1. 6.2 Overview Cationic Anionic Coordination
According to the sorts of the active center at the end of long chain, ionic polymeriza-tion can be classified into three categories:
Cationic
Anionic
Coordination

2. （1）The active center of cationic polymerization is a
carbocation:
（2）The active center of anionic polymerization is a
carboanion

3. （3）The active center of coordination poly-
merization is coordinated ion with a
metallic carbon bond.

4. Feature and Industrial value of Ionic Polymerization
The mechanism and dynamics of the ionic polymerization is comparatively complex. There are various influencing factors, for instance, the monomer, the ionic initiator, the polarity and solvating power of the solvent and the temperature which influenced prominently. The study of this category is incomplete.

5. However, some essential polymers, like butyl rubber, polyisoprene, polyoxymethylene, could only be synthesized by ionic polymerization. Some other monomers, such as ethylene, propylene, butadiene and styrene have unique structures and properties and special industrial value when they are polymerized by ionic polymerization or coordinated ionic polymer-ization.

6. Ring-Opening polymerization
Ring-Opening polymerization is defined as the process in which the ring of monomer opens, and a linear polymer forms. The general formula is:
Hetero atom or functional group in ring monomer杂原子或环单体的官能团
Like O,N,S, -CH=CH- , -CONH-, -COO-,.etc.
With groups like ether,ester, amide, imine and double bond etc.

7. Ring-Opening polymerization could also be used to synthesize polymer from monomer
For example, polyamine can be prepared from caprolactam(己内酰胺), and polyformaldehyde,which is used as a engineering plastics, can be produced from trioxymethylene（三聚甲醛）.

8. Development of Ring-Opening Polymerization
Ring-Opening polymerization has been developed and studied since 1950s. A lot of products which have been industrialized, such as, poly-caprolactam, polyformaldehyde, polytetrahydrofuran, polyethylene oxide, polypropylene oxide etc. As the late direction, isomerized ring-opening polymerization of cycloolefin and spirocyclic monomer have been studied.异构化开环环烯烃和螺环单体的聚合进行了研究。
聚己内酰胺，聚甲醛，聚四氢呋喃，氧化聚乙烯，氧化聚丙烯等

9. Controlled Polymerization
Controlled Polymerization is the new direction of the late 20 years.

10. Controlled Polymerization
For the late 20 years, polymer synthesis chemistry has been developed remarkably in the new monomer, initiator, catalyst, synthesis method and polymerization technology. The employment of polymer material is elevated in both quality and quantity.
The output of current polymer material expands.

11. Functional and fine polymer materials appears;
Designing synthesis concept and controlled polymerization technology are studied to control the size, figure, constitute, and chemical and geometrical structure of the polymer.

12. 6.3 Cationic Polymerization
The First cationic polymerization, in which styrene is polymerized with tin tetrachloride, was not realized as it, for there was no polymer concept then.
Vinyl ether is polymerized by acid or metal halide.
Whitemere firstly brought in concept of cationic polymerization by study of polymerization of alkene with strong acid as catalyst, in which a low-molecule-weight polymer was produced.

13. The cationic polymerization of isobutylene（异丁烯） was studied to bring out the mechanism of polymerization and to indicate the effects, to polymerization rate and molecular weight, of some factors, like temperature, solvent, catalyst, cocatalyst. This study elevated the industrial produce of butyl rubber.

