Abstract
2,4,6-Trimethyl-2,4,6-triphenylcyclotrisiloxane (P3) exists as cis and trans-stereoisomers. Herein, we present the detailed synthesis and characterization of the cis- and trans-P3 isomers. After preparation of the mixed cyclic methylphenylsiloxanes, it was found that vacuum distillation was the best method for separating P3 from the mixture of P3 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenylcyclotetrasiloxane (P4) on a large scale and that pure cis-P3 can be isolated by washing the mixed P3 isomers with methanol. It is also shown that a selective crystallization method was successful for isolating cis-P3 from the mixture of P3 and P4 directly and that large crystals may be obtained. Using gas chromatography and nuclear magnetic resonance (NMR) spectroscopy, the two different isomers and four different isomers in P3 and P4, respectively, are easily identified. The nuclear magnetic resonance (NMR) spectra, differential scanning calorimeter (DSC) thermograms, and infrared (IR) spectra with various ratios of cis-P3 and trans-P3 were also analyzed. A melting point depression of the cis-P3 was observed with an increased amount of trans-P3 for the mixed isomers, as expected. These P3 stereochemical isomers provide valuable starting materials for the preparation of stereoregular siloxanes using ring-opening polymerization.
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