Study On The Balanced Synthesis And Devolatilization Of Hydroxyl-Terminated Polydimethylsiloxane And Reactor

At present, hydroxyl-terminated polydimethylsiloxane (PDMS) was generally synthesized with batch process in China, that is, hydroxyl-terminated PDMS was synthesized firstly, then water was put into it for degradation. The viscosity of the product was hard to control and the molecular weight distribution (MWD) of the products was wide, so the quality of the product was not so high. In this article, hydroxyl-terminated PDMS was synthesized and was studied in self-cleaning reactor, then, the devolatilization of hydroxyl terminated PDMS was studied in single-screw extruder. The residence time distribution (RTD) of the self-cleaning reactor was studied. Finally one pilot experimental scheme was proposed.The hydroxyl-terminated PDMS was balanced synthesized by ring-opening of Octamethylcyclotetrasiloxane (D4) in self-cleaning reactor, with potassium hydroxide (KOH) or tetramethyl ammonium hydroxide [(CH3)4NOH]] as the catalyst. The study focused on the efficiency of the two catalysts, and the amount of catalyst and reaction time on the conversion of the balanced reaction. It was found that the efficiency of [(CH3)4NOH]] was higher than that of KOH, and the reaction could be equilibrated at temperature 110 for 1.5 hours, and the loss ratio of the water that put into the reactor was almost equal to conversion of the reaction. So we can control the conversion of the reaction by controlling the condition of the reaction, then we can calculate the quantity of water we should put into the reactor.About the devolatilization of hydroxyl-terminated PDMS in a single-screw extruder, the factors that affect final mass fraction of the volatile were analyzed. It was found that both temperature and vacuum were the key parameters. Then the formulas between the final mass fraction of volatile with the rotational speed of the screw and with the feed rate were proposed respectively.In the study of self-cleaning reactor, water and syrup were adopted as the experimental media and the researches were focused on the characterization of the RTD. The residence time distributions were tested, and the relations between the backflow coefficient and rotational speed, viscosity, feed rate and the angle between two adjacent blades were studied, and the formulas between backflow coefficient and the mixing Reynolds were proposed. It was found that the experimental curves were in consist with the theoretical ones well.