Synthesis And Properties Of High Reactive Siloxane Modified Polyether

Sealant is a thermoplastic polymer elastomer with excellent adhesion,good elasticity,light weight,high strength and strong corrosion resistance.It is widely used in major engineering fields such as construction,automotive,machinery manufacturing,energy and electrical engineering.However,with people's growing awareness of environmental protection and safety,there are two major problems in the current sealant:there are two major problems in the current sealant:(1)to handle the inconvenience brought by the high viscosity of base material,a large amount of volatile organic solvent must be used as a diluent to reduce the viscosity which not only harms human health,but also destroys the atmospheric ozone layer;(2)in order to increase the curing reaction rate at room temperature,organotin compounds are usually used as catalysts to shorten the curing time of the rubber which will do harm to the environmentdue to its high toxicity.In view of the above problems,a low-viscosity,fast-curing highly reactive silane-terminated polyether is prepared by synthesizing a highly reactive silane and a modified polyether thereof to meet the use requirement of a high-performance sealant.In this dissertation,the reaction mechanism of the highly reactive isocyanate methyltriethoxysilane was studied using chloromethyltriethoxysilane as the monomer.The effect of reaction temperature,catalyst,and blocking agent on the yield was investigated to obtain stable and reliable High reactivity silane preparation process technical parameters.Further,based on the reaction mechanism of the highly reactive isocyanate methyltriethoxysilane,a novel silane-terminated polyether reaction model was constructed to solve the current scientific problem of high viscosity and slow curing speed of the sealant base material.The research of this topic is divided into three parts.The main contents are as follows:In the first part,chloromethyltriethoxysilane and potassium cyanate were used as raw materials,alcohols with different carbon chain lengths were used as blocking agents,and N,N-dimethylformamide was used as a solvent to synthesize high reactive silanes withthe carbamate structure.The reaction factors such as reaction temperature,feed molar ratio,dripping rate,catalyst and different carbon chain length,etc.,were studied to investigate the effect of reaction factors on the yield of highly reactive silanes,through nuclear magnetic resonance(NMR),infrared spectrometer(IR),and energy Spectrometer(EDS)and other test instruments to characterize the structure of the reaction products,and the reaction mechanism of highly reactive silanes with urethane structure was explored.In the second part,a series of high-activity silane-terminated polyethers were prepared by end-modification of 1000 averagemolecular weight polypropylene glycol with a high activity silane,changing the NCO/OH molar ratio to study its influence on the surface-drying time,rheological properties,thermal stability,transparency and hardness to determine the best process parameters.The results showed that when the NCO/OH molar ratio was 1.25,the prepared highly active silane-terminated polyether had excellent properties,such aslow viscosity,fast curing,and good transparency.In the third part,polypropylene glycol with different average molecular weight was selected as the research object,which was modified by high activity silane,and a series of high-activity silane-terminated polyethers were prepared by controlling the NCO/OH molar ratio to remain unchanged at 1.25.To investigate the effects of surface dry time,rheological properties,thermal stability,transparency,hardness,etc.,the influence mechanism of the average molecular weight of polypropylene glycol on the high activity of silane-terminated polyether was discussed.The results show that with the increase of the molecular weight of polypropylene glycol,the viscosity of the prepolymer increases,and the surface dry time first decreases and then increases,and the hardness of the cross-linked cured film decreases.When the number average molecular weight of polypropylene glycol is 1000,the surface dry time for preparing the highly active silane-terminated polyether is 2 h,the viscosity is 350 mPa-s,the gel time is 5.6 h,and the cured film is colorless and transparent,and the visible light is transparent.The rate is 91.9%and the hardness is 16A.The results showed that with the increase of the molecular weight of polypropylene glycol,the viscosity of the prepolymer increased,and the tack-free time showed a trend of shortening and then increasing,while the hardness of the cross-linked cured film decreased.When the average molecular weight of polypropylene glycol is yttrium,the preparation of highly active silane-terminated polyethers has a tack-free time of 2 h,a viscosity of 350 mPa-s,a gelling time of 5.6 h,and the cured film is colorless,transparent and visible,with a transmittance of 91.9%and the hardness of 16 A.In this dissertation,a highly reactive silane with carbamate structure and a series of highly reactive silane-terminated polyethers with different molecular weights had been successfully prepared.This solves the problem of high viscosity and slow curing of the sealant base material and can meet the needs of high-performance coatings,adhesives and sealants,which has broad application prospects.