Study on the mechanism of the formation of polyhedral oligomeric silsesquioxanes by the 2D correlation infrared spectral

Synthesis of polyhedral oligomeric silsesquioxanes (POSS) by the hydrolytic condensation reaction of trifunctional organosilanes [e.g., RSiCl3 or RSi(OR)3] may have achieved success. However, the exact formation mechanism of POSS, especially, an evolution process in the reaction still remains unclear. In this work, a real-time FTIR was carried out to trace the synthesis process of POSS. It was found that linear siloxanes, cyclic siloxanes, and cage-like polysiloxanes were formed during the reaction. With the help of generalized two-dimensional (2D) correlation analysis, we obtained exact sequential change among the three siolxanes, with the linear silicons formed initially. Following this was the emergence of cyclic siloxanes, and finally the cage-like polysiloxanes. Consequently, we not only proved the existence of the linear and cyclic siloxanes but also accurately detected the sequential change of the siloxanes in the process, which exhibited an intact and visual evolution process of POSS formation. Based on this, the reaction mechanism is presented. Finally, the chemical structure of cage-like products was further characterized by 29Si-NMR and GPC measurements. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012