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Chapter 5 Copolymerization

Chapter 5 Copolymerization. Part 2 Copolymer Composition. In the typical copolymerization, there are some interesting phenomena, such as, The difference between the monomer feed ratio to the product copolymer composition,

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Chapter 5 Copolymerization

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  1. Chapter 5 Copolymerization

  2. Part 2 Copolymer Composition • In the typical copolymerization, there are some interesting phenomena, such as, • The difference between the monomer feed ratio to the product copolymer composition, • Some monomer pairs are difficult to react with each other, while some monomers can react with other monomer but not react with itself. • That is because of the discrepancy of activity between different kinds of monomers.

  3. 5.2.1 Copolymer composition equation Chain polymerization • Initiation • Propagation • termination M1、M2:monomer pairs ~~M1*、~~M2*: reactive centers

  4. Chain initiation K i1 K i2

  5. Chain propagation

  6. Chain termination 2 k * * [ ] t 11 * = k M R M Polymer M + t 11 t 11 1 1 1 k * * * [ ] [ ] 12 * = k M M t R M Polymer M + t 2 12 t 1 12 2 1

  7. Assumptions for copolymerization • Activity equal theory: The reactivity of chain end is independent of chain length • Reactivity of a growing chain depends only on the terminal monomer unit • The most of monomers are consumed during the propagation and no depropagation

  8. Steady state of propagation:

  9. Deduction of copolymer composition

  10. The steady state assumptions on M1*、M2*

  11. definition

  12. Mayo-Lewis Equation In which, • d[M1]/d[M2]: instantaneous polymer composition • [M1]/[M2]： instantaneous monomer composition • r1、r2 ：reactivity ratio ~~M1*+M1→k11 r1 =k11/k12 ~~M2*+M2 → k22

  13. Another form of Mayo-Lewis Equation Definition: (5－18)

  14. Discussion of Mayo-Lewis Equation • Instantaneous copolymer composition • Normally copolymer composition is different from that of monomer pairs (feed ratio), except the case of r1=r2=1 or r1[M1]+[M2]=[M1]+r2 [M2]=1 • There are different kinds of active center, such as radical, anionic and cationic ion. The r1 and r2 of same monomer pairs should be different among different kinds of active center • For the ionic copolymerization, the reactivity ratio is greatly affected by the properties of anti-ion, solvent and temperature.

  15. 5.2.2 The copolymer composition curve and the type of copolymerization • Reactivity ratio R is the ratio between the activity of monomer pairs in the competed propagation. r1=K11/K12

  16. The relation between r1 and polymerization character • r1 = 0：only copolymerization but no homopolymerization； • 0 < r1 < 1： monomer tends to homopolymerization and the homopolymerization increase with the r decrease; • r1 = 1：same ability between homo- and copolymerization； • 1 < r1 < ： monomer tends to copolymerization and the copolymerization increase with the r increase;

  17. ③ ② ① ④

  18. Curve 1. Alternating copolymerization r1=0，r2=0 • e.g. 60℃，St(r1=0.01)—maleic anhydride(r2=0) F1～f1 plot

  19. character 1) Only copolymerization and no homopolymerization: k11=0, k22=0 2) Two kinds of monomer unit arrange alternatively，F1、F2 take half of chains 3) Practically it is r1→0 and r2→0 instead of r1=r2=0. Smaller r1*r2 is, stronger trends of alternative copolymerization shows.

  20. Curve 2. r1<1，r2<1，with azeotrope point Azeotrope point A r1=0.6 r2=0.3 R1=0.5 R2=0.5 F1～f1 plot

  21. At azeotrope point The azeotrope is important, particularly in industry, because the monomer and copolymer composition do not change with conversion, thus producing copolymers homogeneous in composition. Copolymerizations under the other conditions will change the instantaneous compositions along the composition curve.

  22. Curve 3. Ideal azeotrope copolymerization r1=0，r2=0 F1～f1 plot

  23. F1=f1 and do not change with conversion (ideal copolymerization) • k11= k12， k22 = k21，～～M1* and ～～M2* have same reactivity with M1 and M2； • e.g.： CF2=CF2～CF2＝CFCl St～p-MSt, 70℃

  24. Curve 4. r1 > 1，r2 < 1 or r1 < 1，r2 > 1 1) r1 > 1 (k11 > k12) and r2 < 1 (k22 < k21) shows that M1 is more active than M2 no matter for ～～M1* and ～～M2*. F1 is always larger than f1 and the curve is always above the diagonal. The situation is similar for r1 < 1，r2 > 1 and the curve is below the diagonal. 10 5 0.5 0.1

  25. 2） as r1 * r2 = 1 (r2=1/r1), it becomes ideal copolymerization In this case，～～M1* and ～～M2*，have the same preference for adding one or the other of two monomers reactivity.

  26. Curve 5. r1>1，r2>1 styrene(r1=1.38)/isoprene(r2=2.05)

  27. Character of curve 5 • The shape and position of curve 5 contrary to that of r1<1，r2<1; • There is azeotrope point • The monomer pairs prefer to homopolymerization rather than copolymerize. As r1 and r2 >> 1, the blocks form along the chain.

