Synthesis Of Hydroxy-Terminated Fluorocarbon Oligomers And Preparation And Properties Of Fluorinated Polyurethanes

Fluorinated polyurethane is a special polyurethane material containing fluorine element.In addition to excellent mechanical properties of polyurethane,fluorine atom gives the material special surface characteristics.It is often used as protective coating,sealing parts and other products in the fields of national defense,aerospace and petrochemical industry.One of the research directions in this field is to explore new fluorine-containing compounds for the preparation of fluorinated polyurethane and to improve the structural designability of it.In this paper,poly(vinylidene fluoride-hexafluoropropylene)copolymerwaschangedinto hydroxy-terminated fluorocarbon oligomer by oxidative degradation and functional group conversion,and the hydroxy-terminated oligomer was reacted with isocyanate to prepare fluorinated polyurethane.By adjusting the proportion of hydroxy-terminated fluorocarbon oligomers and polyether polyols to change the content of fluorine elements in the material,the influence of the addition amount of fluorine-containing chain segments on the material properties was studied.The specific work was as follows:(1)Carboxy-terminated fluorocarbon oligomers were prepared from poly(vinylidene fluoride-hexafluoropropylene)copolymer by oxidative degradation.Inalkalineenvironment,poly(vinylidene fluoride-hexafluoropropylene)copolymerwasdegradedinto carboxy-terminated fluorocarbon oligomers by hydrogen peroxide with molecular weight below 10000.The effects of oxidation conditions on molecular weight and functional properties of the product were studied.The one-step feeding method of adding hydrogen peroxide first and then potassium hydroxide is beneficial to the degradation reaction.The effect is better in the temperature range of 10-20~oC.The molecular weight of the product decreases first and then increases when the amount of alkali and oxidant is increased.(2)Hydroxy-terminated fluorocarbon oligomers were synthesized from carboxy-terminated fluorocarbon oligomers by sodium borohydride/sulfuric acid complex reduction system.The effects of reaction conditions on carboxy-terminated conversion rate were studied.When the molar ratio of sodium borohydride and sulfuric acid to carboxyl group in reactants is 2.5:2:1,and the refluxing temperature is in the range of 80-100~oC,the product conversion rate can reaches more than 80%.(3)Fluorinated polyurethanes were prepared by reacting the hydroxy-terminated fluorocarbon oligomers with polytetrahydrofuranediol,isophorone diisocyanate and trimethylol propane.Fluorinated polyurethanes with fluorine content of 21-40%were prepared by adjusting the proportion of fluorinated alcohol chain segments and polytetrahydrofuranediol chain segments.The effects of fluorine content on the microstructure,mechanical and thermal properties of polyurethane were studied.The results show that the mechanical properties of the material are better when the ratio of the two components is 1:3-1:5,and the introduction of the fluorine content can improve the tensile strength of the material.