| UV curable adhesives are characterized by low energy consumption,fast curing rate and good spreading ability,but flame retardant modification is a major problem for the flammability of cured products.The main methods used for flame retardant modification are"additive" and "reactive".The additive flame retardant adhesives have lots of shortcomings—poor compatibility,more internal interfaces of cured materials,poor mechanical properties and easy precipitation of flame retardants and so on.The reactive flame retardant adhesives prepared by the prepolymer with performance of flame retardant modified by grafting reaction or copolymerization can fundamentally avoid the above problems.In this study,with polydiethylene glycol adipate(PDEGA3000),Methylene-bis(4-cyclohe-xylisocyanate)(HMDI)and 2-Hydroxyethyl acrylate(HEA)as the main material,1,6-Hexanediol diacrylate(HDDA)as the active diluents,polyurethane acrylate(PUA)was synthesized.With the flame retardants FRC-2(3-[(hydroxymethyl)amino]-3-oxopropyl phosphonic acid-dimethyl ester),FRC-6(N,N-bis(2-hydroxyethyl)aminomethyl phosphonic acid diethyl ester)introduced into PUA by grafting reaction,copolymerization modification respectively,the phosphorous branched polyurethane acrylate(P-PUA1)and phosphate-containing skeleton polyurethane acrylate(P-PUA2)were prepared.The products were characterized by FT-IR and GPC.The effects of the synthetic process,the amounts of catalyst(DBTDL)and polymerization inhibitor(MEHQ),and the ratio of monomer on the structure,molecular weight and its distribution of this three prepolymer were studied.Finally,a reactive flame retardant UV curable adhesives were prepared.The effect of active diluent(HDDA)content on its mechanical properties was discussed by means of hardness and shear strength.The effects of prepolymer ratio on thermal stability and flame retardancy were studied by TG,LOI and vertical combustion tester.The results are as follows.(1)The synthetic process of PUA:n(HMDI):n(pDEGA3000):n(HEA)=2.2:1:2(the monomer ratio),the amounts of DBTDL,MEHQ and HDDA are 0.3%,0.3%and 20%respectively,the chain extension reaction is at 55℃ for 2 hours and then 60℃ for 1 hour,the esterfication is at 70℃for 2 hours and then 75 ℃ for 1 hour.The Mn and PDI of PUA reach to 6516 g mol-1and 1.30,respectively.(2)The synthetic process of P-PUAi:n(HMDI):n(PDEGA3000):n(FRC-2):n(HEA)=2.3:1:1:1(the monomer ratio),the amounts of DBTDL,MEHQ and HDDA are 0.3%,0.2%and 20%respectively,the chain extension reaction is at 55℃ for 2 hours and then 60℃ for 1 hour,the first esterfication is at 70℃C for 1 hour and then 75 ℃ for 1 hour,the second esterfication is at 80℃ for 1 hour.The Mn and PDI of P-PUAi reach to 7159 g·mol-1 and 1.53,respectively.(3)The synthetic process of P-PUA2:n(HMDI):n(FRC-6):n(HEA)=2.05:1:2(the monomer ratio),the amounts of DBTDL,MEHQ and HDDA are 0.45%,0.3%and 20%respectively,the chain extension reaction is at 50℃ for 2 hours and then 60℃ for 1 hour,the esterfication is at 75℃for 2 hours and then 85℃ for 1 hour.The Mn and PDI of P-PUA2 reach to 1768 g mol-1 and 1.02,respectively.(4)The influence of reactive diluent dosage and the prepolymer ratio on the adhesive properties had been discussed,the results show that:UV curable adhesive has best overall performance when the mass ratio is PUA:P-PUA1:P-PUA2=1:1,w(Irgacure1173)=3%,W(N,N-Dimethylaniline)=2%,w(HDDA)=25%(both relative to the mass of the main resin),the content of P and N reach to 1.29%,1.32%respectively,shear strength is 7.95 MPa,hardness is 57 D.The TG tests show that Tmax1 is 302℃,Tmax2 is 392℃,T5%is 246℃,residue char yields is 10.18%,which is 453.26%higher than the PUA system.Its LOI is 25%,which is 35.14%higher than PUA system,and reaches UL94 V-2 flame retardant grade. |
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