Study On Synthesis And Breaking & Inhibiting Foam Performance Of Polysiloxanes Modified With Fluoroalkyl Groups

Polysiloxanes modified with fluoroalkyl were widely used in vehicle, rubber, astronavigation, petrochemical processing, ink, coating, and so on. Because of low surface tension, water-repellent and oil-repellent performance of polysiloxanes modified with fluoroalkyl, which are two basic conditions for substance used for defoamer, therefore product can be used as defoamer in oil-based system.Here, synthesis and breaking and inhibiting foam performance of polysiloxanes modified with different fluoroalkyls in mixture of diesel and mobile fuel processes of different were discussed. And the possible antifoaming mechanism and problem of performance exhaust of modified polysiloxanes with the change of time were analyzed, which provide reference for choosing suitable defoamer in special oil-based systems.Synthesis of polysiloxanes modified with 3,3,3-trifluoropropyl groups or a series of acrylates containing fluoroine atoms (ACFA) was studied, and effects of content of fluoroalkyl on breaking and inhibiting foam performance of modified products were discussed. Results show that breaking foam performance of polytri-fluoropropylmethylsiloxane (PTFMS) is not changing with the increase of the molar content of trifluoropropy (x(D~F)) , but foam inhibiting performance of PTFMS becomes better. And hydrophobic silica cannot improve breaking and inhibiting foam performance of PTFMS in studied oil-based system. When polysiloxanes being modified with a series of ACFA with different carbon atom number, with the increase of carbon number in ACFA, surface tension of modified products is outstanding decreasing, and breaking and inhibiting foam performance becomes extraordinarily better. Breaking and inhibiting foam performance of polysiloxanes modified with fluoroalkyls is related with dispersion performance and surface tension of modified products. It is possible that breaking foam process of polysiloxanes modified with fluoroalkyl follows "Bridging-Spreading" mechanism. Effects of hydrophobic degree of silica on breaking and inhibiting foam performance of antifoam active composition (AAC), which prepared with PTFMS and silica, were studied in aqueous solution of 0.5%PVA by weight or 0.5%LAS by weight. And results show that the low hydrophobic degree is helpful for breaking foam performance of AAC in aqueous solution of 0.5%PVA; the high hydrophobic degree is benefitful for breaking foam performance of AAC in aqueous solution of 0.5%LAS.Because of the high price of fluoroalkyl, polysiloxanes modified with both polyethers and fluoroalkyls were synthesized, and the breaking and inhibiting foam performance of modified products in mixture of diesel and mobile fuel were also studied. Results show that with the increase of viscosity of polysiloxanes, breaking foam performance of polysiloxanes modified with same polyether and 3,3,3-trifluoropropyl groups becomes worse, but inhibiting foam performance becomes better. With the increase of molecular weight of polyether cannot improve breaking foam speed, and inhibiting foam performance changes for better, but not obviously. Polysiloxanes modified with allyl polyoxypropylene ether and ACFA of the molar ratio between them being 3:7 can combine two kinds of foam control properties of polysiloxane modified with allyl polyoxypropylene ether and polysiloxane modified with fluoroalkyl, alone. With the increase of length of fluoroalkyl chain, surface tension of polysiloxane modified with polyether and fluoroalkyl goes down, and both of the breaking foam performance and inhibiting foam performance become better. Exhaust of antifoaming performance of modified products is related with particle size of modified product become bigger during the course of test, also related with the change of surface tension of foaming medium before and after the breaking foam performance test.