14. 6.3.1 Initiator and Monomer
Alkenes with electron-donating substituents are cationic polymerizable.
Isobutylene (1) 1,3-butadiene (2) vinyl ether (3)
styrene(4)1-methyl styrene(5)methyl aldehyde(6)

15. The typical substances are listed in table 6-3-1
A Cationic catalyst or initiator could react with the above-mentioned monomer to produce a carbocationic active center.
The cationic initiators can be classified into two categories:
strong proton acid
Lewis acid
The typical substances are listed in table 6-3-1

16. Table 6-3-1 Cationic Initiator
Initiator Typical Substances
1．Strong proton acid H2SO4, HClO4, H3PO4,
Cl3COOH…
2．Lewis Acid BF3 , BF3O(C2H5)2,
BCl3, TiCl4, TiBr4 ,
AlCl3 , SnCl4

17. The Initiator and Coinitiator of a Lewis acid
A Lewis acid initiator can only be affecting with water, methanol, even hydrochloric ether acting as a coinitiator. 卤代烃
To cut the side reaction，cationic polymerization
almost take place under low temperature，and the
solvent must be inert and very dry.

18. 6.3.2 Cationic Polymerization Mechanism
Cationic polymerization belonging in chain polymerization，contains:
Initiation,
Propagation,
Transfer,
Termination.

19. (1) Initiation Consists of two steps:
Firstly，the initiator reacts to produce a proton or carbocation;
Then the carbocation adds to the monomer to produce a monomer carbocation.
Strong proton acids dissociate into protons in water-free medium（非水介质中）.

20. dissociation

21. (1) Initiation
A Lewis acid initiator firstly react with a co-initiator, and then dissociate into a proton. The process is shown as the following reaction equation.

22. The proton adds onto a monomer to produce a monomer carbocation.
The addition of a initiator molecule to the monomer essentially is the addition of a initiator ion pair to a double bond.

23. (2) Propagation
The monomer inserts into the ion pair and then add to the carbocation to form a carbon-carbon single bond. The propagation goes along repeatedly and continuously to produce a long-chain polymer.

24. (2) Propagation
The mechanism of the cationic propagation seems almost as the same as radical chain propagation, but in fact the cationic propagation is very complex. An active center is greatly influenced by the dissociation degree of the ion pair. With the different mediums or solvents, the active center could exist in different forms as follows:

25. (2) Propagation Free ion Loose ion pair Covalent bond
Intimate ion pair

26. Isomerization Polymerization
For the difference in the stability of the carbocation, the polymerization often accompany with isomerization, for instance, the isomerization polymerization of β-pinene(β-蒎烯).

27. CH3
-[-CH2—C6H8—C--]n—

28. Isomerization Polymerization
Generally a tertiary cation is more stable than a secondary cation, and a primary cation which has the lowest stability. So isomerization often occurs in polymerizng process when a primary and secondary cation are apt to be transformed to a tertiary cation.

29. （3）Transfer
Under high temperature，the chain transfer can be found evidently.
The chain transfers to a monomer：

30. （3）Transfer
The chain transfers to a gegenion：

31. （4）Termination
1. Combination with gegenion，for example:

32. （4）Termination
2. The add-terminating-agent termination is to terminate cationic polymerization by adding protonizing agent like water, alcohol and amine etc. The excess amount of the terminator was stabilized by solvating around the proton so that can`t initiate the polymerization to terminate the reaction any more.

34. The feature of the cationic polymerization is fast initiation, rapid propagation, very extremely easy transfer and comparatively hard to ter-mination, in which a terminator is often indispensable(必要的).

35. 6.3.3 Kinetic (1) The rate equation
Conveniently，the following general equations can be used to show elementary reactions of the cationic polymerization，where:
C- Initiator（C-Lewis酸）
RX-coinitiator
M-monomer
(2) The degree of polymerization

36. (1) The Rate equation
Initiation

37. (1) The rate equation
Propagation

38. (1) The rate equation
Chain Transfer
Termination
自发终止，再生出引发剂—共引发剂络合物

39. (1) The rate equation
The above-mentioned reaction equations merely show the ionic polymerization with a ion pair as an active center. Actually the polymerization also have other kinds of active centers, for instance,free cations which are completely dissociated。
The polymerization rate differs with different active centers.

