Klaus Endres

Inorganic-organic polymers derived from functional silicic acid derivatives by additive reaction

Abstract Inorganic-organic polymers were synthesized by additive reaction of vinyl-, allyl-, and H-silylated double four-ring (D4R) silicic acids and polymeric silicic acids. The structure and properties of the hybrid polymers were investigated by means of 29Si NMR spectroscopy, thermoanalysis and BET nitrogen adsorption measurements. Using the defined vinylsilylated D4R silicicacid [(CH2CH)(CH3)2Si]8Si8O20 and the corresponding H-silylated compound [(CH3)2HSi]8Si8O20 as precursors, the additive reaction results in a microporous polymer with a ordered Si8O20 substructure. The structural units are connected by six-membered bridges. Shorter (four-membered) or longer (seven-membered) bridges between D4R cages lead to non-porous polymeric materials. The connection of water-glass-derived silicic acid units by six-membered bridges similarly leads to porous polymers with specific surface areas of 500 m2/g. For the preparation of the porous hybrid polymers a new, simple two-step reaction route is described.

Colored coatings on eye glass lenses by noble metal colloids

Abstract Metal colloids in glass coatings are suitable for preparation of colored transparent coatings with thicknesses of about 0.2 to l μm due to their high molar coefficient of absorbance (≈ 10 6 l/(mol cm)). The absorbance of these metallic particles in a dielectric environment is caused by a surface plasmon resonance effect of the conductive electrons of the colloids. Therefore, it is characteristic for the metal, but can be affected by the dielectric properties of the surrounding matrix. Glass sol—gel coatings have been developed for the preparation of 0.2 to 0.4 μm thick, transparent colored coatings on silicate eye glass lenses by incorporation of Au-, Ag- and Pd-colloids into an 87 mol% SiO 2 —13 mol% PbO glass. A functionalized silane has been used as a complex forming agent for the appropriate noble metal ions to control the nucleation and growth processes of the colloids during the thermal densification of the coatings. By mixing different noble metal salts and addition of Co 2+ ions, pink, brown, green and grey colors with optical densities ≤ 6 have been obtained. By variation of the glass composition the refractive index of the coating can be adapted to that of different types of substrate glasses ( n D from 1.52 to 1.6) to obtain coatings with desirable optical performance. In a similar manner the transformation temperature ( T g ) of the coatings can be less than the substrate, allowing a complete thermal densification of the coatings at about 500°C. The coatings show glass like chemical durability and mechanical stability. Due to the optical and thermomechanical properties of the colored coatings and due to the thermal and UV-stability of the colloids these coatings were applied to eye glass lenses.

New routes to silicic acid containing inorganic-organic hybrid precursors and polymers

In view of the outstanding role that silicic acids (sa.) play in inorganic materials a survey will be presented regarding the possibilities of the integration of sa. in organic matrices via chemical reactions. The objective is to combine the advantageous properties of the silicic acid with those of the organic compounds in order to generate novel materials. The reactions of silicic acids with organic molecules, as studied by 29 Si NMR spectroscopy, are described using the silicic acid H 8 Si 8 O 20 with a defined double four-ring structure as an example. By silylation of the hydrophilic H 8 Si 8 O 20 its functional organophilic derivatives were synthesized. The s.a. derivatives with epoxy-, alkoxy-, HSi-, ketoester or unsaturated groups are capable of condensation, polymerization, complexation or additive reactions leading to reactive inorganic-organic precursors or polymers with the defined silicic acid unit. The synthesis and structure of the following s.a. containing precursors and polymers will be reported, (a) inorganic-organic polymers with a high content of silanol groups, (b) microporous polymers free of silanol groups and (c) metal (Al, Zr) alkoxide complexes attached to defined silicic acid units. The model reactions of the double four-ring silicic acid derivatives can be transferred to technical silicic acid solutions prepared from water glass. The presented reaction pathways are a basis for the preparation of a great variety of new inorganic-organic compounds with tailor-made structures and properties which can be used for highly homogeneous and stoichiometric materials.

