Mechanistic Insights into the Synthesis of Fully Condensed Polyhedral Octaphenylsilsesquioxane

A comprehensive study on the efficient one-pot synthesis of polyhedral octaphenylsilsesquioxane (OPS) is reported via the hydrolytic condensation of phenyltrimethoxysilane (PTMS) in the presence of basic catalyst to investigate the specific synthesis mechanism. The synthetic reactions are monitored with real time infrared (RTIR) spectroscopy. Then RTIR coupled with ²⁹Si nuclear magnetic resonance spectroscopy (NMR) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) are used to monitor the reactions and identify the intermediary species during the reaction. The rapid hydrolysis of PTMS is detected by RTIR. Contrary to previous reports, the ladder-like structured species are identified as intermediates during the reaction process. It is suggested that formation of caged T₈ OPS is realized through the chain break and rearrangement of the ladder-like phenyltrimethoxysilanes. Accordingly, a scheme from hydrolysis of the PTMS to formation of the OPS is provided.