Synthesis Of Phosphorus-Fluoride Containing Polysiloxane Flame Retardants And Their Modified Epoxy Resins

Ehancing the flame retardant properties of epoxy resins has always been an important topic in the field of epoxy resin research.The current modification methods can enhance the flame retardant properties of epoxy resins at the expense of the excellent properties of epoxy resins,such as thermal stability,light transmittance and mechanical properties of epoxy resins.Therefore,how to enhance the flame retardant properties of EP on the basis of maintaining the excellent properties of EP itself has important application value and scientific significance.In order to solve this problem,two phosphorus-and fluorine-containing polysiloxane flame retardants were designed and synthesized in this paper,and their effects on the thermal stability,flame retardancy,mechanical properties and light transmittance of EP were systematically studied.The specific content is as follows:9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide,Vinyltriethoxysilane,γ-Aminopropyltriethoxysilane and Hexamethyldisiloxane were used as raw materials to synthesize the hyperbranched polysiloxane containing amino and DOPO groups（HPBSi-Ⅰ）,the structure of HPBSi-Ⅰwas characterized by FTIR,¹H NMR and ³¹P NMR.A series of flame retardant modified epoxy resins were prepared by adding HPBSi-Ⅰinto epoxy resins.The thermal stability,flame retardancy,mechanical properties and optical properties of epoxy resins were analyzed by TGA,DMA,UV-Vis,LOI,UL-94 and CONE;the flame retardant mechanism of HPBSi-Ⅰwas explored by TGA-MS and SEM-EDX.The test results showed that the modified epoxy resin had good optical properties,and the transmittance in the ultraviolet-visible region was more than 93%;The TGA test results showed that the HPBSi-Ⅰreduced the pyrolysis rate of epoxy resin,increased the carbon residue rate after pyrolysis of epoxy resin,and improved the thermal stability of the resin;The flame retardant test showed that when the content of HPBSi-I in the epoxy resin reached 3 wt%,the LOI value of the epoxy resin reached 31.4,and passed the UL-94 V-0 rating test,which made the modified epoxy resin show the excellent flame retardant performance.The flame retardant mechanism is that DOPO and siloxane can participate in carbon formation,forming a stable carbon layer containing silicon and phosphorus,which can hinder the further combustion of the resin;the phosphorus oxygen radicals generated by the pyrolysis of DOPO can quench the reactive free radicals of epoxy resin,which can interrupt the combustion reaction in the gas phase.Synthesis of polysiloxane（HPBSi-Ⅱ）containing DOPO,perfluorodecyl and epoxy groups by sol-gel method,and the epoxy resin composites were prepared by adding HPBSi-Ⅱinto epoxy resin.The test showed that HPBSi-Ⅱhad a good compatibility with epoxy resin,and the epoxy resin composites had good light transmittance;perfluorodecyl of HPBSi-Ⅱreduced the surface energy of the modified epoxy resin,when the content of HPBSi-II reached 7 wt%,the surface energy of the modified epoxy resin was reduced from 28.67 m N/m of pure epoxy resin to 13.43 m N/m,the water contact angle reached103°,and the hydrophobic and oleophobic properties of modified epoxy resin were significantly enhanced;HPBSi-Ⅱenhanced the flame retardant properties of epoxy resin,when the content of HPBSi-Ⅱin epoxy resin reached 3 wt%,the LOI value of the modified epoxy resin was increased to 30.2 and passed the UL-94 V-0 grade,the heat release rate of modified epoxy resin decreased significantly;the flame retardant mechanism is that the quenching effect of free radicals and the catalytic carbonization of DOPO,and siloxane can participate in the formation of the carbon layer and improve the stability of the carbon layer.In addition,HPBSi-Ⅱalso improved the elastic modulus of epoxy resin,which can enhance the ability of epoxy resin to resist deformation.