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Ionic, Ring-Opening, & Controlled Polymerization. Chapter 4. 4.3 Anionic Polymerization. 4.3.1 Initiator and Monomer 4.3.2 Mechanism 4.3.3 Living Polymer 4.3.4 Kinetics 4.3.5 Comparison between Radical & Ionic Polymerization. Overview.

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slide2

4.3 Anionic Polymerization

4.3.1 Initiator and Monomer

4.3.2 Mechanism

4.3.3 Living Polymer

4.3.4 Kinetics

4.3.5 Comparison between Radical & Ionic

Polymerization

overview
Overview
  • 1877 ---- Waitz ring-openingly polymerized

ethylene oxide.

  • 1949 --- Styrene and acrylic nitrile are polymerized in

liquid ammonia with potassium amide as a

initiator, which bring out a mechanism of the

anionic polymerization.

  • 1952---- Quantitative kinetic studies were done.
  • 1956 ---- Szwarc notified the cationic living polymer-

ization.

slide4
Polymers of specific structure, like ABA block copolymer, starshaped polymer and pectinate polymer, could be synthesized, meeting the aim ofpolymer molecular design.Industrial practice is realized, for example, the produce of liquid butadiene styrene rubber and butadiene styrene block copolymer SBS resin has been industrialized.
slide5

4·3·1 The Initiator and Monomer

  • Typical anionic polymerizable monomers : styrene, MMA and acrylic nitrile etc.
  • All types of monomers are π-π conjugated system or that with electron attracting group, makeing the density of electron cloud ofdouble bond decline.
  • The anionic active center reacts with double bond by addition reaction.

Anionic polymerizable initiators are listed in the following table.

slide6

Common Intiator

Type of Initiator Molecular Formula or Examples

alkali metals suspension system Na suspends in THF or fluid chlorin

organic radical anion naphthalene natriuminitiator

alkyl or aryl lithium reagent n-C4H9Li

Grignard eagent RMgX( R-alkyl or aryl group)

alkyl aluminium AlR3

4 3 1 the initiator and monomer
4·3·1 The Initiator and Monomer

In these initiators:

  • The alkali metals suspension system is that in which melted alkali metal tiny beads disperse in an inert organic solvent;
  • Organic lithium reagent is prepared by metal lithium and alkyl halide in an organic solvent;
  • Grignard reagent is prepared by the reaction of metal Mg and alkyl halide.
4 3 1 the initiator and monomer1
4·3·1 The Initiator and Monomer
  • The Radical anionic initiator,for example, naphthalene natrium must be prepared in an ether solvent by the reaction of natrium mirror and naphthalene.
slide9

The occurrence of bottle green solution indicates the produce of radical anionic initiator.

Water or wet air must be strictly removed, or the activity of initiator will be destroyed.

4 3 1 the initiator and monomer2
4·3·1 The Initiator and Monomer
  • Aluminium alkyl is apt to burn in the air.
  • Removing the solvent from lithium alkyl and Grignard reagent, the residual solid is inclined to be blasted.

So these anionic polymerization initiators are used

in the form of a solution, in which inert organic solvents are chosen.

4 3 1 the initiator and monomer3
4·3·1 The Initiator and Monomer

In many anionic polymerizations, the length of the chain depends on the quantity of the initiator. In principle, every initiator molecular produce a polymer chain. So the more the quantity of the initiator adds,the lower the MW of produced polymer is. The Polymer of narrow MWD could be prepared by this kind of polymerization.

4 3 2 mechanism
4.3.2 Mechanism

The Anionic polymerization still belongs to the chain polymerization. It consists of 3 elementary reactions:

  • Initiation
  • Propagation
  • Termination
1 initiation
(1)Initiation

The initiating progress is that the initiator is added to the monomer double bond to produce an anionic monomer active center:

In the above equation, M represent metal,and Y group is an

Electron attracting group, which is apt to be attacked by the car-

boanion of the initiator.

1 initiation1
(1)Initiation

an Initiator molecule is often in the state of association in the solution. For example:

(LiC4H9)4 4 LiC4H9Li+/C4H9-

  • Before the initiation,the tetramer must dissociate to produce positive and negative ion pairs.
slide15

Carboanion is greatly instable and have very

high reaction activity with the monomer double

bond carbon atom, of which the electron

cloud density is brought low by the influence

of Y.

  • Gegenion, being an ion pair, is always around

the active center at the chain end.

2 propagation
(2)Propagation

The chain propagation is that the monomer continuously inserts the ion pairs and adds to the anion at the chain. This progress carries along until the monomer is used up or the chain termination occurs.

2 propagation1
(2)Propagation

1.Reaction active centers are of different types,

like intimate ion pairs, loose ion pairs, free

ion, so that the corresponding propagation

reaction activities are greatly different.

2. In the solvents of different polarities, the

relative contentof each type of the active center

differs, which affects the total propagation reaction rate.

slide18

In the solvent of strong polarity or solvating power, the content of the incompact or free ion and the propagation reaction rate is high.

2 propagation2
(2)Propagation

3.The volume and negativity of the gegenion

also affect chain propagation.

The less the volume of the gegenion is, the stronger its electrophilicity is.

In the solvent of low polarity there are more compact ion pairs.

slide20

In the solvent of high polarity, for the higher solvated power, more incompact ion pairs gain.

