Preparation and Properties of Halogen-free Fire Retardant Acrylonitrile Copolymer

Acrylonitrile(AN)-vinyl acetate(VAc) copolymer [P(AN-co-VAc) ]was synthesized via aqueous phase precipitated radical copolymerization of AN and VAc using K2S2O8-NaHSO3 as initiator.The VAc unit of P(AN-co-VAc) was selectively hydrolyzed with KOH aqueous under different pH values.The halogen-free fire retardant AN copolymer was prepared by the phosphorylation reaction among phosphoric acid,urea and the hydrolyzed P(AN-co-VAc).The structure of AN copolymer was characterized by nuclear magnetic resonance hydrogen spectrum(1H NMR),Fourier transform infrared spectroscope(FTIR),and the thermal property of them was studied by differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA).The number-average molecular weight(M n) and polydisperisity index(PDI) of the obtained P(AN-co-VAc) were determined by gel permeation chromatography(GPC).The char residue of the halogen-free fire retardant AN copolymer was analyzed by FTIR and SEM.The results show that AN is really copolymerized with VAc and P(AN-co-VAc) can be synthesized successfully.VAc unit is quickly hydrolyzed with the increase of pH.DSC indicates that with the increase of mass fraction of VAc in P(AN-co-VAc),the temperature of cyclic exothermic peak(T p) improves,and T p reaches to 328 ℃ with the mass fraction of VAc being 25%,while T p of fire retardant AN copolymer can be 340 ℃.TGA demonstrates that the char residue of fire retardant AN copolymer at 800 ℃ is 55%,which is higher than that of P(AN-co-VAc) being 41%,it fully proves that fire retardant AN copolymer has good char forming capability.The fire retardant mechanism of fire retardant AN copolymer belongs to condensed phase flame retardant mechanism.