Study On Synthesis And Properties Of Addition Liquid Fluorosilicone Rubber

Addition liquid fluorosilicone rubber is a liquid material for the addition reaction of silicon-vinyl in the basic polymer and silicon-hydrogen in the crosslinking agent.It was a kind of high-grade fluorosilicone rubber with the advantages of no by-product,low shrinkage,deep curing in vulcanization and excellent oil resistance.However,because of the early technology blockade abroad and the late start of domestic research,the research progress of addition liquid fluorosilicone rubber in our country has been restricted to a certain extent.In this paper,the synthesis and properties of fluorosilicone polymers and crosslinking agent of the addition liquid fluorosilicone rubber were studied.The preparation process of the addition liquid fluorosilicone rubber was put forward.The vulcanization characteristics,mechanical properties,low temperature properties,heat resistance and oil resistance of the addition liquid fluorosilicone rubber were discussed1-vinyl-3-hydroxy-1,1,3,3-tetramethyldisiloxane was first prepared,and the type and proportion of catalysts were determined.It was found that when FeCl3:AlCl3=1:3(mass ratio),the catalytic effect was the best.The optimum reaction temperature was 50-70?.The product obtained was characterized by infrared spectrum(IR)and nuclear magnetic resonance spectrum(1H-NMR),and the structure of end-capping agent was determined.Then,fluorosilicone polymers were prepared by bulk polymerization of trimethyltri(3,3,3-trifluoropropyl)cyclotrisiloxane(D3F)and the end-capping agent.The effects of reaction temperature and time on ring-opening polymerization of D3F were investigated.The optimum reaction temperature and time were determined to be 120-130? and 2-3h respectively.The relationship between viscosity and molecular weight of fluorosilicone polymers was studied by gel permeation chromatography(GPC).The fluorosilicone polymers were characterized by IR and 1H-NMR.Differential scanning calorimetry(DSC)was used to obtain the glass transition temperature of the fluorosilicone polymer at-69?,which was a non-crystalline.Thermogravimetric analysis(TGA)showed that the initial decomposition temperature of the fluorosilicone polymers increased from 355.9 C to 398.5 C with the increase of its viscosity,indicating that the thermal stability of fluorosilicone polymers increased with the increase of viscosity or molecular weight,and the degradation mechanism of fluorosilicone polymers was studied.The anhydrous aluminium trichloride was acidified with concentrated hydrochloric acid to enhance the catalytic activity of aluminium trichloride and effectively catalyzed the copolymerization of different monomers.The effects of reaction temperature and time on the copolymerization were verified.The optimum reaction temperature was 50-70 C and the reaction time was 4h.The structure of the crosslinking agent was characterized by IR and H-NMR.The thermo-oxidative stability of the crosslinking agent was studied by thermogravimetric analysis TGA.The results showed that the crosslinking agent was an ideal one for addition liquid fluorosilicone rubber.The vulcanization characteristics of addition liquid fluorosilicone rubber were studied by Rotorless vulcanization apparatus,and the optimum vulcanization temperature was determined to be 120 C.The effects of the viscosity of fluorosilicone polymers,the used amount and specific surface area of silica,the content of silicone hydroxyl group and hydrogen content of crosslinking agent on the mechanical properties of vulcanizates were studied.The effects of different fluorosilicone polymers were compared.In 1-vinyl-3-hydroxy-1,1,3,3-tetramethyl-disiloxane as the end-capping,there were two dimethylsiloxane uints separated between the vinyl groups at both ends of the molecular chain and the trifluoropropylmethylsiloxane uints in the molecular chain.This structure reduced the steric hindrance of trifluoropropyl group,compared with fluorosilicone polymers prepared by divinyltetramethyldisiloxane as end-capping agent.The cross-linking activity of the vinyl groups at both ends of the molecular chain was improved,and the addition reaction of vinyl-silicone and hydrogen-silicone better carried out during vulcanization,which improved the cross-linking effect and mechanical properties of the liquid fluorosilicone rubber.The results of TGA test showed that the initial decomposition temperature of addition liquid fluorosilicone rubber was about 380 C in oxygen atmosphere and about 455 C in nitrogen atmosphere.After post-cured,the mechanical properties of the rubber were basically the same as that of mold-cured,while the compression set was obviously improved.After the rubber was aged at 200 C for 24h,the hardness and resilience of the vulcanizate increased slightly,while the tensile strength and tear strength decreased slightly,it showed good heat resistance.The glass transition temperature of addition liquid fluorosilicone rubber was about-69 C,with good low temperature resistance.Because of side strong polar trifluoropropyl groups,its oil resistance was excellent.The volume change rate at 23? in fuel B was about 21%,in fuel C about 25%,and in IRM903 standard oil about 0.8%.That is,it was a good oil-resistant elastomer.