The effect of the gegenion is very complicated。

3 transfer
(3) Transfer

The chain transfer occurs less in anionic polymerization, especially under low temperature.

the reason for the hardness of termin ation in anionic polymerization
The reason for the hardness of termin-

ation in anionic polymerization

3 transfer and termination
(3) Transfer and Termination
  • An Active center is similarly carboanion, where double-group termination cannot occur.
  • A Gegenion is a metal ion, not radical;
  • Carboanion is hard to take the chain transfer with its self-generating M.
4 termination1
(4)Termination
  • In case the terminator in the reaction system is removed completely, the activity of the living chain end can remain until all monomers are used up.
  • When new monomers added, the polymerization can restart. This is so-called living polymerization。
  • But in fact the activity can remain only a few days, for a trace amount of proton impurity is difficult to avoid, for example, the Si一OH group on the surface of glass is also a kind of the terminator.
4 termination2
(4)Termination

Some kinds of end groups gradually loses activity in isomerization, for example, the Isomerizatin of the styrene anion in THF solvent.

4 3 3 the living polymer
4.3.3 The Living Polymer
  • As long as no termination occurs, though all monomers are used up, the polymer still remain activity. Whwn new monomer added, the polymer-ization restart. When another kind of monomers added, a block polymer produces.
  • Many initiator can be used in the living polymerization. The most convenient is metal Na and naphthalene natrium initiator.
slide28
Alkali metal Na transfers the electron of the outer layer to the monomer, to form a monomer anion radical, which is produced, through the radical double-group termination, double anion to take on the living polymerization.
4 3 3 the living polymer2
4.3.3 The Living Polymer

The polymerization of butadiene initiated by metal Na, in which buna rubber gains, is one of the living polymerizations. Naphthalene natrium initiator transfer electrons to the monomer to produce double anions. The polymerization propagates in both sides of molecule as the following equation:

4 3 3 the living polymer3
4.3.3 The Living Polymer

(1)The initiation is very fast, in which all the initiators

immediately join in the initiating progress and

are transferred to active centers.

The feature of the living polymerization is that the MWD of product is quite narrow.

The reasons are:

(2)All chains propagates at the same rate until monomers are used up. Every active chain has the same chance to share all of the monomers. The MW of the product is nearly similar.

slide32

(3)No chain transfer and chain termination.

(4)Depolymerization can be overlooked.

4 3 3 the application of the living polymerization
4.3.3 The application of the Living Polymerization
  • To synthesis a monodisperse polymer;
  • To measure the anionic polymerization rate constant;
  • To prepare a block polymer;
  • To prepare a telechelic polymer.
4 3 4 kinetics
4.3.4 Kinetics

Anionic initiator nearly quantitatively and immediately dissociate into positive and negative ions which have initiation activity. All of the carboanions are added to monomers at once, and at the same time the propagation starts:

4 3 4 kinetics1
4.3.4 Kinetics

According to the solvating power of the solvent and the character of the gegenion, the active center could be a free ion or an ion pair. Ion pairs differ in compact degree of dissociation. Mostly several kinds of active centers exist proportionally.

Compactly only the primary form is considered, for example, the free ion, so the propagation can be written as:

4 3 4 kinetics3
4.3.4 Kinetics
  • Suppose that a cation is always next to an anion, there is no chain terminator, and the polymerization progresses with no chain transfer and under low temperature, a living polymerization occurs.
  • The reaction kinetics, which is quite easy to know, is that during the polymerization no new initiation and termination occurs. That is to say that the concentration of the active center keeps no change.
  • The concentration of the active center indicates the total concentration of all active centers produced by initiator at the beginning of the polymerization.
1 the polymerization rate equation
(1)The Polymerization Rate Equation

The total polymerization rate equation is the propagation reaction rate equation(4-18)

Constant

(4-18)

The total concentration of all chain active centers

=

The concentration of the added

initiators [R-G]0

1 the polymerization rate equation1
(1)The Polymerization Rate Equation

So,

(4-19)

Integrating this equation, the change of monomer

concentration with varied time results.

It`s a first order reaction.

(4-20)

2 the average kinetic chain length
(2)The Average Kinetic Chain Length

In the living polymerization,for there is no chain termination, the kinetic chain propagation will not stop until monomers are used up.

The average kinetic chain length is defined as:

(4-21)

(4-22)

2 the average kinetic chain length1
(2)The average Kinetic Chain Length

When t goes infinite, that is to say the monomers are used up, the longest kinetic chain length is:

(4-23)

3 average dp
(3) Average DP

Average DP is the number of monomers consumed by each polymer molecule. If every active center forms one polymer molecule, then:

(4-24)

3 average dp1
(3) Average DP

Taking naphthalene natrium or metal Na as the initiator, the polymerization is called double anion propagation polymerization, in which one polymer molecule has two active centers and consume two initiator molecule. So,

(4-25)

3 average dp2
(3) Average DP

The MW of this kind of polymer obeys Poisson distribution. Mol fraction of its x-polymer, nx, is:

(4-26)

4 factors influencing the chain propagation rate constant
(4)Factors Influencing the Chain Propagation Rate Constant
  • If all initiators can quantitatively dissociate into positive and negative ions before chain propagation and no chain termination occurs, then according to kinetic equations
  • (4-19)and(4-20), the polymerization rate Rp,

can be determined, or the rate constant kp can be

directly determined by the monomer transfer ratio.

4 factors influencing the chain propagation rate constant1
(4)Factors Influencing the Chain Propagation Rate Constant
  • The active center of chain propagation can be free anions, ion pairs or the mixture of both.
  • Found by experiment, kp is affected by the solvent and the property of gegenion.
  • If there is only one kind of the active center, free anions, the solvent and the type of gegenion isn’t effective.
  • So the form of the active center is mainly or totally ion pairs.
4 factors influencing the chain propagation rate constant2
(4)Factors Influencing the Chain Propagation Rate Constant

In principle during the polymerization progress the equilibrium between ion pairs and free ions always exists:

slide48

Diluted by a solvent, that is to say, the concentration of [R-G]0 reduces,the dissocia-tion equilibrium moves rightward. Extrapolating the experimental value of kp to the direction of solution infinite dilution, the chain propagation rate constant of the free ion, k-, gains. It proved experimentally that the k-value of the free ion is much larger than that of the ion pair.

