Preparation Of DOPO-Based Phosphorus/Silicon/Nitrogen-Containing Oligomeric Flame Retardants And Their Application In Hydrocarbon And Epoxy Resins

In order to comply with green and sustainable development,and to obey the prohibition of halogen-containing flame retardants in domestic and international laws,the development of halogen-free flame retardants has become a hot spot in the field.Among them,9,10-dihydro-9-oxo-10-phosphafi-10-oxide（DOPO）with a phosphorus heterophosphate ring structure,has higher thermal and chemical stability compared with traditional organophosphates.Phosphorus-containing flame retardants based on DOPO have attracted much attention in recent years.These macromolecular DOPO-containing phosphorus-nitrogen and phosphorus-silicon composite flame retardants,have become one of the current hot spots in the field of flame retardants.Because these additives not only retain the advantages of the widely used additive flame retardants,but also improve the poor compatibility between additives and polymer.Styrene-butadiene thermoplastic elastomers（SBCs）and epoxy resins（EPs）are commonly polymer materials in the field of electronic packaging,with good processing properties.However,because of their inherent high flammability,these materials have great safety hazard,therefore they need to be modified by flame retardants.The development of new phosphorus/nitrogen/silicon composite flame retardants with good compatibility with polymeric matrix has important practical value for the flame retardant modification of the above-mentioned resin systems.In this study,using DOPO as the synthetic building block,two types of additive phosphorus-silica and phosphorus-nitrogen composite flame retardants were respectively synthesized via the free radical addition or nucleophilic addition reaction.The above two flame retardants were added respectively to styrene-butadiene two-block copolymers（PSB）or epoxy resins（EP）,and the effects on the thermal stability,flame retardancy or dielectric properties of PSB or EP resins were investigated.The main studies are as follows:1.A greener preparation method of caged oligomeric silsesquioxane（DOPO-POSS）was developed and used to improve the flame retardancy and dielectric properties of GF-PSB.Although there are many types of flame retardants available in the market,there are few flame retardants that can meet the requirements of both good flame retardancy and excellent dielectric properties.However,the Dk and Df value are the key parameters for copper-clad substrates.In view of the excellent dielectric properties,good thermal stability and mechanical strength of POSS,the synthesis of phosphorus-silicon synergistic flame retardant by introducing DOPO into POSS is expected to obtain good flame retardancy and dielectric properties at the same time.In this chapter,the existing preparation methods of DOPO-POSS were improved,the structure of DOPO-POSS was characterized by FT-IR,NMR and MS.The thermal properties of DOPO-POSS were investigated by DSC and TG.The results showed that the purity,yield and thermal stability of DOPO-POSS obtained by this improved procedure are improved,compared with those obtained by the methods reported in the literature.The chlorine content met the“halogen-free”requirement.The synthesized DOPO-POSS was added to the GF-PSB system by the physical mixing method.The effects of DOPO-POSS on the flame retardant properties,thermal stability and dielectric properties of the GF-PSB composite were investigated.The residual carbon after combustion was analyzed by SEM.The results showed that DOPO-POSS and PX-200 effectively improved the thermal stability and flame retardancy of GF-PSB,and GF-PSB/DOPO-POSS performs better.For GF-PSB/DOPO-POSS-10 composite,the char residue at 555 ^oC increased from 16.8%to 80.8%,LOI increased to 51%and reached UL-94 V-1 rating,effectively inhibiting the burning drip.In terms of the inhibition of heat and smoke,DOPO was weaker than PX-200 in the GF-PSB system.The reasons behind these improvements are discussed from the view of the structure-property relationship and the matching of additives and resin matrix.Of particular importance is that under 10 GHz,the average Dk and Df of GF-PSB/DOPO-POSS was 3.34 and 0.00293,respectively.Its dielectric properties are better than those of commercial flame retardant PX-200,reach the industry standard for ultra-low Df.It is a potential high-performance CCL material with great commercial prospects.2.New carbon-forming agents of phosphorus-nitrogen oligomeric based on DOPO,MDI and hindered phenols were synthesized and applied in the epoxy resins.Hindered phenols are a class of free radical quenchers,which contains a large number of benzene rings and hydroxyl groups,which would have high carbon formation rate and abundant reaction sites.In this chapter,two new phosphorus-nitrogen oligomeric charring agents（DMPMP and DMPPA）were synthesized by the addition reactions of DOPO,isocyanate（MDI）and two hindered phenols（poly（4-methoxyphenol）and poly（pyrogallic acid））,respectively.The structures and properties of DMPMP and DMPPA were characterized by FT-IR,NMR,GPC,TGA and water contact angle test.The results showed the water resistance,thermal stability and carbon residue rate of the synthesized oligomeric charring agents（DMPMP and DMPPA）were obviously improved.A series of cured epoxy resins were prepared by compounding melamine polyphosphate（MPP）with either of the two charring agents.The experimental results showed that compared with the pure EP,the thermal decomposition temperature of the flame retardant EP decreased and the rates of carbon formation was increased obviously.In the binary intumescent flame retardant（IFR）system,the limited oxygen index increased with the increase of the addition of the charring agent DMPMP or DMPPA.The flame retardant effect of DMPPA/MPP system was slightly higher than that of DMPMP/MPP system,and the LOI of EP/MPP₁₂/DMPPA₈ increased from 19.3%to 25.6%.