40. The rate equation of the polymerization with an ion-pair active center
The rate equation of the polymerization with an ion-pair active center can be expressed as：
The termination is a first order reaction. Its rate is directly proportional to the active chain concentration in propagation
[M]
(6－1)
(6－2)

41. Treated with stable-states, Ri = Rt, so
The rate equation of the polymerization with an ion pair as a model is:
(6－3)
(6－4)

42. （1）The rate equation
The polymerization with a free ion as a model has a similar expression.
The values of kinetic rate constant kp and kt prominently differ with different models.

43. （1）The rate Equation
The expression of the chain initiating rate Ri is complicated. Given a fixed temperature and a solvent, initiating rate depends on not only the reaction center, the ion pair or free ion, but also the reaction equilibrium of the catalyst and cocatalyst.
Generally the expression of Ri can be written as:
(6－5)

44. (1) The rate Equation
For each type of the polymerization system,（C，RX，M）appear different Ri expressions. For example, the Ri of the polymerizing system of styrene with SnC14 as catalyst can be expressed as:
(6－6)
According to the following equation:

45. (1) The rate Equation
(6－7)
(6－8)
(6－9)

46. (2) The Degree of the Polymerization(DP)
Similarly to the free radical polymerization，the average DP equals the ratio of the monomer-expending rate to the polymer-creating rate.
The polymer producing reaction contains termination and transfer, So that:
(6－10)

47. (2) DP The rate equation of the chain transfer （6－11）
Substituting it into (6－10), the expression of DP
is（6—12）

48. (2) DP Its reciprocal form is more commonly applied,
(6－12)
Its reciprocal form is more commonly applied,
and ktrM / kp is substituted by the chain transfer
constant:
(6－13)

49. (2) DP
The above expression only deals with the chain transfer to the monomer. Involving transfer to the solvent, the expression has one more term: +
(6－14)

50. (2) DP
In the cationic polymerization the polymer is mainly gained by transfer, and is different from the polymer in the radical polymerization that is gained by termination.
Without any impurity or solvent chain transfer, DP mainly depends on equation（6－13）.
The monomer-ward chain transfer constant CM , which is the second term in the right of the equation, is independent of the concentration of monomer.

51. Actually, no matter how the operation is strict, there is trace quantitative impurity in the polymerizing system. For example, trace quantitative vapour water cause a large value of Cs. When [S], the quantity of impurity, increases, DP drops obviously.

52. (3) Influence of Temperature
The initiating rate depends on the producing rate of ion pairs (free ions). The activation energy of the dissociating equilibrium reaction is very low, so the cationic initiating rate is lightly dependent of the temperature.

54. The Effect of the Temperature on the Polymerization Rate
The cationic polymerization----The activation energy of initiation is very low，and the activation energy of the termination is higher than that of the propagation. The total activation energy of the polymerization E＝Ep+Ei-Et , and is negative.

55. The cationic polymerization rate generally drops when the temperature increases. This case is opposite to that of the radical polymerization. This is because that the radical polymerization has very high chain initiating activation energy, making the total polymer-izing activation energy positive.

56. The Effect of the Temperature on DP
The effect of the temperature on DP or MW could be estimated by the DP activation energy.
The DP activation energy of the cationic polymerization E is almost negative, because the Ep is somewhat low. No matter the termination or monomer transfer leadingly produces, the polymer producing activation energy Et or EtrM is higher than Ep，
DP always increases when the polymerization temperature falls.

57. (4) Influence of solvent and gegenion
In the ionic polymerization, there are gegenions around the active center. The combination among the gegenions and medium, which could be covalent, ion pairs, even free ions, changes when the properties of them are different.
The center of the ion polymerization is mostly ion pairs or free ions in the equilibrium state。

58. (4) Influence of Solvent and Gegenion
kp(the apparent propagating rate constant) measured by experiment, is the contribution sum of the propagating rate constant of ions pair and free ion.
kp=(1-α)k(±) +αk(+) (6－17)
α is the degree of dissociation from ion pairs to free ions

59. The propagating rate constant of free ion, k(+), is 1~6 order of magnitudes larger than that of ion pairs, k(±).

60. (4）Influence of Solvent and Gegenion
With the different properties of solvents（polarity or solvating power）, the state of combination among ions differs, which changing the relative concentrations of the ion pair and the free ion. The higher polarity and solvating power is，the more proportion of incompact pairs take in free ions and ion pairs. As a result, the polymerization rate and DP increases.