  28. 5.2.3 Integrated equation for copolymer composition The importance of composition control on product properties： SB rubber：S％ 22～25％ tyre S％↑ stiff tyre S％↓ cold resistant↑ 1）Composition is designed according to the final properties； 2）The composition of products are normally different from that of materials; 3）The copolymer composition change with the conversion. Key: how to prepare the copolymer with the expected composition.

  29. (1）The influence of conversion on the copolymer composition a. Qualitative description e.g.： F1～f1 curve (r1<1,r2<1) At point A (azeotrope) (f1)A=f1，F1＝(f1)A=f1 ; At point B, (F1)B decrease along the curve BO with conversion. At point C, it is contrary to that of point B.

  30. Conclusion：the copolymer composition change with conversion; the products are mixtures of copolymers with different composition (composition distribution) • F1～f1 curve (r1<1,r2<1)

  31. 2. Integrated equation • Skeist method: • For a binary system, total molar number of monomer pairs is M and F1>f1 • As dM of monomer are polymerized, the M1 unit in the copolymer chain increase F1dM and the monomer ratio change to f1-df1.

  32. Mf1 － (M-dM)(f1-df1) = F1dM ( 5-21 ) in which, Mf1－－the M1 in the material； F1dM－－the M1 unit in the copolymer f1-df1－－after dM of M1 reacted，the ratio of M1 in the material; (f1-df1)(M-dM)－－un reacted M1 in material.

  33. dM.df1 is neglected and then reset the above equation： Mdf1+f1dM=F1dM We got： Skeist Equation

  34. Definite the mole conversion

  35. ( 5-23a ) Meyer et. Al, ( 5-23b )

  36. With certain value of r1,r2 and initial feed ratio f01, we calculate the value of C,F1,and f1 The relation between average copolymer composition and conversion C, ( 5-24 )

  37. 1.0 f1 0.8 F1 average M1 in copolymer Mole fraction average M2 in copolymer F2 0.2 f2 0 1.0 conversion 1－M/M0

  38. 5.2.4 Copolymer composition distribution and control methods （1） Copolymer composition distribution A. In figure 5－4，st（r1=0.30）and diethyl fumarate（r2 = 0．07） • azeotrope

  39. Copolymerization of styrene and diethyl fumarate f1=0.80 f1=0.70 Azeotropic copolymer f1=0.57 f1=0.50 f1=0.40 f1=0.20

  40. Conclusion： 1. If the monomer feed ratio is azeotrope, the composition does not change with conversion; 2. If the monomer feed ratio is close to azeotrope, the composition does not change greatly; 3. If the monomer feed ratio is far from azeotrope, the composition will change greatly and no well-proportioned copolymer.

  41. (2) Copolymer composition control methods (1). one-pot method • As r1＜1，r2＜1 and the copolymer composition of target copolymer is close to that of the azeotropic copolymer, then the monomer pairs can be fed at one pot according to the target ratio. e.g.：As we want to prepare PSA with F1＝0.55，St(r1=0.41)/AN(r2=0.04), we can adopt one-pot method because F1’=0.62

  42. (2) Adding the high reactivity monomer method • Target：to keep f1 approach to f10 • method：A. half-batch adding B. continuous adding

  43. f10 (a) (b) f10 • r1<1,r2<1,F1>f1,M1 consumed quick，adding M1 • R1<1,r2<1,F1>f1,M2 consumed quick，adding M2

  44. F10 F10 f10 f10 (d) (c) c) r1>1,r2<1,normally adding M1，(F1>f1) d) r1<1,r2>1, normally adding M2，(F1<f1)

  45. (3). Control conversion method If F1～C curve has been got ahead (such as 5－4, r1=0.3, r2=0.07), the azeotrope (F1)A=(f1)A=0.57(horizontal line) • Curve 3：Since f10(=0.50) is close to (f1)A，F1 slightly changed with C. Before C％ reach to 80～90％，stop the reaction； • Curve 4：f10=0.60 and the situation is similar to 3； • Curve 1：Since f10(=0.20) is far from (f1)A，F1change greatly at small C％. The reaction should be kept at low conversion； • Curve 2：f10=0.80 and the situation is similar to 1. Normally we combined both method 2 and 3！

  46. Part 2 Copolymer Composition • In the typical copolymerization, there are some interesting phenomena, such as, • The difference between the monomer feed ratio to the product copolymer composition, • Some monomer pairs are difficult to react with each other, while some monomers can react with other monomer but not react with itself. • That is because of the discrepancy of activity between different kinds of monomers.

  47. 5.2.1 Copolymer composition equation Chain polymerization • Initiation • Propagation • termination M1、M2:monomer pairs ~~M1*、~~M2*: reactive centers

  48. Chain initiation K i1 K i2

  49. Chain propagation

  50. Chain termination 2 k * * [ ] t 11 * = k M R M Polymer M + t 11 t 11 1 1 1 k * * * [ ] [ ] 12 * = k M M t R M Polymer M + t 2 12 t 1 12 2 1

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