Study Of Cyclosiloxane In-situ Copolymerization Crosslinking Systems And Their Application

Silicone rubber is prepared by ring-opening polymerization of circular siloxane to prepare linear polysiloxane,and then through vulcanization cross-linking to form siliconeelastomer.According to the form at room temperature,silicone rubber is usually divided into solid silicone rubber and liquid silicone rubber.Common silicone rubber,including liquid silicone rubber,has a large molecular weight,and the curing system has high viscosity and slow curing speed.These problems limit the application of silicone elastomer in 3D printing,nanoimprinting,narrow space encapsulation and other fields.Therefore,it has become a research hotspot to explore new synthesis methods and new curing technology of silicone rubber to make it suitable for rapid processing.Due to silicone rubber has excellent performance and function,its application in the 3D printing,nano-imprinting is more and more attention.Affected by the viscosity of silicone rubber and the way of cross-linking,related studies have focused on adding modifier change the thixotropy of silicone rubber precursor,or mixing silicone rubber with light-cured resin and curing in stages,and so on.None of these methods can fully meet the requirements of the application.Therefore,it is of great practical significance to develop a new synthesis and cross-linking system of silicone rubber,especially a reaction system with low viscosity and fast curing speed.Based on the above background,this paper designed and constructed a low viscosity,fast curing silicone rubber synthesis and cross-linking system.The design idea of this paper is to first synthesize a compound containing two siloxane rings,and then carry out in situ ringopening copolymerization with the cyclosiloxane monomer.The compound not only participates in the ring-opening reaction as the reaction monomer,but also acts as a crosslinking agent to make the polymer system cross-linked,so as to realize the rapid curing of the system from the low viscosity cyclosiloxane monomer to silicone rubber.Specifically,the following research work has been carried out:First,a low molecular weight polymer containing two siloxane rings was designed and synthesized.1,3-bis(tetramethyltriethylcyclotetrasiloxane)tetramethyldisiloxane(V4-MM-V4)was successfully prepared by the silohydroaddition reaction of D4Vi and MHMH.The purity of the product was 91.17%determined by liquid chromatography,and its molecular weight and structure were determined by MS,FTIR-ATR,1H-NMR and 13C-NMR.Secondly,organic silicone rubbers were prepared in situ with D4 and V4-MM-V4 as monomers by anionic ring-opening copolymerization and cationic ring-opening copolymerization.Compared with the two ring-opening systems,cationic ring-opening copolymerization system had a faster reaction speed and mild reaction conditions.Anionic ringopening copolymerization system could get higher molecular weight polymer,silicone rubber mechanical properties better.With the increase of V4-MM-V4 addition,the crosslinking density and specific gravity of the crosslinking chain increased,while the specific gravity of catenary and free chains decreased.The tensile strength of silicon rubber samples increased first and then decreased.The optimum tensile strength of anionic and cationic ring-opening silicone rubber samples were B30-0.5(2.11 MPa)and A30-1.5(1.44 MPa),respectively.The glass transition temperature domain of silicon rubber sample was widened and the crystallization melting peak disappeared,the low temperature performance was improved.The samples showed weight loss at 35℃-400℃,but the 10%weight loss temperature of the sample was near 500℃,showing good high temperature resistance.With the increase of filler addition,the polymer molecular weight of silicone rubber samples decreased gradually,and the proportion of free chain increased.When the amount of filler carbon black in anionic ring-opening copolymerization system was up to 30,the carbon black contacted with each other to form a complete path,and the thermal conductivity and electrical conductivity of the sample were rapidly improved.Finally,based on the characteristics of low initial viscosity and adjustable polymerization rate of cationic ring-opening copolymerization system,the application of in-situ copolymerization silicone rubber in nano-imprint lithography,electrical packaging and other fields was tested.The cyclosiloxane in situ copolymerization crosslinking system had very low initial viscosity,and by increasing the amount of catalyst and temperature,the reaction rate of the system could be accelerated to complete curing in 20S.The SEM test showed that the surface of silicon rubber sample obtained by R2P hot embossing has a clear micro/nano pattern.The water contact Angle of the sample increased by 25.4%compared with that of the blank sample.The air stability and light operation stability of perovskite solar cells encapsulated by in-situ copolymerized silicone rubber have been significantly improved.The in-situ copolymerized silicone rubber presents excellent sealing performance for battery devices.