Preparation Of Modified DOPO Contained Cyanate Ester And Study On Synergistic Flame Retardant Effect

Cyanate ester forms s-triazine structure which leads to some sort of improvement in thermostability and polarization resistance during the curing reaction.The high crosslinked network provide CEs higher glass-transition temperature and lower dielectric constant and loss over a wide frequency range than that of commercial epoxy resins.Therefore Cyanate esters(CEs)attract much attention in the applications of electronic materials and aircraft However cyanate esters as a thermoset resin is still flammable which hinders its application in electronic application.For the purpose of improving the flame retardancy of CEs,different flame retardants such as halogen-,phosphorus-,sulfur-,silicon-containing compounds and inorganic fillers are combined with cyanate esters.As a consequence of halogen flame retardants leading to safety and environmental problems during combustion,nowadays halogen-free flame retardant has been developed and used widely.Previous reports have pointed out that 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide(DOPO)is a reactive halogen-free flame retardant which can react with cyanate ester and improve its flame retardant property.However the increasing of phosphorus content leads to the increasing of dielectric constant and loss and the reduction of glass transition temperature and initial decomposition temperature.In this paper,nitrogen contained compounds are introduced into DOPO contained cyanate esters.The synergistic effect between nitrogen and phosphorus improves the efficiency of flame retardant.The curing kinetics,thermostability,flame retardant property and dielectric constant and loss are test.The flame-retardant mechanisms are investigated by the means of LOI rate,UL-94 test and cone calorimetry test.The results are listed as follow:(1)For the purpose of introducing the triazinone structure into DOPO contained cyanate esters(CEP),triglycidyl isocyanurate(TGIC)or triallyl isocyanurate(TAIC)is blended with CEP and forming triazinone/DOPO synergy flame retardant cyanate ester resins(CEPG or CEPA).The results indicate that the promotion of phosphorus contents for CEPG blends lead to the reduction of curing temperatures which are due to the epoxy group for TGIC reacting with cyanate ester at lower temperature.The formed crosslink network lead to glass transition temperatures shift from 242 to 218?as the phosphorus contents increase from 0.5 to 2.0,which is higher than that of CEPA with the same phosphorus contents.TAIC contained allyl group which is homopolymerized during the curing of CEP resin.Therefore the curing temperatures slightly reduce to lower temperature which is due to the catalyst of DOPO.The IPN network lead to crosslink density of CEPA resin much lower than that of CEPG,so that the glass transition temperatures shift from 234?to 148?.For CEPG resin,TGIC and DOPO degrade and release noninflammable gas and phosphaphenanthrene compound at the same time during the combustion.The synergistic effect between triazinone structure and DOPO occur.The synergistic effect is also observed for CEPA resin when the phosphorus content is lower than 1%.However when the phosphorus content is higher than 1%,the synergistic effect disappears which is attribute to TAIC and DOPO degrade at different temperature ranges.The dielectric constant and loss of CEPG resins are lower than that of neat CE resin but higher than that of CEPA resin.(2)A phosphorus-containing maleimide flame retardant(BDMP)is synthesized via the addition reaction between N,N'-bismaleimide-4,4'-diphenylmethane and DOPO.The structure of BDMP is characterized by Fourier-transform infrared spectroscopy(FTIR),¹H and ³¹P nuclear magnetic resonance and elemental analysis.The curing kinetics,thermal,flame-retardant and dielectric properties of CE-BDMP resins are investigated.The results indicate that the curing temperatures shift to lower temperature due to the catalyst of BDMP.As BDMP contain only one maleimide group leading to reduction of crosslink density,the glass transition temperatures of CE-BDMP resins decrease from 260?to 216?.The initial decomposition of modified CE-BDMP resins shift from 416?to 363?,and on the contrary,the char yield increased from38.8%to 44.5%,which is attribute to BDMP degrade at lower temperature and result in higher char yield.CE-BDMP-1.0 resin acquired LOI value of 37%and achieved a UL-94 V-0 rating.The dielectric constant of CE-BDMP is 2.96-3.02 which is lower than 3.03 for neat CE resin at 1GHz.BDMP is a flame retardant providing not only improvement of flame retardant property but also improvement of dielectric constant and loss.(3)Novel phosphorus-contained Schiff base(PSF)is synthesized by furfurylamine,salicylaldehyde and DOPO and is incorporated with CE to prepare a flame-retardant cyanate esters(CE-PSF).The structure of PSF is characterized by Fourier-transform infrared spectroscopy(FTIR),¹H and ³¹P nuclear magnetic resonance and elemental analysis.The curing kinetics,thermal,flame-retardant and dielectric properties of CE-PSF resins are investigated.The results indicate that the curing temperatures of CE-PSF resin shift to lower temperature under the catalyst of the phenolic group and imino group for PSF,leading to the reduction of activation energy.The reduction of crosslink density for CE-PSF leads to the glass transition temperature decrease from 272?to235?.The initial decomposition of modified CE-PSF resins shift from 419?to 381?,and on the contrary,the char yield increased from 40.4%to 47.1%.The incorporating of PSF into CE resin leads to improvement in flame retardant property.When the phosphorus content is 1.0%,CE-PSF-1.0 achieve LOI of 35%and UL-94 V-0 rating.The dielectric constants and dissipation factors of CE-PSF increase with the promotion of phosphorus contents and slightly lower than neat CE for forming more s-triazine network with the catalysis of PSF.For PSF structure contains DOPO structure as acid source,imino group as amine source and furan group as carbon source,which consist of the basic factors for intumescent flame retardant,and the synergistic effect occurs between the phosphorus and nitrogen.