Inorganic matrices hydrolysis reactions

The sol-gel chemistry has also been used to prepare inorganic inhomogeneities in an organic matrix. Silane end-capped macrodiols can be used. Hydrolysis and condensation of alkoxy silane groups lead to inorganic hard clusters (Fig. 7.6b). Intramolecular reactions and the miscibility of the soft-segment chains with the relatively polar crosslinks determine the size distribution of the clusters (nanofillers). 

The sol-gel process performed in low concentrated polymer-solvent solutions is another attractive route to develop hybrid membranes because it allows an in situ dispersion of metal-based nanoparticles within the polymeric matrix, achieving a suitable interfacial morphology between the continuous and the dispersed phase. Silica particles and polyimide have been frequently used to produce these hybrid membranes [107,108]. In general, hydrolysis and condensation reactions are involved in the sol-gel process, when alkoxides are involved in the formation of the dispersed phase. The advantage of using this method is the formation of an inorganic network largely interconnected with the polymeric materials mainly with noncovalent interactions [109]. In Fig. 7.10 a... 

The sol-gel synthesis of hybrid materials involves the occurrence of hydrolysis and condensation reactions in the presence of an organic polymer. Obviously, the selection of suitable polymer is of fundamental importance for the synthesis of the hybrid materials, as it should exhibit good miscibility with typical sol-gel precursors. The presence of suitable functional groups can facilitate the linkage between the polymer and the inorganic component. Also, the nature of the polymeric matrix is important because different properties of the matrix and, consequently, of the resulting nanohybrid material can be addressed for instance, the polymeric marix can be an elastomer (as in the case of polydimethylsiloxane) or thermoplastic (e.g., polytetrahydrofuran), amorphous, or (partially) crystalline [81]. 

The sol-gel process has provided promising opportunities for the preparation of a variety of organie-inorganie hybrid materials at the molecular level. The in-situ development of a three-dimensional cross-linked inorganic network structure using an organie preeursor sueh as an alkoxide, M(OR)4, can be carried out within the polymer matrix. The hydrolysis and condensation reactions involved in the proeess may proceed as follows ... 

---