| Liquid fluoroether rubber is a main chain and side chain carbon atoms on the part of the hydrogen atoms are replaced by fluorine atoms and side chains containing ether bond low molecular weight copolymer. The traditional solid fluoroether rubber is difficult to process, the use of limited form and other shortcomings, and liquid fluoroether rubber at room temperature with a certain degree of mobility, and molecular chain at both ends of the active group, so there are a variety of curing methods. As the liquid fluoroether rubber has excellent cold resistance, heat resistance, oil resistance, oxidation resistance and processing performance, from the car, aircraft and other fuel tank sealing to the electronic device bonding protection and other fields are widely used, so the study of liquid fluoroether rubber Preparation, end-modification and curing properties of great significance.In this paper, a high molecular weight vinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer was used as raw material to prepare end-carboxyl liquid fluoroether rubber (FM-COOH)by one-step oxidation degradation method. The product is white or light yellow liquid, 50? under the mobility is better. The reaction mechanism is:vinylidene fluoride - tetrafluoroethylene - perfluoromethyl vinyl ether terpolymer in the role of alkali elimination of HF to form C = C double bond,and then C = C double bond in the role of oxidant to form carboxyl The The carboxy-based fluoroether rubber has a carboxyl content of 0.35 to 2.67% and a number average molecular weight of 2100 to 13,000. The high molecular weight solid fluoroether rubber is dissolved in acetone / petroleum ether mixed solvent, and the method of dropping with alkali and oxidizing agent is beneficial to the preparation of liquid fluoroether rubber with low molecular weight and high carboxyl content. The reaction process to release a lot of heat,need to be carried out in the ice bath. The amount of alkali and oxidant is the main factor affecting the molecular weight and carboxyl content of liquid fluoroether rubber. When the molar ratio of H2O2 to KOH is 1.5, the product has the best performance.The use of polycarbodiimide as a curing agent, can be at room temperature to get the end of the liquid liquid fluoroether rubber curing products. The Tg of the cured product is -33.26 0 C, which is no significant change compared to the solid fluoroether rubber raw rubber, which is about 30 0 C lower than the Tg of the cured product of the conventional carboxyl liquid fluoroelastomer. It can be seen that the terminal carboxyl liquid fluoroether rubber has excellent low temperature performance The The tensile strength is 5?7MPa, the elongation at break is 150?190%, while the tensile strength of the cured product of the general side carboxyl liquid fluororubber is 3?5.5MPa, breaking elongation of 70?120%. Due to the introduction of the ether bond, liquid fluoroether rubber curing products, heat resistance and resistance to media properties than ordinary liquid fluorine rubber curing products slightly worse.The F2461-OH and FM-OH were synthesized by the esterification reaction of F2461-COOH and FM-COOH as raw materials. The carboxyl conversion of the obtained hydroxy liquid fluororubber was increased from 41.8% to 76.8% by studying the effect of the solvent type, the kind and amount of the catalyst, the temperature, the reaction time and the molar ratio of 1,4-butanediol to carboxyl groups on the carboxyl conversion, A hydroxyl content of 0.36% to 0.62%, and a number average molecular weight of 3,000 to 12,000.F2461-OHandFM-OH were used as dihydric alcohols in the laboratory to prepare fluorinated polyurethane prepolymer with TDI. The reaction conditions were as follows: ethyl acetate was used as solvent and dibutyltin dilaurate as catalyst, and reacted at 77? for 4 h. |
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