Cage-ladder-struture, Phosphorus-containing POSS Reactive-type Flame Retardants And Their Application In Epoxy Resin

Epoxy resins have been widely used as matrices for fiber-reinforced composite materials,coatings,structural adhesives,and electronic packaging due to their excellent comprehensive properties.Flammability of epoxy resins restricts their application in the fields where high flame retardancy is required.In recent years,with the growing voice of global environmental protection,traditional halogen-containing flame-retardants will be gradually abandoned,flame retardant epoxy resins are facing new challenges.In this study,cage/ladder structure POSS,phosphorus-containing and reactive?epoxy,amine?substituents are introduced to the flame retardants to yield novel flame retardant epoxy resin systems.Influences of the functional substituents on the thermal,mechanical and flame retardant properties of the epoxy resin materials are systematically investigated.The main research contents are listed as follows:1.A novel cage/ladder structure phosphorus-containing polyhedral oligomeric silsesquinoxanes?CLEP-DOPO-POSS?was successfully synthesized via the hydrolytic condensationof9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane?DOPO-VTMS?with?3,4-epoxycyclohexyl?ethyltrimethoxysilane?KH530?,and then incorporated into epoxy resins?EPs?in different ratios using thermal curing technology.The structure of CLEP-DOPO-POSS was confirmed by Fourier transform infrared spectroscopy?FTIR?,NMR spectroscopy(¹HNMR and ²⁹Si-NMR),MALDI-TOF and XRD.Thermal stability,mechanical properties and flame retardancy effect of CLEP-DOPO-POSS on epoxy resin were comprehensively evaluated via TGA,DMA,universal tensile testing,LOI,UL-94,and cone calorimetry.The flame-retardant mechanism of the EP modified with CLEP-DOPO-POSS was investigated by TGA-IR,TGA-MS,and scanning electron microscopy.Experimental results showed that CLEP-DOPO-POSS was homogeneously dispersed in the EP matrix.The LOI value can reach up to 31.9%and UL-94V-0 standard test has been achieved by the presence of only 2.91 wt%CLEP-DOPO-POSS.In addition,the EP composite containing CLEP-DOPO-POSS exhibited better thermal stability and mechanical properties.The flame-retardant mechanism was attributed to the quenching effect of phosphorus-containing free radicals and the formation of phosphorus and silicon containing char layers in the condensed phase.2.To further expand the application scope of this kind of flame retardant,a novel cage/ladderstructureamino-containingpolyhedraloligomericsilsesquinoxanes?CLNH₂-DOPO-POSS?was successfully synthesized via the hydrolytic condensation of9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane?DOPO-VTMS?with aminopropyltrimethoxysilane?KH540?.The structure of CLNH₂-DOPO-POSS was confirmed by Fourier transform infrared spectroscopy?FTIR?,NMR spectroscopy(¹HNMR and ²⁹Si-NMR),MALDI-TOF and XRD.Thermal stability,mechanical properties and flame retardancy effect of CLNH₂-DOPO-POSS on epoxy resin were comprehensively evaluated via TGA,DMA,universal tensile testing,LOI and UL-94.The flame-retardant mechanism of the EP modified with CLNH₂-DOPO-POSS was investigated by TGA-IR,TGA-MS and scanning electron microscopy.The thermally cured epoxy resins with CLNH₂-DOPO-POSS possed enhanced thermal,mechanical and flame retardant properties.Tensile and flexural strength increased to 82.8 MPa and 105.1 MPa from 69.9 MPa and 99.3 MPa,18.2%and 7.8%higher,respectively,than those of the control epoxy resin.The T_g can reach up to 183.8^oC.At a loading of only 3 wt%CLNH₂-DOPO-POSS,the LOI value can reach up to 31.9%and UL-94 V-0 standard test has been achieved.The flame-retardant mechanism was attributed to the char reinforcing effect of silicon,the catalytic charring effect of DOPO and the H radicals capture effect of DOPO.