Study On Synthesis And Flame-Retardant Effect Of DOPO-containing Diglycidyl Ether

Epoxy resins are widely used in a variety of industrial applications,thanks to their several desirable properties.However,one of the main drawbacks of epoxy resins like many other polymers is inflammability,which limits their application in the electrical and electronics industry.Traditionally,halogenated flame retardants are widely used but have become less attractive,owing to toxicity and environmental concerns.As a result,the development of halogen-free flame retardants,especially DOPO derivatives have attracted considerable attention because of their versatile flame extinguishing behavior.Among many researches,after the introduction of DOPO-containing flame retardants,the deterioration of Tg,lower curing activity,negative impact upon thermal resistance and waterlogging tolerance may ensue.What's worse,some excellent flame retardants rely on complex synthetic process and high costs.In this work,a kind of DOPO-containing diglycidyl ether DPBAEP was synthesized through the etherification of a multidimensional DOPO-containing biphenol DPBA.DPBA has the good nucleophilicity of its phenolic group because of the bisphenol A-like structure.We indicated their structure as well as purity by the FTIR and NMR spectra,the elemental analysis,the melting point test and epoxide number.The proposed mechanism for the synthesis of DPBA and DPBAEP was analyzed.TG analysis shows the substantial thermal stability of DPBAEP.And the yield is about 90%after the process optimization.The characterization of the curing behavior of the thermosetting system consisting of DPBAEP and DDS was performed by dynamic DSC scans,and the waterlogging tolerance of the thermosets were studied.The activation energies calculated from Kissinger's approach and Ozawa's approach are 66.9 kJ·mol-1 and 71.3 kJ·mol-1 for DPBAEP/DDS,which are a little higher than DGEBA/DDS.The Tgs of DPBAEP/DDS and DPBAEP/DDM thermosets are as high as 233? and 211?.Compared with DGEBA thermosets,the DPBAEP thermosets have lower maximum decomposition rate,remarkable higher char yields,and 0.04%higher on moisture rate.Then,DPBAEP was used to improve the flame retardancy of TGDDM epoxy resin system cured with DDS.The thermal properties,flame-retardant effect and flame retardation mechanism were investigated.The sample achieves UL-94 V-0 rating with over 5 wt.%DPBAEP,and generates a firm and intumescent char barrier.The char layer exhibits a continuous and contoured structure with a lustrous surface.After the addition of 15 wt.%DPBAEP,LOI value of the sample levels from 29.1%up to 33.4%significantly,where the phosphorus content is as low as 0.5 wt.%.As a result,DPBAEP shows great potential to impart flame retardancy and a strong self-extinguishing capacity to TGDDM epoxy resin at very low loading.We use DPBAEP and OMMT modified with 3-glycidoxypropyltrimethoxysilane(KH-560)to improve the flame retardancy of DGEBA epoxy resin.The flame-retardant effect and thermal properties were investigated,especially the synergistic flame retardation mechanism.After the addition of 15 wt.%DPBAEP and 1 wt.%OMMT,LOI value of the sample levels from 22.9%up to 31.7%significantly,and achieves UL-94 V-0 rating,which shows even the better flame retardancy than the sample with 20 wt.%DPBAEP.We can observe honeycomb structure of the char layer investigated by SEM analysis.Otherwise,the phosphorus moieties and Si-O structure remain in the carbonaceous char,which played an important role in improving the stability of char yield.It is deduced that DPBAEP is an eco-friendly halogen-free flame retardant,and shows great potential to impart flame retardancy to common epoxy resins at very low loading.What's more,the application of DPBAEP exhibits several desirable properties,such as excellent compatibility with epoxy resins,nonmigratory performance,less negative impact upon waterlogging tolerance and thermal properties.