Preparation Of Siloxane-Oxyalkylene Copolymers And Their Application In Defoamers

In the past several years, siloxane-oxyalkylene copolymers are much researched. By graft reaction, hydrophilic polyoxyalkylene make the copolymer soluble, and hydrophobic polysiloxane make the copolymer low surface tension. So, the copolymers can be widely used in cosmetic, additive for textile, and defoamer.In this thesis, polyhydrosiloxanes is synthesized with octamethylcyclotetra-siloxane(D4) and high hydrogen-containing polyhydrosiloxanes as materials. In the presence of allyl alcohol as initiator and sodium hydroxide as catalyst, the polyoxyalkylene is synthesized. Then the graft reaction is made. The mol ratio of reactants, the catalyst concentration and the temperature were examined. The optimal experiment condition is as the following: the water content of the reactants mustbelow 0.05%, the mol ratio of CH2=CHCH2O-- and Si - H is 1.20:1,hexachloroplatinic acid is the catalyst and the weight concentration of Pt is 20 ~ 30ppm, the optimal reaction temperature is 100~ 110 for 4.0~4.5h.This thesis also introduces the use of siloxane-oxyalkylene copolymers in the defoamer. The optimal ratio of the components is acquired: siloxane-oxyalkylene copolymers 20.0%, fumed silica 3.0%, the multiple emulsifying agents (S-60, T-60) 2.5-3.0%, PEG6000 distearate 0.7~1.0%, water remainder. The defoamer is stable, and the defoaming effect is excellent. It can quickly dissolve in the water, and can be used not only solely but also together with other additives. When it is used, the emulsion breaking and the "oil-floating" will not happen, and no deposit appears. Besides, it is also effective to nonaqueous system. It has low surface tension, can quickly defoam, and the dosage is little. So the foreground of this defoamer's application is bright.