The sol-gel polymerization and resulting structures of organic-inorganic systems based on hybrid methacrylate oligomers have been Studied using SEC. DSC, and SAXS. The block and random oligomers with narrow polydipersity were prepared by group transfer polymerization. All the oligomers contain 3-(trimethoxysilyl)propyl methacrylates in the chain and form silsesquioxane (SSQO) Clusters by hydrolytic polycondensation, serving as cross-linking domains of the organic-inorganic network. The water miscibility and gelation of synthesized oligomers were evaluated. The Systems Studied can be divided into two groups-gelling and non-gelling oligomers as a result of the competition between cyclization and intermolecular reaction. The extent of cyclization and intermolecular polycondensation depend, on the oligomer structure. i.e. position and number of the functional trimethoxysilyl-monomer units, and on Molecular weight of the oligomeric chains. Due to the incompatibility of the SSQO framework and organic chains, microphase separation and structure ordering Occur during polymerization. (c) 2005 Elsevier Ltd. All rights reserved.