Preparation Of Intrinsic Halogen-free Flame-retarded Cured Epoxy Resin Containing Phosphorus And S-triazine

Due to its excellent thermal stability, mechanical properties, insulation performance andchemical resistance, epoxy resin are widely to used in electronic device, encapsulation, andprinted circuit boards.However, like most of polymers, conventional cured epoxy product isflammable and it cannot satisfy the required properties in the field of advanced materials,which require high flame resistance.Therefore, it is necessary to prepare cured epoxy productwith good fire resistance. The reactive organo-phosphorous compounds, which are proved tohave powerful flame-retarded effect on epoxy resin by incorporated into epoxy network bycuring agents. Nevertheless, glass transition temperature (Tg), initial degradation temperatureand mechanical properties of cured epoxy productmay decreased owing to the incorporationof weak chemical bonds of P-O and P-C. So it is important to improve the flame retardedefficiency of phosphorus-containing compounds, to reduce its requirement and minimize thenegative effects on properties of cured products. Some studies indicated that a significantdevelopment of flame-retarded efficiency is noted when phosphorus element and nitrogenelement with triazine structure are present simultaneously in epoxy resin, which can bringoutstanding flame retardancy, meanwhile improve thermal and mechanical properties of curedresins. In the thesis, the cured epoxy products containing phosphorus and triazine wereprepared by phosphorus-containing epoxy resin cured by triazine-containing curing agents,and conventional epoxy resin EP828cured by curing agents with phosphorus and triazine.And the performance of cured products, including fire resistance, thermal stability,mechanical properties and dielectric performance, was investigated.Firstly,2,4,6-Tris(4-(maleimido) phenoxy)-1,3,5-triazine (TMT),2,4,6-tri-H-benzimidazole-1,3,5-s-trizaine (TRITBI),2-DOPO-4,6-bi(H-benzimidazole)-1,3,5-s-trizaine(TRISDDBI) and2,4-DOPO-6-H-benzimidazole-1,3,5-s-trizaine (TRIDDSBI) weresynthesied based on the reactions of cyanuric chloride, maleimido-phenol, DOPO andp-Hydroxy benzaldehyde. The structures of the products above were characterized andconfirmed by FT-IR,1H-NMR,13C-NMR,31P-NMR or Elmental analysis. And four type ofhalogen-free intrisic halogen products were prepared according to the chiometric ratio ofreactive groups, including that the amount of N-H functionalities of DDM was equal to thesum of epoxy groups and alkenyl groups of DOPOER and maleimido in TMT, the sumamount of N-H functionalities of TRITBI and DDM was equal to the epoxy resin groups in DOPOER, the amount of epoxy resin groups in EP828was equal to the sum amout of N-H inDDM and TRISDDBI or TRIDDSBI.Secondly, the curing kinetics of TMT-containing epoxy system was investigated and thecuring parameters were analyed. It was turned out to be that the incorporation of TMT canlower the apparent activation energy and improve the reaction rate constant, which indicatesthe acceleration effect on curing reaction of TMT. Compared to DDM/DOPOER curingsystem, the activation energy of curing reaction decreased to47.34kJ/mol from52.56kJ/molwhen the content of TMT was1.98wt%and the activation energy of curing reactiondecreased to31.90kJ/mol when the content of TMT was10.74wt%, which indicated thepromotion effect of TMT on the reaction. At the same time, N-phenyl maleimide andtri-phenoxy triazine were introduced to analyze the relationship between promotion effectsand the structure of TMT. It can be seen that both of the structure of maleimide and triazinecan accelerate the curing reaction simultaneously, but the effect of triazine was more obvious.Thirdly, the cured epoxy resin products with low content of phosphorus and triazineshowed excellent flame retardancy and all the samples passed the UL94V-0rate. Forexample, when the content of phosphorus and triazine were0.41wt%and1.02wt%,respectively, the cured products of TRISDDBI/DDM/EP828with LOI33.8%passed UL94V-0rate and total burnning time was48s. when the content of phosphorus was0.70wt%、0.77wt%and0.79wt%, and content of triazine was0.88wt%、0.85wt%and0.24wt%,respectively. LOI of cured epoxy rsin products of TRIDDSBI/DDM/EP828,TRITBI/DDM/DOPOER and TMT/DDM/DOPOER were35.6%,38.6%and41.8%,respectively. and total burining times were49.5s,42.5s and27s. Compared to the curedproducts of TRITBI/DDM/DOPOER, the cured product with maleimide showed better flameretardancy, which indicates the incoorparation of maleimide group benefits for theenhancement of flame ratardancy of cured epoxy resin product.Fourthly, the cured epoxy resin products of TRISDDBI/DDM/EP828,TRITBI/DDM/EP828, TRIDDSBI/DDM/DOPOER and TMT/DDM/DOPOER showed betterinitial degradation temperature. T5%of cured products with excellent flame retardancy were348.2°C,345.5°C,341.9°C and336.7°C, respectively. Compared to cured products ofDDM/DOPOER, T5%were increased by42.7°C,40°C,36.4°C and31.2°C. Meanwhile thecured products showed higher Tg, were171.6°C,165.8°C,150.9°C and144.8°C, respevtively, increased by33.2°C,27.4°C,12.5°C and6.4°C than DDM/DOPOER curedproduct. Compared to DDM/EP828cured products, Tgof TRISDDBI/DDM/EP828andTRIDDSBI/DDM/EP828cured products were enhanced by14.9°C and9.1°C, respectively.While Tgof TRITBI/DDM/DOPOER and TMT/DDM/DOPOER were only decreased by5.8°C and11.9°C, respectively. Therefore, the cured epoxy resin products showed higher Tgand initial degradation temperature when the curing agent contained phosphorus group andtriazine group simultaneously.Finally, the cured epoxy resin products of TRIDDSBI/DDM/EP828,TRITBI/DDM/EP828, TMT/DDM/DOPOER and TRISDDBI/DDM/DOPOER had bettertensible strength, were84.9MPa,69.6MPa,61.8MPa and60.2MPa，respectively. Comparedto DDM/DOPOER cured products, they were enhanced by25.8MPa,10.5MPa,2.7MPa and1.1MPa, respectively. And tensible strength of TRIDDSBI/DDM/EP828cured resins waseven13.1MPa higher than conventional cured epoxy resin of DDM/EP828. However, theincoorperation of triazine into the cured epoxy resin had a bad effect on the impact strength ofcured epoxy resin. Take TRIDDSBI/DDM/EP828cured product for example, its impactstrength was44.4kJ/m2, equally to the impact strenth of DDM/DOPOER, but22.2kJ/m2lower than the impact strength of DDM/EP828cured product.