Search

Summary Adhesion promoters are used to improve the adhesion of liquid‐applied polymeric materials to fillers and substrates. They accomplish this task by replacing the interface with a gradual transition phase (interphase). Organofunctional silanes and oligomeric siloxanes are a technically particularly important class of adhesion promoters. The first part of this two‐part article series deals with the function and structure, the chemistry, and the structure‐property relationships of organically functionalized silane coupling agents. In particular, the partial reactions of hydrolysis, intermolecular self‐condensation (oligomerization), hydrogen bonding and condensation with substrate or filler as well as reaction with the organic polymer are discussed. [ABSTRACT FROM AUTHOR]

Summary Reactivity and properties of many silicon and titanium compounds are very similar. The mostly molecular compounds MX4 (M = Si, Ti; X = electronegative substituent) hydrolyse very rapidly to give silicon/titanium‐oxygen compounds. SiO2 and TiO2 can be prepared by the same processes (precipitation from aqueous solutions, flame hydrolysis, sol‐gel processes) and are insoluble or hardly soluble in acids. Silicates and titanates are formed when the oxides are reacted with bases. Because of the higher reactivity of titanium compounds towards water, different strategies have to be used for the preparation of organically modified derivatives of oxidic compounds. The greatest differences in the chemistry of silicon and titanium are found in the structures of analogous compounds and can mainly be traced back to the greater radius and lower electronegativity of titanium atoms. Titanium prefers octahedral coordination for this reason, but silicon tetrahedral coordination. The different possibilities to connect tetrahedral and octahedral building blocks with each other result in different construction principles of solid state structures. The latter are discussed for oxygen compounds as examples, such as the oxides, silicates/titanates and oxidic cage compounds. [ABSTRACT FROM AUTHOR]

Summary: Sol‐gel processing for the preparation of materials with an basic oxidic structure is a method, which is technically easy (mixing – waiting – processing – drying). Detailed chemical knowledge is necessary, however, if one wants to achieve the optimal materials properties and to exploit all possibilities the method is offering („better materials through chemistry“). The reason is that the gel synthesis proceeds under kinetic control. The obtained materials are therefore amorphous and metastable. Each parameter influencing the reaction rates of precursors or intermediates thus influences structure and properties of the gels and must be carefully controlled. The chemical composition of the gels can be nearly deliberately adjusted by the proper combination of precursors. This affords the possibility to influence materials properties purposefully and to produce demanding “tailor‐made” materials. [ABSTRACT FROM AUTHOR]