Controlled Formation of New Si-Based Polymeric Materials

Abstract

<p> This thesis provides examples of new Si-based polymeric materials in three parts. The rapid evolution of hydrogen gas was observed after the combination of an α- or β-hydroxy carboxylic acid with an alkoxyhydrosilane. This unusual reactivity is interpreted to arise from the cooperative nucleophilic attack of the hydroxy group at silicon and the electrophilic attack of the acid proton at the Si-H bond. These systems further react to produce modified sol-gel materials in which the acid units were incorporated into the matrix.</p> <p> The reactions of tetraethoxysilane, (TEOS) and α-hydroxy acids similarly produced modified sol-gels (in solution, DMSO) and solids (precipitated from THF). The reaction kinetics were followed in these systems using 29Si NMR. Extensive characterisation of our sol-gels was carried out by the use of various NMR techniques, FT-IR, elemental analysis and thermal methods of solids characterisation (TGA, DTA, and DSC).</p> <p> Silicones containing vinylsilane units were prepared in order to examine the silicon β-effect in a polymeric system for the first time. The addition of bromine to these systems unexpectedly resulted in no reaction unless vigorous conditions were used. Steric factors as shown by molecular modeling are attributed to this lack of reactivity. Although many silicone systems were studied where more sterically "open" vinylsilanes were present these steric problems could not be overcome.</p>