Sol-gel polymerization of organotrialkoxysilanes RSi(OR ')(3) and formation
of silsesquioxane (SSQO) structures was followed using SEC, Si-29 NMR, and
both small- and wide-angle X-ray scattering. Evolution of the SSQO structu
re is controlled by the competition between intermolecular polycondensation
and cyclization. A strong tendency to buildup of polyhedral cyclic oligome
rs-mainly octamer "cages" and larger cagelike structures-was found to grow
with increasing size of substituent R. As a result, long substituents preve
nt gelation of the trifunctional system and increase stability of the SSQO.
Because of incompatibility of the polyhedral SSQO framework and pendant or
ganic chains, microphase separation takes place and spontaneous self-organi
zation occurs. A micellar arrangement of compact SSQO domains with a correl
ation distance corresponding to the size of the substituent is formed, and
the ordering is promoted by increasing length of the organic chain. The mos
t organized arrangement was observed with the trialkoxysilanes substituted
with long PEO chains which crystallize and force the SSQO cages to align in
the lamellar structure.