4 factors influencing chain propagation rate constant
(4)Factors Influencing Chain Propagation Rate Constant

Polarity and solvating of the solvent affect the dissociation degree of the ion pair. So the comprehensive value of the apparent propagation rate constant kp must be affected, too.

Table 4-6 shows the effect of the solvent on kp of styrene anionic polymerization.

table 4 6 effect of the solvent to k p of styrene anionic polymerization
Table 4-6 Effect of the Solvent to kp of Styrene Anionic Polymerization*

Solvent dielectric constant /D Kp/ (L/mol.s)

benzene 2.2 2

1,4-dioxy hexatomic ring 2.2 5

THF 7.6 550

1,2-dimethoxy ethane 5.5 3800

※Determined in styrene polymerization initiated

by naphthalene natrium under 25℃.

4 factors influencing the chain propagation rate constant3
(4)Factors Influencing the Chain Propagation Rate Constant
  • The property and solvated power of gegenion

also affect the dissociation degree of the ion

pair, so as to affect value of the propagation

rate constant of the ion pair.

slide52
The effect of the temperature, which varies with different solvents and polymerization systems, can only be determined by experiment.
4 factors influencing the chain propagation rate constant4
(4)Factors Influencing the Chain Propagation Rate Constant

On the whole,polymerization feature is mainly determined by chain propagation, of which the activation energy is very low, and varies little with the change of the temperature.

But dissociation equilibrium of the ion pair, the solvating power, and even the side reaction are affected, where a current rule is hard to be summed up.

Without chain transfer and termination, polymer MW is not easily affected by the temperature.

5 association phenomenon of alkyl lithium
(5)Association Phenomenon of Alkyl Lithium
  • Alkyl lithium, for example, butyl lithium is a kind of the initiator used commonly in the anionic polymerization.
  • In the nonpolarity solvent, like benzene, methylbenzene, hexyl- hydride and cyclohexane, there is dissociation phenomenon, which makes effective initiator concentration reduced. As a result, polymerization rate obviously lowers.
slide55
Fox example:

Styrene polymerization in benzene solvent initiated by butyl lithium is several orders of magnitude lower than that by naphthalene natrium.

5 association phenomenon of alkyl lithium1
(5)Association Phenomenon of Alkyl Lithium
  • When the concentration of the initiator is very low( lower than 10-4~10-5), the association of ortho butyl lithium occurs litter. Both the initiation rate and the propagation rate are proportional to the concentration of ortho butyl lithium.
  • When the concentration of the initiator increase, Ri and RP are directly proportional to the sixth root and square root of the concentration of ortho butyl lithium,respectively.
slide57
The dissociation phenomenon also exists in other kind of alkyl lithium initiator, but dissociation number is not always same.

For example:

Dissociation number of butyl lithium could be 6, and that of secondary and tertiary butyl lithium are 4.

5 association phenomenon of alkyl lithium2
(5)Association Phenomenon of Alkyl Lithium
  • All of the above association phenomenan, besides disappear in a highly dilute solution, completely disappear in a polar solvent, for example, THF. The Polymerization rate is greatly enhanced. Adding polybasic amine,for example, N,N,N’,N’—tetramethylethylene diamine (TMEDA), polyether, which is a comparatively strong complexing agent, can destroy the association of alkyl lithium, too.

Elevating polymerization temperature can also weaken association.

4 3 6 brief summary of the cationic polymerization
4.3.6 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 (coinitiators)

the substances which supply protons or carbo-

cations

slide60

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

4 3 6 brief summary of the cationic polymerization1
4.3.6 Brief Summary of the Cationic Polymerization

2. Mechanism

Initiation: Ei = 8.4 --21 KJ/mol

Propagation: more complicated than the

radical polymerization

a) Diversiform spike;

b) Carbocation being apt to isomerize

4 3 6 brief summary of the cationic polymerization2
4.3.6 Brief Summary of the Cationic Polymerization

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 gegenion reaction

Summary: fast initiation, rapid propagation, greatly easy transfer and comparatively hard termination

4 3 6 brief summary of cationic polymerization1
4.3.6 Brief Summary of Cationic Polymerization

C. Temperature

The temperature elevated , polymerization reduces.

ER=Ep - Et<0:

E =Ep - Et or E =Ep – EtrM<0:

The temperature elevated , polymerization reduces.

4 3 6 brief summary of the cationic polymerization3
4.3.6 Brief Summary of the Cationic Polymerization

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.

4 3 6 brief summary of the cationic polymerization4
4.3.6 Brief Summary of the Cationic Polymerization

1. Monomer and initiator

Monomer: With electron attracting groups, the

activity of M depends on the

electron attracting ability of the

substituent

Initiator: an alkal reagent

4 3 6 brief summary of the cationic polymerization5
4.3.6 Brief Summary of the cationic Polymerization

2. Mechanism

Transfer and termination: no transfer,

no termination-------living polymerization

Initiation: The initiators instantaneously and

quantitatively produce spikes.

