Syntheses Of Four Novel Phosphorus-nitrogen Containing Flame Retardants And Their Application In Epoxy Resins

Epoxy resins have been widely applied in various fields, such as electricappliances, integrated circuits, etc. But inflammability is a flaw for epoxy resins, whichlimits their application severely. Therefore, flame-retarding modification for epoxyresins has become a key issue. In this thesis, phosphorus-nitrogen-containing flameretardants were prepared, and their performance was characterized.Two series of flame retardants were synthesized by two steps. The first series offlame retardants: syntheses of two imines BDBB and BDBP through condensationreactions between3,4-dihydroxybenzaldehyde and4,4’-diaminobiphenyl,3,4-dihydroxybenzaldehyde and1,4-phenylenediamine, the yields were90%and80%,respectively; Then addition reactions between9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and the two iminesrespectively, and the flame retardants BDBB-DOPO and BDBP-DOPO were obtainedwith the yields of85%and80%respectively. And the second series of flame retardants:two imines BPA and BBA were acquired by the reactions of4-aminophenol with1,4-phthalaldehyde and4,4’-biphenyldicarboxaldehyde, respectively, and the yieldswere80%and90%, respectively; Then flame retardants BPA-DOPO and BBA-DOPOwith the yields of95%and93%respectively were synthesized by the reactions ofDOPO with imine-containing intermediates BPA and BBA, respectively. They all werecharacterized by FTIR, NMR and MS. And the flame retardants were used to reactwith epoxy resins and the epoxy thermosets were obtained.The thermal stability and thermal degradation of the epoxy systems weredetermined by thermal gravimetric analyses (TGA). With the addition of phosphoruscontents, the char yields increased gradually, and the char yields were all more than22%, but the thermal decomposition temperature of5%weight loss (Td) decreasedgradually. With the same phosphorus content, the Tdvalues and char yields of theepoxy thermoset BDBB-DOPO were higher than those of the epoxy thermosetBDBP-DOPO, the char yields of the epoxy thermoset BBA-DOPO were higher thanthat of the epoxy thermoset BPA-DOPO, and little difference between the Tdvalues ofthe epoxy thermoset BPA-DOPO and BBA-DOPO. The glass transition temperature (Tg) of the epoxy thermosets were tested bydifferential scanning calorimeter (DSC). The Tgvalues were all more than130℃, andwith the increasing of phosphorus content, the Tgvalues reduced slowly. With identicalphosphorus content, the Tgvalues of the epoxy thermoset BDBB-DOPO were higherthan that of the epoxy thermoset BDBP-DOPO, and the Tgvalues of the epoxythermoset BBA-DOPO were higher than that of the epoxy thermoset BPA-DOPO.Through the UL94test and the limiting oxygen index (LOI) test. Four epoxythermosets reached UL94V-0rating with the phosphorus content of1.0wt.%. The LOIvalues of the epoxy systems became higher with the phosphorus content increasing,and the LOI values were all more than35.8.