资源描述
单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,3.2 Initiator and Initiation,3.2.1 Types of Initiators,3.2.2 Kinetics of Initiator Decomposition,(1)Initiator Decomposition Rate,(2)Initiator Efficiency,(3)Choice of Initiator,3.2.3 Other Initiation,(1)Thermal-initiated polymerization,(2)Light initiated polymerization,(3)High energy radiation initiated polymerization,.,.,.,3.2,Initiator and Initiation,Initiation is a process which converts olefinic monomers to radicals.,Primary radicals can be produced through light,heat,or high energy radiation directly acting on monomers.,But,what used more often is initiator.,Initiators have weak bonds,Thermal decomposition can produce two primary radicals.,.,.,.,3.2.1,Types of Initiators,Azo initiator,Organic peroxide,initiator,Inorganic peroxide initiator,Redox initiation system,.,.,.,（,1,）,Azo Initiator,azobisisobutyronitrile,（,AIBN）,azo-bis-iso-heptonitrile,.,.,.,（,2,）Organic Peroxide Initiator,dibenzoyl,peroxide,dialkyl,peroxide,.,.,.,（,3,）,Inorganic Peroxide Initiator,persulphate,.,.,.,（,4,）Redox initiation system,components,：,inorganic and organic,properties,：,oleiferous,solubility and aqueous solubility,.,.,.,for instance,Thermal decomposition activation energy,From 200,downgrade to 40KJ/mol,From 125,downgrade to 50KJ/mol,From 140,downgrade to 50KJ/mol,In the redox system of aqueous solubility,inorganic,reducer,s,are usually used,and,a small amount of,organic reducers,such as alcohol,amine,and so on,are used too.,.,.,.,Systems of O,leiferous,Solubility are Often Used Initiators,tertiary amine，naphthenate，mercaptan，metallo organic compound,.,.,.,Example,benzoyl peroxide,and,N，Ndimethyl aniline initiating system,.,.,.,Some metallo organic compounds,Take trialkylboranel for example,it can react with the oxygen in the air,and form a redox initiation system,which can initiate olefinic monomers polymerization at a low temperature.,.,.,.,3.2.2,Decomposition Kinetics of Initiator,In each elementary reaction of radical polymerization,Initiation rate is the lowest one.,Have a strong effect on both overall polymerization rate and molecular weight.,Chain initiation rate,Controlled by the initiator decomposition rate.,By studying the initiator decomposition rate,we can find the,quantitative relationship between the radical generation rate and the initiator concentration,temperature,and time.,.,.,.,（,1,）,Thermal Decomposition Rate of Initiator,Initiator thermal decomposition is a,first order,reaction.,initiator,Primary radical,Decomposition rate of initiator,mol/(L,s),Rate constant for decomposition,s,-1,integrated,At a given temperature,，,through the plot of ln(I,/I,0,)to time t,Rate expression,.,.,.,（,1,）,Thermal Decomposition Rate of Initiator,the plot of ln(I,/I,0,)to t,Its,slope,=-k,d,ln(I,/I,0,),t/min,0.0,-0.4,-0.8,0.0,80,160,240,320,=(-0.4)-(-0.8)/(160-320)60,=-4.2x10,-5,(s,-1,),.,.,.,The halflife of the first order reaction-,t,1/2,To the first order reaction,we usually take the halflife to,characterize the,reaction rate.,Halflife is the time needed for the initiator to decompose to half its original,concentration,.,.,.,.,Arrhenius formulation,The dependence of the rate constant for initiator decomposition on temperature is in conformity to,Arrhenius formulation.,The plot of,lnk,d,to,1,/,T,should be a straight line.,Frequency,factor,-,A,d,can be worked out from the intercepting.,The decomposition free energy-,E,d,can be worked out from the slope.,.,.,.,Table 3-6 K,inetic Parameter of Some Typical Initiators,Initiators,solvent T/,o,C k,d,/S,-1,t,1/2,/h E,d,/kj/mol,AIBN 50 2.64*10,-6,73 128.4,60.5 1.16*10,-5,16.6,69.5 3.78*10,-5,5.1,BPO,benzene 60 2.0*10,-6,96 124.3,80 2.5*10,-5,7.7,cumine,hydroperoxide toluene 125 9*10,-6,21.4,139 3*10,-5,6.4,potassium,Persulphate 0.1mol/60 3.16*10,-6,61 140.2,L.KOH 70 2.33*10,-5,8.3,.,.,.,（,2,）Efficiency of Initiation,Only a part of primary radicals,are effective in initiating monomers polymerizing.,Some initiators are,exhausted,because of the,side reactions accompanying with the,induced decomposition,and/or the cage effect.,The efficiency of initiation is defined as the,ratio,of initiators which are used to initiate polymerization to initiators that decompose in the whole process of polymerization,and is denoted as f.,.,.,.,Induced Decomposition of Initiators,The,chain transfer reaction from free radicals to initiator molecules.,The total number of free radicals are not increased,however,one initiator is exhausted,which lowers the efficiency of initiation.,.,.,.,Factors Impact on the Efficiency of Initiation,The efficiency of initiation depends on the initiator type.,The induced decomposition of,AIBN is very little.,Hydroperoxide easily undergoes induced decomposition,which makes the efficiency of initiation lower than,0.5.,.,.,.,The type of monomers also affects the efficiency of initiation.,Monomers with high activity,such as,styrene,and acrylonitrile,can react with the free radicals rapidly,and reduce the induced decomposition.,In contrast
展开阅读全文