Single anion spikes and double anion spikes

Propagation: the form of spikes is diverse

4 3 6 brief summary of the cationic polymerization6
4.3.6 Brief Summary of the Cationic Polymerization
  • Living Polymer

1) definition

2) applications

slide69

4.3.6 Brief Summary of the Cationic

Polymerization

3. Kinetics

a. Rp:

4 3 6 brief summary of the cationic polymerization9
4.3.6 Brief Summary of the cationic Polymerization

The property of solvent

The solvalrility increases with increase of the solvent between polarity, increasing the distance between ion pairs, the amount of loose ion pairs, the concentration of the free ion and hence the rate of polymerization.

4 3 6 comparison between the radical polymerization and the ionic poly merization
4.3.6 Comparison between the radical polymerization and the ionic poly- merization

(1)the type of the initiator

(2)the monomer structure

(3)the effect of the solvent

(4)the polymerization temperature

(5)the polymerization mechanism

4 3 6 comparison between radical polymerization and ionic polymerization
4.3.6 Comparison between radical polymerization and ionic polymerization

(1)the type of the initiator

  • Radical polymerization usually uses reagents easy to thermally decompose into a peroxidate , or azo compound as the initiator. The property of initiator merely affects the process of initiation.
  • Ionic polymerization uses reagents apt to produce active ions as the initiator.
4 3 6 comparison between radical polymerization and ionic polymerization1
4.3.6 Comparison between radical polymerization and ionic polymerization

(1)the type of the initiator

  • A cationic initiator is an electrophilic reagent , mainly Lewis acid;
  • An anionic initiator is a nucleophilic reagent , mainly alkali metals and their organic compounds;
slide76
Because a gegenion always exists around the active center, the property of an ionic initiator affects not only the elementary reaction of initiation, but also the propagation and termination;
  • Gegenion affects polymerization all the way.
4 3 6 comparison between radical polymerization and ionic polymerization2
4.3.6 Comparison between radical polymerization and ionic polymerization

(2)The Monomer Structure

The ionic polymerization have high selectivity of the monomer.

  • Vinyl monomers with push-electron groups, of which the density of electron cloud on double bond increases, are apt to the cationic polymerization.
  • Vinyl monomers with attract-electron groups are apt to the anionic polymerization.
  • Vinyl monomers with weak attract-electron groups are apt to the radical polymerization.
4 3 6 comparison between radical polymerization and ionic polymerization3
4.3.6 Comparison between radical polymerization and ionic polymerization

(2)The Monomer Structure

  • Conjugated alkene monomers can be polymerized by three mechanisms.
  • Annular monomers and carbonyl compounds, for their comparatively high polarity, commonly are not able follow the radical polymerization, but apt to polymerize in ionic or stepwise ways.
4 3 6 comparison between radical polymerization and ionic polymerization4
4.3.6 Comparison between radical polymerization and ionic polymerization

(3)the Effect of the Solvent

In the radical polymerization a solvent only takes part in the chain transfer and can affect the initiator decomposition rate.

  • In the ionic polymerization the polarity and solvating power of the solvent greatly affect the state of active centers of the initiation and propagation. The state can be from covalent association, compact ion pairs, incompact ion pairs to ion free.
4 3 6 comparison between radical polymerization and ionic polymerization5
4.3.6 Comparison between radical polymerization and ionic polymerization

(3)The Effect of the Solvent

TheIonic polymerization can use a nonpolar hydrocarbon solvent , and other solvents can only be used selectively.

  • The Cationic polymerization can use alkyl halide , CS2, liquid SO2 and CO2 as the solvent.
  • The anionic polymerization can use liquid ammonia , liquid chlorine and ether as the solvent.

The rules cannot be used inversely, otherwise the chain transfer or termination will occur.

4 3 6 comparison between radical polymerization and ionic polymerization6
4.3.6 Comparison between radical polymerization and ionic polymerization

(4)The Polymerization Temperature

  • The radical polymerization temperature , which is around or more than 50~80℃ , depends on the requirement of the initiation.
  • The initiating activation energy of the ionic polymerization is quite low. To prevent side reaction , like chain transfer and rearrangement , the ionic polymerization often occurs under low temperature , where the reaction can also get a rapid enough rate.
4 3 6 comparison between radical polymerization and ionic polymerization7
4.3.6 Comparison between radical polymerization and ionic polymerization

(5)The Polymerization Mechanism

  • The inhibitor of radical polymerization commonly is oxygen , benzopuinone and substances that stabilizes radicals. They usually have no inhibitive effect.
  • Polar substances , like water and alcohol , are all inhibitors of the ionic polymerization.
  • Acids are inhibitors of the anionic polymerization.
  • Alkali are inhibitors of the cationic polymerization.
4 4 coordination complex polymerization1
4.4 Coordination Complex Polymerization
  • 4.4.1 Steric regularity of polymerization
  • 4.4.2 Ziegler-Natta polymerization of

nonpolar alkene monomer

  • 4.4.3 Coordination polymerization of

dialkene monomer

  • 4.4.4 Polymerization of π-allyl complex

compound and chromic oxide catalyst

slide85

4.4 Coordination Polymerization

Development History:

  • 1953,German chemist Karl Ziegler
  • 1954,Italy chemist Natta
  • 1955,realizing the industrialisation of low

pressure polyethylene

  • 1957,realizing the industrialisation of

stereoregular polypropylene

  • 1963,Ziegler and Natta accepted the Nobel

chemistry prize

4 4 1 stereoregularity of polymer
4.4.1 Stereoregularity of Polymer

(1) Isomers of Polymer

What is isomerism?

The atoms or atomic groups in a polymer molecule have different interconnection orders, which bring out isomerism or structural isomerism.

Fox example:Polymerizing same or different monomers can produce polymers of same chemistry constitute and different structures.

