Silicon-based organic and inorganic polymers

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Virginia Tech

The range of polymeric materials containing the Si-O bond spans from the three-dimensional inorganic networks of silica (SiO₂), to linear high molecular weight polysiloxanes which display properties of both organic and inorganic materials.

Part 1 of this dissertation describes the synthesis of three-dimensional inorganic SiO₂ networks and organic-inorganic hybrid networks using a low temperature solution technique known as the sol-gel process. During this process, hydrolysis and subsequent condensation of inorganic alkoxides (most often tetraethylorthosilicate, TEOS) in the presence of catalysts leads to the formation of three-dimensional SiO₂ networks. However, the strong acid or base catalysts typically employed in sol-gel reactions would also cause undesirable degradation of many organic modifiers, especially at higher temperatures required for the drying of the gels.

A catalyst-free sol-gel process, based on tetramethyl orthosilicate (TMOS), the most reactive silicon tetra alkoxide in the series, was developed. The catalyst-free route provides an optimum reaction environment for the synthesis of organic-inorganic materials through copolymerization reactions. This concept will be exemplified by two organic-inorganic systems in which TMOS was used as the inorganic component while poly(dimethylsiloxane) and polyimide oligomers respectively, were employed as the organic component. The effect of such modifications on the surface and bulk properties of the inorganic SiO₂ networks was also investigated.

Part 2 of this dissertation describes specific aspects associated with the synthesis of amine containing polysiloxane oligomers. A new molecular design which allows for independent control of molecular weight and amine functionalities was developed. The new synthesis involves anionic ring opening equilibrium copolymerization of the cyclic siloxane tetramer D₄ with a new cyclic siloxane monomer containing amine functionalities as pendant groups on silicon atoms. The effect of the bulky substituent {-CH₂CH(CH₃)CH₂NHCH₂CH₂NH₂} of the silicon atom on the position of thermodynamic equilibrium, and the extent of molecular weight and composition control in the linear polysiloxane oligomers was studied.