Synthesis And Characterization Of Fluorosilicon Polymer With High Molecular Weight

Fluorosilicon rubber exhibits excellent properties of both silicon rubber and fluorine rubber, such as excellent low temeperature and high temperature-resistance, solvent and oil resistance. Thus, it is widely uesd in some important fields like astronavigation, auto, electron and so on. Fluorosilicone with high molecular weight is difficult to produce, and its systhesis technology is seldomly reported. It this thesis, l,3,5-tris(trifluoropropylmethyl)cyclotrisiloxane (FD₃) is polymerized by anion bulk polymerization to synthesize high molecule weight polymer, with emphsis on the influence of polymerization conditions on the conversion of FD3 to polymer and on the molecular weight of polymer formed. The strcture and propertis of the resulting fluorosilicone rubber measured and compared with the Russian product. Introducing of vinyl groups into fluorosilicon and its influence on the crosslinking behavior were also studied.FD₃ polymerization obeys the mechanism of anion ring-opening polymerization, and there exists a balance between high molecular weight product and cyclic products with lower molecular weigh. It was found the conversion increased first in the initial stage of polymerization, and levelled off or slightly decreased as polymerization proceeded for a longer time. The equilibrium conversion of polymer was greater than 95% when catalyst C was used in polymerization.Factors affecting the molecular weight of fluorosilicon polymer were investaiged in more detail. It was found that the purity of monomer, the existence of water or oxygen in the reaction system had significant influences on the molecule weight of product. In order to obtain fluorosilicon polymer with higher molecular weight, the purity of monomer should be greater than 99.5%, and the concentration of water and oxygen should be controlled very low. The fluorosilicone polymer prepared by using catalyst C had greater molecular weight than that of polymers prepared by using catalyst A or B. As the usage of catalyst C increased, the reaction rate was increased and the time to achieve equilibrium, and the molecule weight of polymer was decreased. Thepolymerization rate could also be increased by increasing the concentration of promoter and temperature, while the molecular weight of polymer changed no more. Vinyl comonomer had no significant effect on molecule weight, and adding of neutralization agent can enhance the polymer stability. Base on the above results, the optimized polymerization condtions was obtained as follows: the concentration of catalyst C 250ppm, the concentration of promoter D lOOOppm, polymerization temperature 80°C, polymerization time 60⁸0min.The fluorosilicone polymers with high molecular weight and various vinyl group contents were prepared based on the above conditions. The viscosity average molecular weight of self-made products was greater than l.OxlO6 and the molecule weight distribution was between 1.4 and 1.5. IR and H NMR results showed that the self-made products had the same structure with Russion product and the vinyl groups had effectively introduced into the polymer chains.The fluorosilicon polymers with different vinyl contents were vulcanized by using of benzyl peroxide. It was found that the gel content increased, and the equilibrium swelling degree decreased as the content of vinyl groups in polymer increased, eviding the increase of crosslinking degree of polymer. The tension and thermogravimetic performance of fluorosilicone rubber were also tested. It was showed that the fluorosilicon rubber was soft and weak, and the tensile strength and elongation at break was low when no touging agent was added.The copolymerization of FD3 and D3 was studied at last. By using the optimized catalyst system for FD3 homopolymerization, FD3/D3 coplymer can be ontained, but the molecaulr wight of copolymerization was lower than that of homopolymer.