In this embodiment, trimethylsilyl chloride was included in the initial feed to the reactor to reduce the RSUA content in the product RSUTMS. Hexamethyldisiloxane (28.3 g, 0.174 mol) and trimethylchlorosilane (CTMS, 2.8 g, 0.0258 mol) were added to the C oscillation tube. After sealing the reaction tube, it was cooled in dry ice, evacuated and subsequently RSU (33 g, 0.183 mol) was added. The reaction tube was heated at 105°C for 6 hours to a maximum pressure of 67 psig (0.56 MPa) during the reaction. Upon completion of the reaction, the mixture was cooled to room temperature and the yellow-brown liquid product was transferred to a distillation flask. Analysis of the crude product by 1H NMR showed a conversion of about 93% based on the limiting reactant hexamethyldisiloxane.19F NMR analysis of the reaction mixture indicated that the concentration of RSUA relative to RSUTMS was about 8.6 mol%. The low-boiling components (RSU and fluorotrimethylsilane) were first removed by distillation at atmospheric pressure until the tank temperature reached 103 °C. The reaction was carried out at a pressure of 0.5 mmHg (4 mmHg). Subsequent distillation of RSUTMS at a pressure of 34 mmHg (4.5 kPa) yielded 34.6 g (0.138 mol) of product containing about 2 mole % of RSUA. the distillation product had a yield of 84% over a 6 hour reaction time. The lower RSUA content compared to Example 1 without added CTMS demonstrates the effectiveness of adding trimethylmethylsilyl chloride at the beginning of the reaction.