1 isomers of polymer
(1) Isomers of Polymer
  • For example , polymer with structure unit -[ C2H4O-] n can be polyvinyl alcohol or polyethylene oxide

polyvinyl alcohol

polyethylene oxide

slide88

(1) Isomers of Polymer

  • Fox example , PMMA and polyethyl acrylate , and polyamide , like nylon-6 and nylon一66 ,are all isomers with different properties.

PMMA

polyethyl acrylate

Nylon-6

Nylon-66

1 isomers of polymer1
(1) Isomers of Polymer
  • With different interconnection forms among structure units , sequence isomerism occurs.
  • For example , isomerism phenomenon of head-end connection and head-head connection . Polymers of head-end , head-head and random interconnection have the same chemistry composition , while their properties differ.
2 solid isomers of polymer
(2)Solid Isomers of Polymer

Solid Isomerism:

Solid isomers of polymer indicate the kind of polymers , which have the same chemistry constitute and connection structure , and differs just in conformation , that is to say , the steric arrangements of them are different.

Solid isomerism can be classified into two categories:

slide92
One is caused by the chiral center, calls optical isomer.

R (Right) form & S (Left) form

  • The other kind is caused by the double bond, called geometry isomer.

Z(cis conformation)& E(trans conformation)

2 solid isomers of polymer1
(2)Solid Isomers of Polymer

How to distinguishconfigurationandconformation

  • Conformation-----indicates the steric isomerism caused by the difference in steric arrangement of atoms.
  • Unless chemistry ruptures , the two confor-mations can never transform.
slide94
Configuration-----describes the difference in the molecular state , which caused by the C—C single bond internal rotation . For example , forms of zigzag molecule , random coil , helix chain , folded chain .
  • Configurations can intertransform by a sequence of internal rotation of the single bond.
2 solid isomers of polymer2
(2)Solid Isomers of Polymer

① Optical Isomers

All monomers with the chiral center in the framework atoms can form polymers of different steric structures.There are chiefly three possibilities when monomer inserts polymer chain.They are:

  • Isotactic polymer
  • Syndiotactic polymer
  • Random polymer
chart 4 4 steric chemistry structure of macromolecular a isotactic b syndiotactic c random
Chart 4-4 Steric Chemistry Structure of Macromolecular(a)-Isotactic,(b)-Syndiotactic,(c)-Random
2 solid isomers of polymer3
(2)Solid Isomers of Polymer

② Geometry Isomers

When substitute on the double bond or ring have different steric arrangements , several geometry isomers form.

For example:

Polydiolefine in the form of 1,4 addition, have

cis 1,4 addition and trans 1,4 addition,

see Chart 4-5

slide98

Trans form 1,4-polymer

Cis form 1,4-polymer

geometry isomers
② Geometry Isomers
  • So polymer of methyl butane have six kinds of isotactic polymers . They are:
  • All cis-1,4 addition ,all trans-1,4 addtion polyisoprene ;
  • Isotactic-1,2 addtion , syndiotactic-1,2 addition polyisoprene ;
slide100
Isotactic-3,4 addition , syndiotactic-3,4 addition polyisoprene .
  • Random polymers could also forms , like random 1,4-,1,2- and 3,4-addition polymer.
3 properties of isotactic polymer
(3)Properties of Isotactic Polymer
  • The conformation and conformation regula-

rity greatly affects the material property.

  • According to performance requirement ,

regular polymers of different conformations

should be produced.

For example , isotactic and atactic PP greatly differs in properties.

3 properties of the isotactic polymer
(3)Properties of the Isotactic Polymer
  • Random PP is amorphous , soft and sticky , which have no physical intensity and little usage.
  • Isotactic PP have high crystallinity and a melt point of higher than 175℃;
  • Having high intensity and light gravity;
slide103
With solvent resistance and good chemistry corrosion resistance;
  • Widely used in plasticity and fiber material , being big polymer material with cheap price and high performance .
3 properties of isotactic polymer1
(3)Properties of Isotactic Polymer
  • High cis-1,4-polybutadiene or polyisoprene is a important commercial systhesis rubber material , with good chain flexibility and very low Tg and Tm.
  • High trans 1,4-polydialkene ,used as a plasticity and hard rubber material , have low chain flexibility , less configuration and high Tg and Tm, and is apt to crystallize .
slide105
Random polymer have bad performance in physical mechanical property.
  • Products of isotactic polymers of different conformations will meet diverse requirement and have different commercial value.
3 properties of the isotactic polymer1
(3)Properties of the Isotactic Polymer

The structure units of natural polymers , cellulose and starch , are both glucose unit , of which the steric conformation differs , so properties are greatly divergent.

β-D-(+)-glucose

α-D-(+)-glucose

3 properties of the isotactic polymer2
(3)Properties of the Isotactic Polymer

The differences in the structure cause that:

  • Cellulose has high crystallinity degree , intensity and mechanical performance , low solubility , and hardness in hydrolysis . It is used as structural material in both plant and material .
slide109
Starchis apt to hydrolyze , and has a so bad crystallinity that it cannot be used as structural material , and just take a part as energy depositing material in food and propagations .
4 4 2 ziegler natta polymerization of nonpolar alkene monomer
4.4.2 Ziegler一Natta polymerization of nonpolar alkene monomer

Polymerization of the alkene monomer initiated by a Ziegler一Natta catalyst can produce an unbranched , stereoregulated polymer . PP gained in this way is linear and has a higher density than that produced in the radical polymerization .

PP synthesized by Ziegler-Natta polymerization is isotactic and of excellent material property . Many nonploar alkene monomers are able to process the coordination complex polymerization .

