Study On Thermal Stability And Thermal Decomposition Mechanism Of 1-((cyano-1-methylethyl)azo) Formamide

Polymers are essential chemical materials in the world today.About 40%-45%of industrial polymers are produced by free radical polymerization.Azo initiators have become the most important radical initiator due to the advantages of first-order reaction and product stability.However,in a high-temperature environment,azo initiators are less safe and prone to decomposition reactions and release enormous heat and gaseous.1-（（Cyano-1-methylethyl）azo）formamide（CABN）is an azo initiator with high heat sensitivity and self-reactivity.Due to the instability of the N-R bond of the azo initiator,improper operation,incompatible materials,and other dangerous situations,thermal explosion accidents may occur during the manufacture,storage,and transportation of CABN.Therefore,this paper combines experiments with simulation to study the thermal stability and thermal decomposition mechanism of CABN under the influence of pure CABN and impurities.In this paper,firstly,the differential scanning calorimeter（DSC）was used to obtain the DSC curve of pure CABN and CABN mixed with water and urea under air atmosphere to obtain the initial reaction temperature（₀）,the maximum exothermic temperature(₈)),the termination reaction temperature(₀9)（9）),the heat of reaction（?H）,and other thermodynamic parameters.Simultaneously,according to the thermodynamic equations Kissinger equation,Flynn-Wall-Ozawa equation,and Starink equation,the corresponding activation energy of chemical reaction was calculated to judge the danger further.On this basis,the DSC data of CABN and other azo initiators were compared.The thermogravimetric-mass spectrometer（TG-MS）was then used to determine the weight loss stages of CABN and their corresponding gaseous products.At the same time,the infrared spectrometer（IR）was used to obtain the decomposition residues at a specific temperature under each weight loss stage.Finally,the Gaussian software was used to simulate the possible thermal decomposition reaction path of CABN to obtain the optimal thermal decomposition path.The Mulliken charge,Fukui index,and front-line orbit of pure CABN and CABN under the influence of additives were simulated by Materials Studio software to judge the influence of additives on the thermal stability of CABN.Compare the above simulation results with the experimental results for verification.The research results show that（1）CABN began to decompose exothermically at about120℃.The average heat release was 1418.4 J/g.The hazard level wasⅢ.The potential explosion risk was very high.The average activation energy obtained by the thermodynamic equation was 33.202 k J/mol.（2）The exothermic decomposition reaction of CABN was violent when a small amount of water was added.₀ lagged slightly,and the average value ofdropped to 1085.9 J/g.The CABN hazard level was changed to II,and the potential explosion hazard was very high.The average value of₍（6） of CABN was 27.268 k J/mol,which was smaller than the average value of₍（6） of pure CABN.CABN was less safe and more prone to thermal runaway.（3）With the increase of water,thevalue of CABN continued to decrease.A large amount of water will reduce the enormous heat generated by CABN,so CABN accidents can be treated by sprinkling water.（4）The addition of urea promoted the overall advancement of the thermal decomposition of CABN and caused the decomposition reaction to being more violent.The average₍（6） of CABN added with urea was 22.065 k J/mol,which was smaller than the average₍（6） of pure CABN.CABN becomed active,and thermal runaway was more likely to occur.With the increase of urea,the₀ of CABN gradually decreased,and the average value ofwas 971.8 J/g.Therefore,the amount of urea added must be strictly controlled.（5）Through the TG-MS experiment,it can be concluded that CABN had experienced four stages of weight loss with the increase of temperature.The first weight loss stage was the central reaction part of the exothermic stage.The second stage of weight loss was the completion stage of heat release.The gaseous products in the whole decomposition reaction included N₂,CO,NH₃,CO₂,and HNCO.（6）IR experiments were carried out at 150℃,180℃,and 280℃.It can be inferred that the whole thermal decomposition reaction products included urea,2-aminoisobutyronitrile,ammonia（NH₃）,isocyanic acid（HNCO）,and isobutyronitrile.（7）By comparing the DSC data of CABN and other azo initiators,it can be concluded that among the seven azo initiators,CABN had the lowest safety and was more prone to thermal explosion accidents.Simultaneously,the addition of water,urea,HCl,and Na OH will increase the thermal risk of CABN.（8）Gaussian software was calculated that the thermal decomposition of CABN would first produce a large amount of N₂,accompanied by the generation of CO and CO₂.The produced urea will be further decomposed into ammonia and isocyanic acid.At the same time,2-aminoisobutyronitrile（C₄H₈N₂）and isobutyronitrile（C₄H₇N）were formed.From a safety point of view,high temperature will cause the chemical bonds of CABN molecules to break and thermal decomposition reactions occured.Thermal decomposition generated gaseous and free radicals while releasing enormous heat.The heat increased sharply but cannot be effectively released,which leads to the occurrence of thermal runaway accidents.（9）In the Materials Studio simulation,it can be judged by Mulliken charge,Fukui index,and front-line orbit that the addition of water,urea,HCl,and Na OH will increase the chemical stability of CABN,thereby increasing the thermal stability of CABN.The simulation results were consistent with the experimental results.Through experiments and mechanism research on CABN,the thermal stability and thermal decomposition mechanism of CABN were analyzed.The research results can provide safety guidance measures for its production,transportation,use,and storage.