Study On Synthesis Of Novel Phosphorus-Containing Epoxy Hardeners And Its Thermal And Flame-retardant Properties Of Cured Products

Recently, traditional epoxy molding compounds are facing great challenges forboth of the voice from ever-rising environmental protection and the requirements ofimproving the properties of electronic encapsulating materials. The conventionalepoxy resins are unable to satisfy some applications, which require higher thermalstability and good flame retardant. Aiming at the disadvantages of epoxy resin,several novel phosphorus-containing epoxy hardeners were synthesized. Theproperties of the cured polymers were investigated by several methods. Therelationship of these properties of the cured polymers with the structure of the curingagents were studied.Two novel flame-retardant curing agents for epoxy resins, DOPO-containing4-[(phenylamino)methyl]phenol (P-Ph) and DOPO-containing Mannich-type bases(P-DDS-Ph), were synthesized by the condensation of4-hydroxybenzaldehyde with4-aminophenol and DDS, respectively, followed by the addition of DOPO to theresulting imine linkage. Chemical structures of these materials were characterized withFTIR,1H-NMR spectra,31P-NMR spectra and elemental analysis. The thermalproperties and flame retardancy of O-cresol novolac epoxy resin (CNE) cured withdifferent contents of the phosphorus-containing compounds were investigated bynonisothermal differential scanning calorimetry (DSC), thermogravimetric analysis(TGA) and limiting oxygen index (LOI). The obtained results showed that theP-Ph/CNE and P-DDS-Ph/CNE have excellent flame retardancy. Moreover, theP-DDS-Ph/CNE exhibited higher T_g(224oC) and better thermal stability (T10%,345oC)than that of P-Ph/CNE. Therefore, the developed P-DDS-Ph/CNE may be potentiallyused as environmentally preferable products in electronic fields.A novel flame-retardant curing agents for epoxy resins, ODOPM-BPN wereprepared from biphenol phenol novolac (BPN) and a reactive2-(6-oxid-6H-dibenz(c, e)(1,2) oxaphosphorin-6-yl)-methanol (ODOPM) while ODOPM was synthesizedthrough the simple addition reaction between9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and formaldehyde.The chemical structure of the obtained ODOPM-BPN was characterized with FT-IR,1H NMR,31P NMR and GPC. Thermal properties and thermal degradation behavior ofthe thermosetted resin was investigated by using differential scanning calorimetry(DSC) and thermogravimetric analysis (TGA). High glass transition temperature (T_g, 194oC), good thermal properties (T10%,394oC) and high char yield (800oC,39.6%)were observed for the ODOPM-BPN/CNE cured resins. A sample containing2.58%(mass ratio) phosphorus had limiting oxygen index values of28.3which indicateexcellent flame retardancy.The research showed that CNE cured with the several novel phosphorus-containingepoxy hardeners exhabit high glass transition temperature, good thermal stability andexcellent flame retardancy. This research also provide a basis for developingphosphorus-containing epoxy resins with excellent combination property.