The Preparation Of High-Viscosity Silicone Oil By Depolymerized Siloxanes

This study works on how to prepare high viscosity sillcone oil with siloxane mixtures that come from degradation of waste silicone. Acid catalyst is normally used to depolymerize silicone materials, so the crude mixture DMC is acidity and deep colour. It contains inhibitor, and the amount of octamethylcyclotetrasiloxane (D4) in siloxane mixtures is less. High-viscosity silicone oil isn't got by the polymerization of crude DMC. So as to deal with above problems, different processes were taken.1. Crude DMC was neutralized by alkali, but the yield of silicone oil was only 20.09%, the highest viscosity was 450 MPa·s, and the colour was yellow.2. The rearrangement process was consided. It consisted of polymerization of crude DMC, high-temperature depolymerization and distillation new DMC. Inhibitor and acid were reduced and D4 was increased after rearrangment. High-viscosity and narrow distribution of molecular weight was attained.Rearrangement processwas done in acid and alkali catalyst.The yield of acid rearrangement product was little. The colour of DMC was light yellow and it was easy to self-polymerization. On the other hand the yield of alkali rearrangement was high, and the colour of product was fair.The following influencing factors were considered for alkali rearrangement process of raw siloxanes. The catalyst of rearrangement was potassium hydroxide, The ratio of catalyst to raw material was 2.5‰, 300mmHg was choosed as the polymerization vacuum and 600mmHg as the depolymerization vacuum, the distillation was carried out in two temperature stages, the temperature was heated to 190 in 1.5 hours, and stay for a while at 190-200℃, rearrangement yield was 69%, then heated to about 235℃.The polymerization catalyst of rearrangement product was tetramethylammonium hydroxide, the ratio of catalyst to raw material was 0.48‰, and the polymerization temperature was 110±2℃. High viscosity silicone oil could be prepared and the color was fair by rearrangement process. Its viscosity could reach 100000 MPa·s. It was measured that the weight -average molecular weight of silicone oil was 162190 by rearrangement of crude DMC, 202999 prepared by pure DMC, and 29127 by merchandise DMC.We selected rearrangement process to prepare silicone oil in the end .