| In recent years,DOPO derivatives with excellent flame retardancy,thermal stability,good organic solubility and environmental friendliness,have attracted more and more attentions in phosphorous-containing flame retardants.In this paper,two kinds of novel DOPO derivatives flame retardants were designed and synthesized,one is high-phosphorus-content phosphaphenanthrene compound ABD,which has functional group-hydroxyl;the other is cluster-like crosslinking aggregated biobased-phosphaphenanthrene macromolecule P-DCAD.Then,ABD and P-DCAD were applied to flame retardant epoxy resin,respectively.Their working modes and mechanisms were explored,and the flame retardant properties of epoxy resin and their flame retardant mechanism in gas phase and condensed phase were also studied.The main research contents are as follows:(1)A novel high-phosphorus-content flame retardant ABD with hydroxyl was synthesized via addition reaction between DOPO and acrolein,and then its structure was characterized and confirmed.ABD was applied to DGEBA using 4,4'-diamino-diphenylmethane(DDM)and 4,4'-diamino-diphenylsulfone(DDS)as curing agent,respectively.The flame retardant behavior and mechanism of ABD/EP system were investigated.It was found that the epoxy resin performed excellent flame retardant performance at a lower loading amounts of ABD.When the amounts of ABD were only3 wt.%,3%DCAD/EP/DDM specimen obtained a LOI value of 36.2%and passed the UL94 V-0 rating test;when the amounts of ABD were 10 wt.%,10%DCAD/EP/DDS specimen obtained a LOI value of 29.7%and reached UL94 V-1 rating.In the combustion process,ABD can inhibit the combustion intensity of the matrix,and effectively reduce the production of pk-HRR,THR and av-EHC in the ABD/EP system.Meantimen,the mechanism of ABD flame retardant epoxy resin was also revealed:Under the lower addition amounts of ABD,the combination effect of phosphaphenanthrene group which has original flame retardant effect and hydroxyl group which has promoting charring effect endowed epoxy resin with better flame properties.In addition,the flame retardant efficiency of ABD and DOPO in epoxy resin was compared.It was found that the flame retardant efficiency of ABD/EP system was higher than that of DOPO/EP system at the same adding amounts.(2)A cluster-like crosslinking aggregated biobased-phosphaphenanthrene macromolecule P-DCAD was synthesized by olefin copolymerization using diene structure biobased-phosphaphenanthrene compound DCAD as monomer,and its structure was characterized and confirmed.Then,P-DCAD was applied to DGEBA using DDM as curing agent and P-DCAD/EP system flame retardant behavior and mechanism were studied.The results exhibited that P-DCAD not only endowed epoxy resin with excellent flame retardancy and self-extinguishing ability,but also improved excellent heat resistance and physical mechanical properties.When the amounts of P-DCAD were 4 wt.%,the vertical combustion test of the specimen passed V-0 rating,and 33.4%LOI of the specimen was obtained.During combustion,P-DCAD can inhibit the combustion intensity of the matrix,and effectively reduce the production of pk-HRR,THR and av-EHC in P-DCAD/EP/DDM system.The heat resistance of 4%P-DCAD/EP/DDM system was significantly improved.The glass transition temperature was increased to 178.49?and the HDT temperature raised to 170.6?.The impact strength of 4%P-DCAD/EP/DDM rise to 22.16 k J/m~2,109.1%higher than that of 4%DCAD/EP/DDM sample,and the storage modulus increased from 6472 MPa to 7126MPa at 40?.In addition,the flame retardant mechanism and toughening mechanism of P-DCAD in epoxy resin were analyzed.The results showed that P-DCAD had the same flame retardant mechanism for epoxy resin as DCAD.The toughening mechanism were deduced that:1)P-DCAD can react with epoxy groups as a part of curing agent,thus improving the ability of the absorbing energy in process of material fracture;2)the polarity of phosphaphenanthrene groups of P-DCAD enhanced the molecular interaction between the flame retardant and the matrix. |
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