Synthesis, Processing And Properties Of Copolymerized Fluorosilicone Rubber

Fluorosilicone rubber combines the advantages of fluoro-rubber and silicone rubber, and exhibits the excellent properties of high and low temperature resistance, solvent and oil resistance, and so on. Fluorosilicone rubber can be applied in the important fields like astronavigation, automobile, electron and so on. Introducing of the dimethylsiloxane units into the main chain of fluorosilicone rubber would slightly affect the properties of material, while reduce the cost effectively. In this thesis, the fluorosilicone crude rubbers were synthetized by anionic bulk ring-opening copolymerization of y-(trifluoropropylmethyl)cyclotrisiloxane (D3F) and hexamethyl cyclotrisiloxane (D3), the reaction conditions were optimized and the reaction was scaled-up. The removal of the cyclic oligomers in the crude rubbers, reinforcing and vulcanization of the rubbers were also investigated, and the influences of several factors, such as cyclic oligomer content, the structure and usage of nanometer silica, the usages of the constitution controller and the vulcanizator, and the storage time, on the structure and properties of vulcanized rubber were obtained.Firstly, D3F/D3anionic bulk ring-opening copolymerizations were carried out using the initiator and a promoter. The variations of the molecular weight of the crude rubber and the mass percentage of cyclic oligomers were analyzed by GPC method. It was found that in the later stage of reaction, the molecular weight of the crude rubber was increased and then gradually decreased into an equilibrium value, the content of cyclic oligomers was varied in a contrary trend to the molecule weight. As the concentration of catalyst increased, the time to achieve the equilibrium state was reduced and the molecular weight of the crude rubber was decreased. The copolymerization rate could also be increased by increasing the concentration of promoter and the temperature. Adding of the end caping agent could decrease the molecular weight of the crude rubber. The optimized copolymerization conditions are obtained as follows:the concentration of initiator20ppm, the concentration of promoter2000ppm, polymerization temperature80℃and polymerization time75min.Secondly, the ring-opening copolymerization of D3F/D3was scaled-up using a self-cleaning kneader reactor. The crude rubbers prepared from the kneader reactor exhibited greater molecular weights, narrower molecular weight distribution and higher content of cyclic oligomers than the crude rubber prepared in the small reactor. The removal of the cyclic oligomers from the crude rubber was investigated using the drum wind drying oven, the vacuum drying oven and the self-cleaning reactor. The rate of devolatilization was fast at125℃using the drum wind drying method,70%of the cyclic oligomers could be removed in4h, and slight degradation was occurred at this condition. The molecule weight of cyclic oligomer increased quickly during devolatilization, which illustrated that the smaller cyclic volatilized firstly, and the main remaining cyclic oligomers exhibited greater molecular weight (i.e.D6F). The crude rubber was easily degraded in vacuum environment at temperature of>90℃, and the rate of devolatilization was slow below90℃. Using of the kneader reactor can update the surface of the reaction system all the time, which would favor to devolatilization of this high-viscosity system. By applying of two-step devolatilization method including the first devolatilization in vacuum at90℃for4h, and the second stripping by N2at125℃for4h, the crude rubber with cyclic oligomer content less than5%was obtained.Finally, the reinforcement of fluorosilicone rubber by nanometer silica, and the structure/property relationship of vulcanized rubber were studied. It was found that the structure and usage of nanometer silica, the mass ratio between silica and constitution controller had great influence on the dispersion of silica in rubber matrix and the properties of vulcanized rubber. The nanometer silica with greater specific surface area and homogeneous porosity dispersed well in the rubber matrix and exhibited a better reinforcement effect to rubber. Adding of the constitution controller would improve the compatibility between the rubber and silica, and the dispersion of silica was good when the mass ratio between silica and the constitution controller was7/1. As the concentration of silica increased, the hardness of vulcanized rubber was increased consequently, the degree of crosslinking and tensile strength were increased at first and then decreased. The rubber with lower cyclic oligomer content exhibited better mechanical properties. As the concentration of vulcanizator increased, the degree of crosslinking was increased. As the preservation prolonged, the structural effect was occurred, and the processability of the rubber become worse. Adding of0.9part of the vulcanizator,40part of silica and5.7part of the constitution controller to100part crude rubber, blending them in a torque rheometer, vulcanizing the rubber after1to3d storage, the vulcanized rubber exhibited the best comprehensive properties would be obtained.