Study On The Design,synthesis And Vulcanization Properties Of A New Type Of Fluorosilicone Polymer

Fluorosilicone polymer is a special silicone polymer with trifluoropropyl group on its side group.As a flexible fluorosilicone polymer,fluorosilicone rubber has an excellent service temperature range(-68-2320C)and both non-polar solvent and oil resistance due to its special structure,it is regarded as a new generation of aircraft integral fuel tank sealing material.Polymethyltrifluoropropyl siloxane is currently most commonly used type of fluorosilicone rubber.Because the trifluoropropyl side groups have a great shielding effect on the reactive end groups,this largely inhibits the room temperature reactivity of the fluorosilicone rubber.By introducing non-fluorine monomer units through copolymerization,copolymerized fluorosilicone rubber can be prepared,which can reduce the content of trifluoropropyl side groups,thereby reducing the shielding effect of trifluoropropyl and improving the room temperature vulcanization reaction activity,while the decrease of fluoropropyl content will also lead to the decrease of oil resistance.Therefore,the design and synthesis of a new type of fluorosilicone polymer with high trifluoropropyl content and high room temperature reactivity is necessary for the application of fluorosilicone rubber in the field of aircraft integral fuel tank sealing.In this paper,through the dehydrogenation condensation end-capping reaction of silanol and hydrosilyl,the alkoxy-terminated liquid fluorosilicone rubber with 100%trifluoropropyl unit content was designed and synthesized,including trimethoxy-terminated polymers(Ml,M2,M3 and M4),methyldimethoxy-terminated polymer(M5)and triethoxyterminated polymer(E1).The molecular structure of the product was confirmed by FTIR,1H NMR and 13C NMR.The evaluation method of room temperature vulcanization characteristics of alkoxy-terminated liquid fluorosilicone rubber was constructed by studying the relationship between dynamic viscosity and time and gel point time.The results show that the trimethoxy-terminated polymer can significantly improve the room temperature vulcanization reaction activity;the low molecular weight trimethoxy-terminated liquid fluorosilicone rubber(M1)has good compatibility with the base rubber when used as a crosslinking agent,which has a promoting effect on the dealcoholization vulcanization reaction.The effect is best when the amount of M1 is 4 phr;The larger the molecular weight of fluorosilicone rubber,the faster the dynamic viscosity increases and the shorter the gel time.Using synthetic trimethoxy-terminated liquid fluorosilicone rubber M2,M3 and M4 as the base rubber and M1 as the crosslinking agent,three two-component room temperature dealcoholization vulcanized sealants RTV-M2,RTV-M3 and RTV-M3 were prepared,which can be vulcanized quickly at room temperature.The mechanical properties,heat resistance and aging resistance of the sealant were studied after vulcanization.The results showed that the tensile strength was 3.0 MPa,the elongation at break was 105%,and the T5d in a nitrogen atmosphere was 430?,showing excellent comprehensive properties such as mechanics,heat resistance and aging resistance.