Chapter 3 Free Radical Copolymerization,2,1 Introduction,Homopolymerization polymerization of one kind of monomer; Copolymerization (addition polymerization) polymerization of more than one kind of monomer;,1.1 Concept,New kinds of copolymer can be synthesized by copolymerization of different combination of various monomers. Copolymer generated from same monomers can have different compositions and topologies.,4,Examples,Styrene Styrene + Acrylonitrile Styrene + Butadiene Styrene + Acrylonitrile+ Butadiene,PS SAN SBR ABS,Brittle, transparent, poor solvent toleration High impact, good solvent toleration High elasticity Engineering plastics,Maleic anhydride Styrene + maleic anhydride,No polymer SMA,1.2 Type of copolymer,also obtained by other methods,Normally prepared by other methods,poly(ethylene-co-propylene) 乙烯-丙烯共聚物 poly(ethylene-r-propylene) 乙烯-丙烯无规共聚物 poly(ethylene-b-propylene) 乙烯-丙烯嵌段共聚物 poly(ethylene-g-propylene) 乙烯-丙烯接枝共聚物 poly(ethylene-a-styrene) 乙烯-苯乙烯交替共聚物,1.2 Nomenclature of copolymer,Key topics in copolymerization,-ABABBAABABBAAABABA-,Composition distribution the relative amounts of each monomer unit incorporated into the copolymer, A% or B%,Sequence distribution the way in which these monomer units are arranged within a polymer chain; AA or AB,8,2. Copolymer composition,9,Essential Point,The composition of a copolymer does not necessarily match the composition of the comonomers used in the reaction ( feed ratio 投料比).,Ethylene-vinyl acetate copolymer vinyl acetate % property 10 20 plastic 30 40 adhesive 50 rubber,10,Possible propagation sequences in free-radical copolymerization,11,assumptions in copolymerization,the rate of the propagation be chain-length-independent. only the terminal unit of the polymer radical can affect its reactivity no side reactions, such as depropagation, monomer partitioning, and various forms of complex formation,12,Reactions in copolymerization,13,The overall rates of consumption of monomers M1,M2 then follow these expressions:,ignore the initiation,The expression for instantaneous copolymer composition (F1/F2),molar fraction of M1,molar fraction of M2,2.1 Copolymer composition equation,Steady-state assumption,Mayo-Lewis Equation,16,Reactivity ratio （竞聚率）,Special cases: r1=0 and r2=0 Each comonomer prefers to react with the other. Perfectly alternating copolymer. r1 1 and r2 1 Each comonomer prefers to react with others of its own kind. Tendency to form block copolymers. r1 * r2=1 There is no preference due to the chain ends. Random incorporation of comonomers; “Ideal” copolymerization.,The ratio of rate coefficient of homopolymerization to copolymerization,17,Examples,Neither monomer homopolymerizes very well. Forms almost perfectly alternating copolymer of high MW. Alternating copolymerization is common in free radical reactions when one monomer has electron withdrawing groups and the other has electron donating groups.,18,Influnece of Polymerization mechanism on r,St(M1)-MMA(M2) Radical ： r1=0.52, r2=0.46; Cationic： r1=10, r2=0.1; Ionic: r1=0.1, r2=6;,19,Copolymer equation in terms of mole fraction,Copolymer composition depends on not only the monomer feed, but the reactivity ratio as well.,20,0,1,r1,r11 or k11k12 tend to homo- than copolymn.,r11 or k11k12 tend to co- than homopolymn.,r1= 0 or k11= 0 only copolymn.,Variation of reactivity ratio,F is the function of both r and f,2.2 Copolymer composition curve,r1= or k11k12 only homopolymn.,butadiene r1 = 1.39, styrene r2 = 0.78,1. Ideal copolymerization (r1*r2=1),Typical copolymer composition curves,r11,r11,22,A. r1=r2=1,B. r11,C. r11, r21,azeotropic copolymerization 恒比共聚 copolymer composition equals to monomer feed,VDC (偏氯乙烯)- MMA, r1 = 1.0, r2 = 1.0 Acrylamide(丙烯酰胺)-丙烯酸甘油酯, r1 = 1.0, r2 = 1.0 Ethylene-VAc r1 = 1.07, r2 = 1.08,23,Characteristics of ideal copolymerization,There is no preference due to the chain ends. Random incorporation of comonomers. “Ideal“ copolymerization,r1*r2=1,2. Alternative copolymerization (r1=r2=0),Typical composition curves,Each comonomer prefers to react with the other. Perfectly alternating copolymer. copolymer composition independent on monomer feed,If r2=0 and r1 0,St/MMA initiated by BPO/AlR3,3. Others,Typical composition curves,r11 and r2 1,r11 and r2 1,r11 and r2 1,block,r1 r2 = 1 random r1 = r2 = 0 alternative r1 1, r2 1 block or mixture of homopolymer r1 1, r2 1 close to random,Summery,27,Azeotropic composition 恒比组成,Definition:,To get solution, it should be that r1 and r21 or r1 and r21,28,Independent on monomer conversion,29,2.3 Copolymer composition with conversion,r1 1,f1 or F1,conversion,r1 1,30,r1 1，r2 1,f1 or F1,conversion,r11，r21,31,Copolymer composition with conversion,Polymerized monomer,Monomer before polym.,Monomer after polym.,Since f varies with conversion, F1 also varies with conversion. Therefore, the average copolymer composition should be obtained by integrat