Synthesis and Characterization of a New (Tetrasilanol) Cyclosiloxane.

摘要

There has been recent interest in using incompletely condensed silsesquioxanes as molecular building blocks in many polymer systems. This interest is driven by significant property enhancements imparted by inclusion of a nanosized inorganic particulate into an organic matrix. Most of the work to date has focused on thermoplastic hybrid inorganic/organic copolymers derived from either a triol- or a diol-silsesquioxane (Figure 1). There is a need for the development of other incompletely condensed silsesquioxanes useful in both thermoplastics and thermosets. The authors have been studying the isolation and chemistry of a new cyclosiloxane containing four silanol functionalities. This tetrasilanol is tentatively assigned the structure shown in Figure 2, which is analogous to the known phenyl(2) and isopropyl(3) derivatives. Results of this experiment show that the hydrolytic condensation of cyclopentyltrichlorosilane in refluxing 80% acetone and water produces a high yield of the trisilanol shown in Figure 1, a small amount of a fully condensed octamer, along with some resinous polymer. A change in the solvent composition can result in significant changes to the product distribution. An attempt to produce a tetrasilanoldisiloxane, (C5H9) Si(OH)22O analogous to a cyclohexyl derivative reported by Brown using about 10% acetone and 90% water yielded a mixture of resinous products. However, the authors found that if the reaction was allowed to proceed for a longer time, a single major product, 1, was produced along with smaller amounts of other partially condensed silsesquioxanes. This major product can be isolated in about 50% yield. NMR spectroscopy reveals it to be a high symmetry compound containing a single silanol group per silicon. The three reasonable structures that fit all the available data are shown in Figure 3. Thus, a new completely condensed silsesquioxane tetraol has been synthesized and characterized. (3 figures, 5 refs.).