The Study On Copolymerization Emulsion Of Polysiloxane And Acrylic Ester

In this paper, a kind of acrylic ester emulsion modified by siloxane is made and its principle of synthesis is studied. This kind of emulsion will be used as matrices for exterior wall paint of high performance. The process of the preparation of the kind of emulsion mainly includes two important parts.The first part is emulsion polymerization of polysiloxane , that is , octamethylcyclotetrasiloxane polymerizes into polysiloxane emulsion by means of ring-expansion under emulsion and acid conditions. Three kinds of vinyltrialkoxysilicone (WD-20, WD-21 and WD-70), which is added respectively to the emulsion before polymerization, can improve the compatibility between the polyacrylate and the polysiloxane .In addition , the choices of the emulsifiers system and the catalyst are discussed. A conclusion can be drawn that only the emulsifiers system is made from sodium dodecylbenzene sulfonate and OP-10, can the emulsion polymerization gain good polymerization stability. The total dosage of the emulsifiers should be limited from 3 percent to 4 percent ,and the ratio between sodium dodecylbenzene sulfonate and OP-10 should be limited from 2:1 to 1:1. Dodecylbenezene sulfonic acid is chosen as the catalyst in order to obtain good polymerization stability.The characteristics of each kind of WD ,including the relative velocity of the hydrolysis and polycondensation reaction and the ability of homopolymerization reaction are also demonsrated. It show that the order of the relative velocity is WD-21 >WD-70>WD-20,and that the polysiloxanepolymerization ,when added WD-21 or WD-70, can reach a faster polymerization speed and a higher solid content. So WD-21 is the best to be chosen, WD-70better ,WD-20never.The second part is the free radical emulsion polymerization ofacrylic ester. It use the polysiloxane emulsion above as the seed emulsion. In this part, several orthogonal tests are made, and through range analysis and order tendency analysis the effects of four factors on emulsion polymerization stability , bin stability ,film forming performance and paint film performance are discussed. The four main factors include the dosage of dodecylbenezene sulfonic acid, the dosage of alkoxylsiloxane, the dosage of acrylic acid and the ratio between methylmethacrylate and butyl acrylate monomer. So a kind of silicone-acrylic ester emulsion is made with proper polysiloxane content., good polymerization and storage stability, good film forming performance and good paint film performance. Besides all above, the modification mechanism of this kind of silicone-acrylic ester emulsion is testified perfectly by infrar-red spectrum analysis. The results of TEM and DSC are also show the microscopic dispersion structure of the polysiloxane in the polyacrylate. With the polysiloxane content increasing, the dispersion of polysiloxane in the polyacrylate varies from molecular lever to kernel state.