Polymerization of trialkoxysilanes. Effect of the organic substituent on the formation of gels (original) (raw)
Journal of Organometallic Chemistry, 2003
Organotrialkoxysilanes containing secondary hydroxyl groups were synthesized by reacting 1 mole of (3-aminopropyl)triethoxysilane (APS) with 1 or 2 mole of phenylglycidylether (PGE). Resulting products, APS–PGE and APS–PGE2, respectively, were subjected to hydrolytic condensation at 50 °C during 24 h. For APS–PGE, the reaction was performed using a molar ratio [H2O]/Si=3, without addition of an external catalyst. For APS–PGE2, the reaction was catalyzed by HCOOH or NaOH. Resulting poly(silsesquioxanes) (PSSO) were characterized by size exclusion chromatography, Fourier-transformed infrared spectroscopy and matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS). PSSO derived from APS–PGE and APS–PGE2, catalyzed by HCOOH, exhibited a relatively narrow distribution of polyhedral structures. This constitutes a simple one-step synthesis of polyhedral oligomeric silsesquioxanes (POSS) functionalized with amine and/or hydroxyl groups. The directionality of the reaction pathway towards the formation of polyhedral structures was ascribed to the formation of intramolecular SiOC bonds through the reaction of SiOEt or SiOH groups with secondary hydroxyl groups. Intramolecular SiOC bonds were found in the structures of APS–PGE and APS–PGE2, and in most of the species of the PSSO obtained from the NaOH-catalyzed reaction of APS–PGE2. A small fraction of surviving SiOC bonds was also found in the polyhedral structures of the PSSO derived from the hydrolytic condensation of APS–PGE and APS–PGE2 catalyzed by formic acid. By usual organic reactions transforming hydroxyl groups into other functional groups, it is possible to generate narrow distribution of multi-functionalized POSS starting from an OH-functionalized organotrialkoxysilane.The hydrolytic condensation of organotrialkoxysilanes containing secondary hydroxyl groups led to a narrow distribution of OH-functionalized polyhedral oligomeric silsesquioxanes. The generation of closed structures was ascribed to the reversible formation of intramolecular cycles through SiOC bonds. Under appropriate conditions, structures containing these cycles were present in high concentrations.