Preparation And Property Of The High Performance Fluorosilicone Rubber

The development trends of rubber products are towards high performance,low power consumption and long life.General rubber such as natural rubber,chloroprene rubber,and acrylonitrile butadiene rubber has been difficult to meet the strict requirements for special rubber products in thermal stability,oil resistance and so on.Fluorosilicone rubber combines the advantages of fluororubber and silicone rubber,and thus exhibits excellent properties of high and low temperature resistance,solvent and oil resistance,and so on.It could be applied in many fields like astronavigation,automobile,machinery,electron,chemical industry and so on.However,there is still serious trouble in extending its application due to the high price and unsatisfactory synthesis technology.Furthermore,as it relates to the issue of commercial confidentiality,it is an important market rule for large foreign companies that only fluorosilicone mixed rubber should be available for sale rather than fluorosilicone raw rubber,let alone the transfer of technology.In china,fluorosilicone rubber is still in the beginning stages of development and there are still many technical problems.There is a wide gap between the foreign and domestic products in main performance,and thus it limits the application of domestic fluorosilicone rubber in many fields.Therefore,the research and development of high performance fluorosilicone rubber products are of great significance for China's fluorosilicone industrial technology.In this study,systematic studies are conducted aimed at the current main problems in fluorosilicone rubber field.Firstly,traditional balance methods were used to prepare hydroxy-terminated liquid fluorosilicone polymers,vinyl-terminated fluorosilicone copolymer and high molecular weight fluorosilicone polymer.The relationship between the molecular weight of the polymer and the capping agent dosage was studied.NMR spectra analysis showed that there is a deviation between the actual and theoretical value of the proportion of Me₂Si O chain unit.Fluorosilicone mixed rubber was prepared on this basis.The related formulation and preparation process were also studied.The mechanical properties,oil resistance,cold resistance and storage stability of fluorosilicone mixed rubber were tested to evaluate the influence of raw rubber with different fluorine content and viscosity.Secondly,in view of the serious deficiency in conventional polymerization process,a novel efficient method was employed to prepare highly pure fluorosilicone polymer.In conventional polymerization process,chain"back biting"reaction is inevitable and a cyclic product content as high as 80?90 wt%has been proved at equilibrium.This equilibrium makes the reaction process difficult to control and consequently,the molecular weight of fluorosilicone polymer is not stable enough,and molecular weight distribution is relatively broad.Furthermore,the initiator residue and high content of small molecule ring are also depressing problems,which seriously affect the product quality and the yield.Vacuum distillation proved to be not an efficient method and must increase production cost.In contrast,the new method,using ring-opening bulk polymerization reaction at lower temperatures by the addition of a reaction stabilizer,could obtain high-quality fluorosilicone and high isolated yield.The molecular weight can be controlled precisely by the regulation of the capping agent amount,with a polydispersity index of 1.4 or less and a?termination window?period of up to about 1 h.Via this method,the key problems in preparing fluorosilicone rubber could be solved.In addition,it has the advantage of simple equipment,easy operation,high safety,high yield and low cost,and thus it is a promising method for industrial application.Thirdly,the structure and viscoelastic properties of fumed silica gels in low molecular weight hydroxyl silicone oil were investigated by means of steady and dynamic rheology.It was noted that the fumed silica/hydroxyl silicone oil suspension exhibits shear-thickening under steady shear and?strain-thickening?under oscillatory shear condition.Effects of hydroxy groups on the rheological behavior of silicone oil suspension with highly dispersed hydrophilic amorphous silica were investigated by infrared,¹H-NMR and rheological test.The results show that the hydroxy groups on this system played an important role on the formation of shear thickening behavior of the suspension solution.At the same particle diameter and mass fraction,the amount of hydroxy groups on this system had a strong effect on increasing the viscosity of the suspension,which was likely due to multi-association hydrogen bonding between liquid molecules and silanol groups on fumed silica surfaces(Si-OH).Finally,poly(methyl(3,3,3-trifluoropropyl))siloxane(PMTFPS)was prepared by the anionic bulk ring-opening reaction of D₃F.D₃F has high activity for catalyzed anionic ring-opening reaction,using milder bases catalyst made of silicon alkoxide could obtain high molecular weight fluorosilicone.Vinyl groups were introduced to fluorosilicone by adding D₃^vi.Heat curable fluorosilicone rubber was prepared using different brands of silica including A380,HL200,LP and H20 as reinforcing fillers to evaluate the mechanical property and thermostability.With the addition of constitution controller such as hydroxyl fluorosilicone oil and diphenylsilanediol,the storability of the fluorosilicone rubber could be enhanced.