1 constitute of ziegler natta catalyst
(1) Constitute of Ziegler一Natta catalyst
  • The Ziegler-Natta catalyst is a general designation of a category of catalyst system .
  • It commonly consists of two compositions
  • Sometimes the third compositionis added to reduce the quantity of cocatalyst.
  • Superfine carrier powder is also introduced to make the active coordination catalyst adhere to the carrier surface to reduce the quantity of the catalyst , enhance catalyst effectiveness , and get highly effective catalysis system .
main catalyst
① Main Catalyst
  • The Main catalyst is the compound consisting of transitional metal elements of subgroups, from IV to VIII , in the periodic table.
  • There are d electron orbit , which can accept coordination from the election donator , in the electron structure of this kind of metal atoms.
  • These transitional metal compounds are chiefly the halides or halide oxides of titanium , vanadium , chromium , molybdenum , and zirconium .
cocayalyst
② Cocayalyst
  • The Cocatalyst is the organic compounds of metals of main groups, from I to II . The commonly used ones are the alkyl , aryl or hydride compounds of Al , Li , Mg and Zn .
  • The most commonly used system consists of TiC14 or TiC13 and alkyl aluminium . The catalysis system can be of heterophase or homophase , which separately mostly consist of titanium or vanadium catalyst system .
  • The constitute of the catalyst system affects the yield ratio , chain length and degree of isotacticity .
slide114

A Real catalystis not a simple coordination of two compositions. It gets high catalysisactivity through an aging progress , in which there is complicated alkylating reduction reaction .

The most important feature is that the transitional metal is reduced from the high oxidation state to the low oxidation state and gets unfilled coordination value state . It`s the real activation center .

effect of catalyst
Effect of Catalyst:
  • a. initiating or supplying initiating spike;

Initiating ability is expressed by catalyz-

ing activity index:

g(PP)/g(Ti)

  • b. orientating : expressed by IIP of product.
the third constitute
③ The Third Constitute
  • Lewis alkali with electron donating ability , like compounds with N , O or P;
  • Often can enhance the activity of the double composition catalyst;
slide117
Elevate stereotacticity and MW of the product;
  • The function of the third composition , which is electron donating , is to take advantage of the difference in coordination ability to reproduce the cocatalyst .
the third constitute1
③ The Third Constitute

For example , amine , ether and some compounds with phosphor , expressed by B: , have the ability to coordinate kinds of aluminous compounds, though the degrees of the coordination ability are different and the stability follows the subjacent order :

B:→AlCl3 > B:→AlRCl2 > B:→AlR2Cl >B:→AlR3

the third constitute2
③ The Third Constitute

Alkyl aluminium compound processes alkylating reduction reaction during the forming of the catalyst :

Complex Competition Reaction

With low quantity of the third composition , enough cocatalyst can be reproduced . Usually Al:Ti:B approximately equals 2:1:0.5 in industry .

high performance catalyst carrier
④ High Performance Catalyst Carrier

Duing the producing of Ziegler-Natta heterophase catalyst , only catalyst on the surface can form polymerization catalysis active centers , and the interior of granule doesn`t effect and waste the catalyst .

Highly Dispersion of Catalyst On Carrier Surface

Using Superfine Granule Carrier

High-Performance Catalyst

high performance catalyst carrier1
④ High Performance Catalyst Carrier

Superfine Granule Carrier ----For example , granules of Mg(OH)Cl , MgC12 and Mg(OH)2 make the newly produced catalyst highly disperse on the surface of the carrier .

The active surface increases from 1~5 m2/g to 75~200 m2/g , producing so-called High-Performance Catalyst.

slide122
With this kind of the catalyst no less than 3×l05 g/g Ti PP gains , while without the carrier 3×l03 g/g Ti produces . The quantity of the catalyst in product is low , and there`s no need to remove catalyst remainder .

With as high stereo tacticity as more than 95% , the stability and life will increase .

table 4 8 the effect of initiator constitute to isotacticity degree of pp
Table 4-8 The Effect of Initiator Constitute to Isotacticity Degree of PP

Alkyl metal compound Transitional metal compound Quantity of isotactic structure

AlEt3 TiCl4 30~60

AlEt3 TiBr4 42

AlEt3 TiI4 46

AlEt3 VCl4 48

AlEt3 ZrCl4 52

AlEt3 MoCl4 50

AlEt3 TiCl3 (α,γ,δ) 80~92

BeEt2 TiCl3 (α,γ,δ) 94

AlEt2I TiCl3 (α) 98

the spike is a complex consisting of two kinds of metals
The Spike is a complex consisting of two kinds of metals

1. Single TiCl3 have no initiating activity;

2. The more the aluminium alkyl associating with Ti in the system is , the high the initiating activity is.

2 orientation mechanism of alkene coordination polymerization
(2)Orientation Mechanism of α-alkene Coordination Polymerization

There are two typical coordination polymerization mechanisms , which are accepted commonly.

  • Single metal mechanism-----Alkene monomer coordinates at the voidance of transitional metal;
  • Double metal mechanism----- Transitional metal and aluminium atom form an electron deficlent bridge bond , on which they accept the coordination from the alkene monomer.
single metal catalysis mechanism
① Single Metal Catalysis Mechanism

Alkene monomer coordinates at a voidance of single metal.

