can be increased very effectively, but also the molecular structure changes due to the cross linking reactions. Nevertheless all products obtained were soluble in organic solvents. Therefore stripping of polyethoxysiloxane is a versatile tool to further decrease the amount of volatile compounds in the polymer together with the option to increase the viscosity up to five orders of magnitude and to increase the silica equivalent content up to 59 wt.-%. Further polymers synthesized and discussed in this thesis are polyorganoalkoxysiloxanes using different reaction pathways depending on the monomer used. The studies performed in this work show that (i) hyperbranched polyalkoxysiloxanes can be synthesized rather easily. Especially the one pot synthesis using acetic anhydride in combination with a catalyst seems to have great potential for large scale production. (ii) The polymers synthesized are valuable precursors in all fields of sol-gel chemistry and inorganic-organic composite materials. For the future a huge field of research has been opened regarding the synthesis of hyperbranched precursors polymers for other metal oxides and mixed metal oxides and applications thereof.