Synthesis Of Curing Agent Containing Phosphorus Imidazole Derivatives And Properties Of Flame-Retardant Epoxy Resin

In the application scenarios of thermosetting polymers,such as building materials,thermal insulation materials or daily necessities,it is very necessary to have the characteristics of heat resistance,flame retardancy and low water absorption.In view of the problems such as the decline of mechanical properties and poor compatibility with the matrix of traditional additive flame retardants,starting from the molecular structure design,this thesis combines the imidazole derivatives with curing activity and phosphorus flame retardants to synthesize two kinds of flame retardants.It is a phosphorus-containing imidazole derivative curing agent,and is used for epoxy resin（EP）curing and flame retardant.The main research contents are as follows:（1）Using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）,2-aminobenzimidazole and hydrogen peroxide as raw materials,a flame retardant curing agent（DPBM）containing DOPO structure was successfully synthesized through a two-step reaction,and cooperated with 4,4-diaminodiphenylmethane（DDM）to participate in the curing and curing of epoxy resins.Flame retardant.Since DPBM has multiple cross-linking sites,it can carry out curing reactions in multiple directions.On the one hand,DPBM can accelerate the curing reaction of epoxy resins,reduce the peak temperature of curing exotherm,and on the other hand,it also increases the cross-linking.Density and storage modulus and the mechanical properties of the cured product were not significantly reduced by the addition of DPBM.Moreover,thermogravimetric（TG）,flame retardant properties and cone calorimetry（CC）analysis show that the heat resistance and carbon-forming ability of DPBM are higher than those of DOPA and DOPO;only 1 wt%phosphorus content can make the epoxy resin system pass the V-0 grade,and the limiting oxygen index（LOI）increases.Compared with the pure EP system,peak heat release rate（PHRR）,the average heat release rate（AHRR）and the combustion index（FIGRA）of EP/DPBM-1.0 were reduced by 46.6%,34.6%and 26.4%,respectively.Finally,the two-stage mechanism can be used to reveal the flame retardancy principle of the flame retardant.In the condensed phase,a large amount of coke slag prevents the exchange of mass and heat during the combustion process,and also hinders the release of combustible gases into the combustion zone;in the gas phase,the generated phosphorus and phosphorus-oxygen radicals capture active radicals（Hydrogen Radicals and Hydroxyl Radicals）,thereby ending the combustion chain reaction.（2）Past studies have shown that epoxy resins tend to compromise in terms of heat resistance and latency while improving flame retardancy and mechanical properties.Therefore,a new type of flame retardant curing agent（IPDPP）was synthesized by using imidazole,p-hydroxybenzyl alcohol and diphenylphosphinic acid chloride as raw materials,and used for curing and flame retardant epoxy resin and improving the latent of epoxy resin.sex.The analysis results show that:IPDPP has good curing activity and thermal latency,and the cured EP exhibits good heat resistance.When the phosphorus content of EP is 1.5 wt%,the T_5%of the EP/IPDPP-1.5 sample is 340.4℃,which is 17.4%higher than that of pure EP and 4.2%lower than that of the EP/IPDPP-0.9 sample.Moreover,due to the existence of a large number of rigid benzene rings,the cured EP/IPDPP sample has mechanical properties comparable to pure EP,and the glass transition temperature is slightly increased;the addition of flame retardant can make the LOI of EP/IPDPP-1.5 reach 32.5%,UL-94 passed V-0 rating.The CC test showed that total heat release rate（THR）,PHRR,and average carbon dioxide yield（av-CO₂Y）of the EP/IPDPP-1.5system were reduced by 29.7%,52.2%,and 69.1%,respectively,compared with pure EP.Further research found that the flame retardant properties of EP/IPDPP samples are achieved by the heat insulation and oxygen isolation effects of IPDPP and the gas free radical quenching reaction.In addition,the addition of IPDPP reduces the water absorption and dielectric loss factor of EP to a certain extent.The two flame retardant curing agents synthesized above can be well applied to epoxy resins and exhibit different degrees of excellent properties,such as:flame retardant,improved mechanical properties,improved latent properties,and optimized heat resistance.In summary,the two flame retardants have certain industrial application value in the field of epoxy resin.