Coatings for increasing and preserving the bending strength of glass

The practical strength of glass with a value of about 100 MPa is approximately 100 times smaller than its theoretical ones [1]. This is due to micro flaws on the glass surface, which amount up to 50.000 on one cm2[2]. During the handling of glass externals stresses are amplified by these flaws, like clefts, pores or inclusions [3]. The degree of amplification depends on the geometry of the crack tip, which can be strongly influenced by chemical interactions with the surroundings. Depending on the intensity of these external influences, a rather slow crack propagation is observed under subcritical load (static fatigue). However, when the applied tensile stress exceeds a critical value (Kic-factor) the crack grows spontaneously with almost the speed of sound [4,5], leading essentially to the breaking of the glass.

Development of antireflective coatings for automotive glazing by wet chemical processing

A wet chemical coating technique for dielectric multilayers with antireflective (AR) properties on automotive glazing has been developed. The coating solutions consist of SiO2 and TiO2 nanoparticles of 10 nm and 4 nm respectively in isopropanol which carry epoxysilane surface ligands. Batches of 100 l are prepared in appropriate reactors under controlled conditions. A 4layer AR system is deposited on side 1 and side 4 of an automotive windscreen by dip coating with constant withdrawal speeds. Each single layer is cured for 5 minutes at 120°C. Finally, the whole AR stack is fired at 450°C for 1 h, leading to a homogeneous bluish residual reflectance. The design of the AR stack had been optimized for flat angles of incidence by computer simulation, in order to minimize reflections from the dashboard into the drivers view. Therefore, a residual reflectance of about 2 % to 4 % is obtained for perpendicular incidence in the range from 490 nm to 700 nm wavelength. For an incident angle of 60°, the reflectance is decreased from 15 % (uncoated) to 6 % and for an angle of 65° from 20 % to 10 %. The coatings show the same scratch hardness as uncoated glass in taber abrasor tests, and no degradation is observed in salt water boiling test for more than 11 days and UV test for more than 340 h.

Zum Einfluß von Sol-Gel-Beschichtungen auf die Spannungsrißkorrosion an Floatglasoberflächen

Einleitung und Zielsetzung: Obwohl Glas einer der chemisch resistentesten Werkstoffe ist, treten beim Kontakt mit unterschiedlichen Medien chemische Wechselwirkungen auf. Wie Untersuchungen von Wiederhorn gezeigt haben, wird die Spannungsriskorrosion und damit die statische Ermudung von Glas durch das Zusammenwirken von mechanischer Belastung und Wasser aus der Umgebung begunstigt. Aus dem Stand der Technik ist bekannt, das bei der Herstellung von Glasfasern organische Polymerbeschichtungen eingesetzt werden, um die Diffusion von Wasser und Wasserdampf an die Glasoberflache zu vermeiden. Daneben sind viele Arbeiten aus der Sol-Gel-Chemie bekannt, die sich mit dem Einflus von organischen Beschichtungen auf die Spannungsriskorrosion beschaftigen. Die durchgefuhrten Untersuchungen verfolgten das Ziel, die Mikrorisse in Glasoberflachen durch naschemische Behandlung vor einem korrosiven Angriff durch Wasser zu schutzen. Die Beeinflussung der Lebensdauer sollte anhand von Zeitstandversuchen an geschadigten Glasern nachgewiesen werden, sowie durch Bestimmung der Bruchfestigkeit als Funktion der Lastauftragsrate.

Solid state 29Si NMR investigation of inorganic-organic polymers with defined silicic acid units

By thermal analysis and 29Si NMR spectroscopy the thermal behaviour and structural changes of two different types of inorganic-organic polymers with defined double four-ring silicic acid units (Si8O20) were characterized. Polymer 1, prepared from the organic silicic acid precursors [(CH3)2HSi]8Si8O20 (Q8M8H) and [CH2=CH(CH3)2Si]8Si8O20 (Q8M8V), preserves the double four-ring structure up to 350°C Higher temperatures lead to structural reorganizations of the SiO4 tetrahedra forming at 900°C a structure similiar to amorphous silica. Polymer 2, synthesized by condensation reaction of the new organic silicic acid precursor [CH3O)3Si(CH2)3OC(O)CH(CH3)CH2Si(CH3)2]8Si8O20, shows with 37% uncondensed SiOH groups a remarkable high content of silanol groups caused by sterical hindrances.