61. Solvent Dielectric Constant Kp/25℃,l/mol.s
Table 6-4 The Effect of Solvent on the Cationic Polymerization of Styrene（HClO4 as a initiator）
Solvent Dielectric Constant Kp/25℃,l/mol.s
CCl
CCl4/(CH2Cl)2,40/
CCl4/(CH2Cl)2,20/
(CH2Cl)

62. (4）Influence of the Solvent and Gegenion
Solvents with high polarity are favorable to the chain propagation and could accelerate the polymerizing process, but as a polymerization solvent, the reagent is required to be inert to the center ion, and should be able to dissolve polymer under low temperature and keep fluid. So some solvents with low polarity , like alkyl halide, are chosen,while some oxygenous reagents, like THF, are out of choice.

63. (4) Influence of Solvent and Gegenion
The nucleophilicity of gegenion strongly affects the polymerization. Too-strong- nucleophilicity gegeion could combine with cations to terminate the chain.
The volume of the gegenion also greatly affects the polymerization rate. The more volume of the gegenion is, the more relax the ion pair is, and the higher the polymerization rate is.
For example: Polymerizing styrene in 1,2-dichloroethane under 25℃, with I2, SnCl4--H2O and HCIO4 as initiator, respectively the apparent propagating rate constants are 0.003, 0.42 and 1.70 L/mol.s.

64. (4) Influence of the Solvent and Gegenion
To compare the features of the cationic polymerization and radical polymer-ization, the separate kinetic data of the polymerization of vinyl monomer, with H2SO4 as a initiator, are chosen.

65. Thus it can be seen that the kp of the cationic poly-merization is not higher than that of radical polymer-ization. However because the kt of the cationic poly-merization is low, the kp/kt1/2 of the cationic polymer-ization is much higher than that of the radical polymer-ization, and the concentration of center is high, the rate of the cationic polymerization is much higher than that of the radical polymerization.

66. 6.3.6 Brief Summary of the Cationic Polymerization
1.Monomer and Initiator
Monomer:
Push-electron group, the activity of M depends
on the push-election ability of substitute.
Initiator:
Proton acids or Lewis acids, the substances which supply protons or carbo-cations.

67. Requirement: of which the ability to supply protons or carbocations is strong and the gegenion nucleophilicity is weak.
亲核性

68. 2. Mechanism
Initiation: Ei = KJ/mol
Propagation: more complicated than the
radical polymerization
Carbocation being apt to isomerize
碳正离子易重排

69. Transfer: mainly to monomer, solvent and gegenion
Cationic polymerization is apt to transfer, and its CM is larger than that of the radical polymerization.
Termination: single-group termination, mainly to
the monomer reaction.
Summary: fast initiation, rapid propagation, greatly easy transfer and comparatively hard termination.

70. 3. Kinetics
a. Rp:
(6-9) b.
(6-10)

71. E ＝Ep - Et or E ＝Ep – EtrM<0:
C. Temperature
The temperature elevated , polymerization reduces.
ER＝Ep - Et <0:
E ＝Ep - Et or E ＝Ep – EtrM<0:
The temperature elevated , polymerization reduces.

72. d. The effect of the solvent and gegenion
When Solvent polarity increases, the incompact ion pairs multiply, and the polymerization rate enhances.
The gegenion with nucleophilicity, polymerization
rate reduces; the volume of gegenion enhances,
the incompact ion pairs multiply and the poly-
merization rate increases.