高分子化學(xué)浙江大學(xué)polymer3freeradicalcopolymerization

1、Chapter 3 Free Radical Copolymerization,2,1 Introduction,,Homopolymerization —— polymerization of one kind of monomer; Copolymerization (addition polymerization) —— polymerization of more than one kind

2、 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.,

3、4,Examples,StyreneStyrene + AcrylonitrileStyrene + ButadieneStyrene + Acrylonitrile+ Butadiene,PSSANSBRABS,Brittle, transparent, poor solvent tolerationHigh impact, good solvent tolerationHigh elasticity Enginee

4、ring plastics,Maleic anhydrideStyrene + maleic anhydride,No polymerSMA,,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

5、-propylene) 乙烯-丙烯無規(guī)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,-ABABBAABABBAAA

6、BABA-,Composition distributionthe relative amounts of each monomer unit incorporated into the copolymer, A% or B%,Sequence distributionthe way in which these monomer units are arranged within a polymer chain; AA or AB,

7、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 a

8、cetate %property 10 ~ 20 plastic 30 ~ 40adhesive 50 rubber,,10,Possible propagation sequences in free-radical copolymerization,11,assumptions in copolymerization,the rate of the prop

9、agation be chain-length-independent.only the terminal unit of the polymer radical can affect its reactivityno side reactions, such as depropagation, monomer partitioning, and various forms of complex formation,12,React

10、ions 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,

11、molar fraction of M2,2.1 Copolymer composition equation,,Steady-state assumption,,,,,,,Mayo-Lewis Equation,16,Reactivity ratio （競聚率）,Special cases: r1=0 and r2=0 Each comonomer prefers to react with the other. Perfe

12、ctly 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. Rand

13、om 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

14、 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 mechani

15、sm 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

16、the reactivity ratio as well.,20,,,,0,1,r1,r1>1 or k11>k12 tend to homo- than copolymn.,r1<1 or k11<k12 tend to co- than homopolymn.,r1= 0 or k11= 0only copolymn.,,,Variation of reactivity ratio,F is the fun

17、ction of both r and f,2.2 Copolymer composition curve,r1=? or k11>>k12 only homopolymn.,,butadiene r1 = 1.39, styrene r2 = 0.78,1. Ideal copolymerization (r1*r2=1),Typical copolymer composition curves,r1<1,r1>

18、;1,22,A. r1=r2=1,B. r11,C. r1>1, r2<1,azeotropic copolymerization恒比共聚copolymer composition equals to monomer feed,VDC (偏氯乙烯)- MMA, r1 = 1.0, r2 = 1.0Acrylamide(丙烯酰胺)-丙烯酸甘油酯, r1 = 1.0, r2 = 1.0 Ethylene-VAc

19、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 copolymer

20、ization (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 B

21、PO/AlR3,3. Others,Typical composition curves,r1<1 and r2 <1,r1>1 and r2 <1,r1>1 and r2 >1,block,r1 r2 = 1 random r1 = r2 = 0 alternative r1 1, r2 > 1 blo

22、ck or mixture of homopolymer r1 > 1, r2 < 1 close to random,Summery,27,Azeotropic composition恒比組成,Definition:,To get solution, it should be that r1 and r2>1 or r1 and r2<1,28,Independent on monom

23、er conversion,29,2.3 Copolymer composition with conversion,r1 1,,,f1orF1,conversion,,,r1 1,30,r1< 1，r2 < 1,,,f1orF1,,conversion,,,,r1>1，r2>1,,,,,,,31,Copolymer composition with conversion,Polymerized mo

24、nomer,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 integration,32,Average copolymer compos

25、ition,M0=1 M,St-MMAf10=0.8, f20=0.2,r1=0.53, r2=0.56,F1=f1=0.484,33,Controlling copolymer composition,苯乙烯-反丁烯二酸二乙酯共聚物瞬時組成與轉(zhuǎn)化率的關(guān)系(r1=0.30, r2=0.07),,,,,,,When the f10 is close to azeotropic point, the copolymer composit

26、ion slightly varies with conversion (<90%).When the f10 is far from azeotropic point, the copolymer composition greatly varies with conversion.,By adjusting feed ratio,Adding relatively active comonomer during polyme