Transitional metal coordination octahedron

Forming four membered ring transition state with the

organic group on the ortho position

(a)

Chart 4-7 Conventional Diagram of Single Metal Coordination Complex Polymerization Mechanism of Alkene

(b)

slide127

Case I:

(c)

slide128

Case II:

(d)

So if the voidance jump finishes before the new monomer coordinatingly takes the available space , all of the insertingly propagating monomers will coordinate at the same position , and the propagating chain structure unit will have the same geometry conformation.

the single metal catalyst mechanism
① The Single Metal Catalyst Mechanism
  • If vacancy fly occurs and the procession is in α-substituted alkene polymerization, the isotactic polymer gains.
  • If vacancy fly can`t process , the alkene monomer alternately insertingly propagates in two vacancies and gains the syndiotactic polymer .
slide130
If coordination competes with fly , their stereo tacticity will change . Obviously the structure and reaction condition of the active center , and the steric hindrance of the alkene monomer substitute both determine the geometry conformation of coordination and inserting propagation .
the double metal catalyst mechanism
② The Double Metal Catalyst Mechanism

The Alkyl group locates on the bridge bond between the two metals.

(b)

(a)

Electron deficient four membered ring

Coordination transition state

continuing

The monomer insert titanium-carbon weak bond and alkyl R transposes from Ti metal to the other carbon atoms of alkene.

Continuing:

(d)

(c)

Carbon atom of alkene and double metal then forms new bridge bond.

Six membered ring

slide133
In the same mode , the alkene monomer can continuously coordinate and insertingly propagate to form the polymer chain.
the double metal catalyst mechanism1
② The Double Metal Catalyst Mechanism

The above two mechanisms only explain the basic feature of the coordination polymerization and are commonly accepted , but both have bugs.

slide135
Because the coordination complex catalysis system is complicated , which is affected by factors of homophase , heterophase and the third composition, and with different compound components, the activity and orientation degree varys, as shown in table 4-8 . Simple theory model cannot explain these complicated phenomena.
3 mechanism of alkene coordination polymerization
(3)Mechanism of α-alkene Coordination Polymerization

Ziegler-Natta coordination polymerization still belongs to chain the polymerization , consisting of every elementary reaction of the chain polymerization.

Chain Initiation:

Chain Propagation:

3 mechanism of alkene coordination polymerization1
(3)Mechanism of α-alkene Coordination Polymerization

Chain Transfer:

① Transfer to alkyl metals of family Ⅰ~Ⅲ

slide139

Chain Transfer:

③ Transfer to H2 , the MW regulator

3 mechanism of alkene coordination polymerization2
(3)Mechanism of α-alkene Coordination Polymerization
  • All of chain transfer can terminate the macromolecular chain and apt to lower MW . But it still have activity to catalyze polymerization , and the kinetic chains are not terminated , which have a feature like living polymerization , while the MWD is quite wide .
slide141

Because the metal atom is apt to form a metal hydrogen bond , all the chain transfer, except hydrogen is addition reaction, summed up to be caused by the transfer of unstable β hydrogen . A Metal ion is apt to produce a metal hydrogen bond . All chain transfer except hydrogen addition reaction could be summed up to be composed of the transfer of unstable β hydrogen anion .

slide142

Chain Termination:

Spontaneous chain transfer to β-hydrogen anion

3 mechanism of alkene coordination polymerization3
(3)Mechanism of α-alkene Coordination Polymerization
  • The higher the concentration of transition metal compound and the tinier the produced granule is , the higher the polymerization rate is .
  • Elevating the concentration of alkylating reagent has various influences:
if the concentration of aluminium alkyl is too high the mw of polymer will reduce
If the concentration of aluminium alkyl is too high , the MW of polymer will reduce .
  • Elevating the quantity of the alkylating rea-

gent will increase activation centers and the

polymerization rate . There is a optimum ratio

between the chief catalyst and the cocatalyst ,

which usually is about 1:2 (Ti:Al) .

  • The quantity of MW regulator H2 lowers not only DP but also the polymerization rate .
4 4 3 coordination of diene monomers
4.4.3 Coordination of diene monomers
  • The Diene monomer can produce stereoregular polymer in the Ziegler-Natta catalysis polymerization .
  • The Ziegler-Natta catalysis polymer-ization progress of diene have a little differences from that of single alkene .
slide146
At the beginning of the polymerization the diene monomer and transitional metal atom form a π-allyl complex compound , and the propagating progress is still the insertion between metal and carbon bond and the continuous one-after-one addition of the monomer .
4 4 3 coordination of diene monomers1
4.4.3 Coordination of diene monomers
  • Ziegler-Natta catalysts with different consti-tutes and compositions greatly differ in micro-structure of the diene coordination polymer-ization .
  • In this way many kinds of products of polybutadiene and polyisoprene with different structures .

For example: High cis-1,4 addition polymer or high trans-1,4 addition polymer , and 1,2 or 3,4 addtion polymers ,.etc.

4 4 4 polymerization of allyl complex compounds and chromic oxide catalyst
4.4.4 Polymerization of π-allyl Complex Compounds and Chromic Oxide Catalyst

(1) The Mechanism of the Coordination Polymer-

ization of the π -allyl Complex Compouund

On Ziegler-Natta catalyst , the diene monomer can coordinate to form π——allyl complex compound and bring out the polymerization .

This kind of the activation center of cataly-sis polymerization can be produced by the direct reaction of the allyl compound and the transi-tional metal compound .

slide150
Fox example:

transitional metal halide ,like nickel , chro-mium, cobalt, iron, titanium, vanadium, moly-bdenum, tungsten and niobium, can form poly-merization catalysts of high activity.

(π-C4H7)2Ni,(π-C4H7)2Cr,(π-C4H7)3Nb,

(π-C4H7)4Ti 或 (π-C4H7)4Zr

1 coordination mechanism of allyl complex compounds
(1) Coordination Mechanism of π-allyl Complex Compounds

Л-allyl catalyst complex compound have its own coordination structure . When the monomer inserts among the metal carbon bonds and take 1,4 addition , as the following reaction equation shows, cis-1,4-polybutadiene is produced .

