Organoalkoxysilane condensation

Consider a trialkoxysilane as co-precursor for an initial 1 1 mixture of alkoxysilane and organoalkoxysilane, and recall that in the case of ORMOSIL condensation takes place only through elimination of water27 and not by alcohol formation. The mechanism involves hydrolysis and condensation reactions ... 

These polysiloxanes were also found to be synthesized by the condensation reaction between organosilanes and organoalkoxysilanes with release of alkane as an inert by-product. For this polycondensation, B(C6F5)3 was used as an effective catalyst [88]. This process involves cleavage of C-0... 

OTES is currently the most promising organoalkoxysilane for use as a water repellent [18 - 20]. For the determination of optimum conditions for the use of OTES, its HPC processes have to be investigated under various conditions. However, there is a lack of literary data concerning the processes of OTES condensation and hydrolysis. Therefore, this pq)er deals with the investigation of OTES HPC for electrophilic catalysis. 

The rate-constant results [62,86] suggest that as the size of the alkoxide substituents increases or, as the reacting species become more highly condensed, steric effects become increasingly important as observed, for example, in organoalkoxysilanes [47]. 

It is generally agreed that both hydrolysis and condensation occur by adder base-catalyzed bimolecular nucleophilic substitution reactions involving, e.g., Sf Z-Si, S 2 -Si, or S 2 -Si transition states or intermediates. The acid-catalyzed mechanisms are preceded by rapid protonation of the OR or OH substituents bonded to Si, whereas under basic conditions hydroxyl or silanolate anions attack Si directly. Statistical and steric effects are probably most important in influencing the kinetics however. Inductive effects are certainly evident in the hydrolysis of organoalkoxysilanes. 

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