Preparation Of Cyclotriphosphazene Derivatives And Its Effect On Thermal Properties Of Epoxy Resins

In this paper,hexachlorocyclotriphosphazene(HCCP)used as the basic raw material was reacted with a variety of nucleophilic reagents.Two types of cyclotriphosphazene compounds were synthesized by varied reactions such as nucleophilic substitution,oxidation,hydrolysis,addition etc.The first type was called non-spirocyclic compound which included the same nucleophile linked to three phosphorous atoms of the phosphazene.The second type was called spirocyclic compound which included single spirocyclic and double spirocyclic that were capped with different numbers of biphenols.Finally,three kinds of flame retardant epoxy resins were prepared by selecting three kinds of compounds filled to the epoxy resin.(?)Non-spirocyclic compound:(1)HCCP as a basic material was reacted with p-hydroxybenzaldehyde and p-nitrophenol by nucleophilic substitution reactions under the conditions of K2CO3 as an acid-binding agent respectively to obtain two kinds of hexa-substituted products 6Q and 6N.The structure of 6Q and 6N were confirmed by FTIR,1H NMR and 31P NMR.(2)H2O2 as the oxidant under alkaline condition,the-CHO of 6Q was oxidized to-COOH to form the compound 6QO which was characterized by FTIR,'H NMR and31PNMR.(?)Single spirocyclic compound:(1)Biphenol was used as a modifier of HCCP to synthesize T1 compound containing four P-Cl bonds.Then T1 was reacted with p-hydroxybenzaldehyde and p-nitrophenol respectively to synthesize two single spirocyclic compounds T1Q and TIN which were confirmed.(2)Compound T1QO was synthesized by oxidizing from-CHO of T1Q to-COOH,and its structure was characterized by FTIR,'H NMR and 3"P NMR.(3)The crystal of compound T1Q was cultivated which was analyzed by X-ray single crystal diffraction.(?)Double spirocyclic compounds:(1)compound T2 containing two P-Cl bonds was synthesized from HCCP and biphenol.And then T2 was reacted with p-hydroxybenzaldehyde and acetaminophen respectively to synthesize two types of double spirocyclic compounds T2Q and T2X.Their structure was characterized by FTIR,1H NMR and 31P NMR.(2)The compound T2X was hydrolyzed to synthesize a double spirocyclic compound T2XH containing four amino groups.The target compound also passed the structural characterization.(IV)Different proportions of 6Q as an additive flame retardant was added to epoxy resin(E-44,EP)with 4,4'-diaminodiphenylmethane(DDM)as the curing agent to prepared the flame retardant epoxy resin 6Q/EP.Its performances were tested by thermogravimetry(TG),Limiting oxygen index(LOI)etc.The result of TG showed that the addition of 6Q not only increased the initial decomposition temperature of EP,but also significantly promoted the production of carbon residue at high temperature.Limiting oxygen index(LOI)suggested that 6Q had good flame retardant efficiency for EP.Among them,when the phosphorus addition amount was only 0.5%,the LOI value increased by 16.1%.And the maximum LOI reached 31.5,which showed excellent flame retardancy.Scanning electron microscope(SEM)of the residue showed that there were more cracks and holes in the residual carbon of pure EP which was relatively loose.But the residue of 6Q/EP was denser and more uniform,which can protect the material from further degradation.(V)E-44 EP was filled by 6N to prepared flame retardant resin 6N/EP whose performances were tested.The result showed that the addition of 6N improved the performance of EP which showed good flame retardancy.The SEM of the residue suggested that the residue surface was dense and uniform.(VI)TlQ was also used as a flame retardant to prepare TlQ/EP(E-44)with DDM as the curing agent · And Its performances were tested.The result of TG showed that the TlQ itself had good thermal stability and char formation.LOI showed that TlQ had a good flame retardant effect on EP.However,flame retardant effect of T1Q was slightly lower than 6Q.The reason is that 6Q containing more aldehyde groups could form more dense cross-linked structures,and the high carbon content of biphenyl has less effect on carbon formation than that of the impact of the network of aldehyde groups.Moreover,it can be seen from the macro analysis of the residue that the addition of T1Q promoted a large amount of carbon layer after the burned TlQ/EP-1.0.The carbon layer protected the EP matrix and reduced the EP temperature.