Synthesis, Characterization And Curing Properties Of A Novel Cyclolinear Phosphazene-based Epoxy Resin For Halogen-Free Flame Retardancy

A novel cyclolinear phosphazene-based epoxy resin was designedfor halogen-free flame retardancy andsynthesized through a four-stepsynthetic route. The chemical structures of all the cyclicphosphazeneprecursors and the final objective product were confirmed by¹H and³¹P NMR spectroscopy, elementalanalysis, and Fourier transforminfrared spectroscopy. The curing behaviors of this epoxy resin withmethyltetrahydrophthalic anhydride,4,4'-diaminodiphenylmethane, andnovolak as hardeners were investigatedby differential scanningcalorimetry (DSC), and their heat resistance and thermal stabilities werealsoevaluated by DSC and thermogravimetric analysis. These thermosetsachieved a high thermal resistancedue to their high glass transitiontemperatures more than150°C, and also gained good thermalstabilitieswith high char yields. The flammability characteristics of thecyclolinear phosphazene-based epoxythermosets cured with these threehardeners were studied on the basis of the results obtained from thelimiting oxygen index (LOI) and UL-94vertical burning experimentsas well as the analysis of the residualchars collected from the UL-94test.The high LOI values and UL-94V-0classification of these epoxythermosets indicate that the incorporation of phosphazene rings into thebackbone chain imparts nonflammability to the epoxy resin owing to theunique combination of phosphorus and nitrogen following by asynergistic effect on flame retardancy. The epoxy resin obtained in thisstudy is a green functional polymer and will become a potential candidatefor fire-and heat-resistant applications in electronic and microelectronicfields with more safety and excellent performance.