Reduction Of Liquid Carboxylate Fluororubber By Sodium Borohydride/rare Earth Chloride System And Its Curing

As a kind of polymer with low molecular weight,liquid fluorine rubber has good fluidity and plasticity on the basis of excellent properties such as heat stability,solvent resistance and weather aging resistance of solid fluorine rubber.It consumes less energy in processing and molding and is more conducive to industrial production.Liquid fluorine rubber has been widely used in aerospace,automotive,petrochemical and medical fields.There are many studies on fluoro rubber in foreign countries,but the research on fluoro rubber in China is limited,and the research on liquid fluoro rubber is even less.Therefore,in this paper,liquid carboxyl-terminated fluoroprene rubber was prepared by oxidative degradation method and sodium borohydride(NaBH4)/rare earth chloride(RECl3)was used as the reduction system to prepare liquid hydroxy-terminated fluoroprene rubber through reduction reaction.Four rare earth chloride such as samarium chloride,lanthanum chloride,cerium chloride and neodymium chloride were selected.In addition,aziridine was used as a curing agent to cure liquid carboxyl-terminated fluorine rubber.The structure of the product was analyzed by means of infrared(FTIR)and nuclear magnetism(NMR).The results show that:With NaBH4-REC13 as the reduction system,the reduction rate increased with the increase of reaction temperature and reaction time in both type 26 and type 246 liquid carboxyl-terminated fluoroprene rubber.When the reaction temperature reaches 90? and the reaction time exceeds 6h,the reduction rate becomes stable.With the increase of the dosage of RoCOOH/NaBH4/REC13,the reduction rate increases first and then decreased.When the ratio is 1/4/2,the reduction rate reaches the optimal value,while when the ratio is 1/5/2.5,the reduction rate significantly decreases.Therefore,based on the above conditions,the optimal reaction conditions under the system of NaBH4/REC13 are as follows:reaction temperature is 90?,reaction time is 6h,ratio of RoCOOH/NaBH4/REC13 is 1/4/2.Among the four rare earth chloride,samarium chloride is the most effective,followed by neodymium chloride and cerium chloride,and finally lanthanum chloride.Aziridine can cure liquid carboxyl-terminated fluororubber successfully,and the cured products have good heat resistance,solvent resistance and mechanical properties.The curing process is mainly divided into two stages:230?245? and 390?420?.With the increase of curing time and aziridine dosage,the comprehensive performance of the product is gradually improved.When the curing time is 4h,the curing temperature is 100?,and the curing agent dosage is 14%,the comprehensive performance of the curing product is the best.