Sol-gel chemistry: evidence of redistribution at silicon atom induced by NaOH as catalyst during ageing

The influence of the ageing conditions on the properties of organic-inorgan ic hybrid solids obtained by sol-gel route using NaOH catalysis has been st udied. The cases of 1,4-bis(trimethoxysilyl)benzene 1 ('rigid' precursor) a nd 1,4-bis(trimethoxysilylethyl)benzene 2 ('more flexible' one) have been i nvestigated. The Si-29 CP MAS NMR spectra of the silsesquioxanes clearly re veal that Si-O-Si bond cleavage and redistribution reactions occur when age ing time is increased or is performed at higher temperatures. This particul ar behaviour observed only with NaOH is of importance in the choice of the catalyst. (C) 2001 Academie des sciences / Editions scientifiques et medica les Elsevier SAS.