Synthesis And Cure Of Active-Terminated Liquid Fluoroelastomer

Liquid fluoroelastomer with low molecular weight exhibits excellent fuel resistance, thermal oxidative stability and processability. It is suitable for sealing the fuel tanks of aircraft and coating the external surfaces of building owing to overcoming the practical limitations in size and shape of high molecular weight fluoroelastomer which is mostly formed by compression molding. Carboxyl-terminated liquid fluoroelastomers with low molecular weight have been prepared by our laboratory. For the low molecular weight polymer, the terminal groups can significantly affect its performance, in particular thermal stability and curing properties.At high temperatures the carboxyl group of carboxyl-terminated liquid fluoroelastomer will be degradated, thus the life of the product will be affected. Therefore, the modification of the terminal carboxyl end groups is important.In this paper, hydroxyl-terminated liquid fluoroelastomers is prepared by reduction reaction of carboxyl-terminated liquid fluoroelastomers. NMR and FTIR are adopted to characterize the structure of synthetic product. Hydroxyl-terminated liquid fluoroelastomers with number molecular weight (Mn) ranged from 3000 to 10100 and hydroxyl content ranged from 1.0wt% to 2.30wt%,were prepared. Product is a light yellow transparent liquid and has good flowability at 60℃. By controlling the reaction conditions, product with the conversion rate of 89% to 100% can be obtained. In this reaction, the amount of reducing agent, the molecular structure and molecular weight of the material and the reaction time, reaction temperature, reaction pressure, and the order of addition of factors can also influence product properties.In this paper, the conversion rate is effectively improved by discussion of the above factors.The curing properties of the synthesized hydroxyl-terminated liquid fluoroelastomers were studied. Effective curing system and curing conditions have been determined by the study on the factors such as the addition amount of the isocyanate, curing temperature, curing accelerator. The properties of the cured products were tested and the results showed that although the molecular weight of the hydroxyl-terminated liquid fluoroelastomers is much lower than the average solid fluoroelastomer, but its cured product still has excellent heat stability and chemical resistance, however, its mechanical properties are slightly lower than the solid fluoroelastomer.In this paper, a exploratory modification of the hydroxyl end group has been studied. Liquid fluoroelastomers with different end groups have been prepared,which used Mitsunobu reaction to convert the terminal hydroxyl group to the amino and aryl sulfonic acid groups. The product can improve the insufficient of fluoroelastomers and can broaden its curing methods.