1 coordination mechanism of allyl complex compounds1
(1) Coordination Mechanism of π-allyl Complex Compounds

If the position that the monomer inserts is not on the M-C (1) bond but on the M-C (3) bond , 1,2 or 3,4 addition occurs shown by the following reaction equation.

2 polymerization catalyzed by chromic oxide
(2)Polymerization Catalyzed by Chromic Oxide

A Catalyst of orientation, in which chromic oxideis most commonly used, is the metal oxide formed on the surface of inert granula of silica gel or aluminum oxide.

The catalysis function of this kind of catalysts is caused by the ability of the chromium ion to change its oxidation state.

chapter 4 ionic ring opening controlled polymerization
Chapter 4 Ionic, Ring-Opening & Controlled Polymerization
  • 4.1 Overview
  • 4.2 Cationic Polymerization
  • 4.3 Anionic Polymerization
  • 4.4 Coordination Complex Polymer-

ization

slide155
4.5 Ring-Opening Polymerization
  • 4.6 Group Transition Polymerization
  • 4.7 Atom Transition Radical Polymerization
4 1 overview
4.1 Overview

Some monomers, like alkenes and substances with rings, can undertake ionic chain polymerization with a ionic initiator.

slide157

4.1 Overview

  • 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
4 1 overview1
4.1 Overview

(1)The active center of cationic polymerization is a

carbocation:

(2)The active center of anionic polymerization is a

carboanion

4 1 overview2
4.1 Overview

(3)The active center of coordination poly-

merization is coordinated ion with a

metallic carbon bond.

feature and industrial value of ionic polymerization
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.
slide161
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.
ring opening polymerization
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

Like O,N,S, -CH=CH- , -CONH-, -COO-,.etc.

With groups like ether,ester, amide, imine and double bond etc.

ring opening polymerization could also be used to synthesize polymer from monomer
Ring-Opening polymerization could also be used to synthesize polymer from monomer.
  • For example, polyamine can be prepared from caprolactam, and polyformaldehyde,which is used as a engineering plastics, can be produced from trioxymethylene.
slide164

Development of Ring-Opening Polymerization

  • Ring-Opening polymerization has been developed and studied since 1950s. A lot of products which have been indus-trialized, such as, polycaproamide, polyformaldehyde, polytetrahydrofuran, polyethylene oxide, polypropylene oxide etc. As the late direction, isomerized ring-opening polymerization of cycloolefin and spirocyclic monomer have been studied.
controlled polymerization
Controlled Polymerization

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

controlled polymerization1
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.
slide167
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.
4 1 cationic polymerization
4.1 Cationic Polymerization
  • 1839 ---- The First cationic polymerization,in which styrene is polymerized with tin tetrachloride, was not realized as it, for there was no polymer concept then.
  • 1873-----Vinyl ether is polymerized by acid or metal halide.
  • 1884----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.
slide169
The cationic polymerization of isobutylene 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.
4 1 1 initiator and monomer
4.1.1 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)

4 1 1 monomer and initiator
4.1.1 Monomer and Initiator
  • 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 4-1

table 4 1 cationic initiator
Table 4-1 Cationic Initiator

InitiatorTypical Substances

1.Strong proton acid H2SO4,HClO4,H3PO4,

Cl3COOH…

2.Lewis Acid BF3 , BF3O(C2H5)2,

BCl3,TiCl4,TiBr4 ,

AlCl3 , SnCl4

the initiator and coinitiator of a lewis acid
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.
  • To cut the side reaction,cationic polymerization

almost take place under low temperature,and the

solvent must be inert and very dry.

4 1 2 cationic polymerization mechanism
4.1.2 Cationic Polymerization Mechanism

Cationic polymerization belonging in chain polymerization,contains:

  • Initiation,
  • Propagation,
  • Transfer,
  • Termination.
1 initiation2
(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.
1 initiation3
(1) Initiation
  • A Lewis acid initiator firstly react with a cocatalyst, and then dissociate into a proton. The process is shown as the following reaction equation.
the proton adds onto a monomer to produce a monomer carbocation
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.
2 propagation3
(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.
slide180

(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:
2 propagation4
(2) Propagation

Free ion

Loose ion pair

Covalent bond

Intimate ion pair

isomerization polymerization
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.
slide183

CH3

-[-CH2—C6H5—C--]n—

CH3

isomerization polymerization1
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.
3 transfer1
(3)Transfer
  • Under high temperature,the chain transfer can be found evidently.
  • The chain transfers to a monomer:
3 transfer2
(3)Transfer
  • The chain transfers to a gegenion:
4 termination3
(4)Termination

1. Combination with gegenion,for example:

4 termination4
(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 is stabilized by solvating around the proton so that can`t initiate the polymerization to terminate the reaction any more.

slide190

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.

4 1 3 kinetic
4.1.3 Kinetic

(1) The rate equation

Conveniently,the following general equations can be used to show elementary reactions of the cationic polymerization,where:

  • C-initiator
  • RX-coinitiator
  • M-monomer

(2) The degree of polymerization

1 the rate equation1
(1) The rate equation

Chain Transfer

Termination

1 the rate equation2
(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.
the rate equation of the polymerization with an ion pair active center
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]

(4-1)

(4-2)

slide197
Treated with stable-state s, Ri = Rt, so
  • The rate equation of the polymerization with an ion pair as a spike is:

(4-3)

(4-4)

1 the rate equation3
(1)The rate equation
  • The polymerization with a free ion as a spike has a similar expression.
  • The values of kinetic rate constant kp and kt prominently differ with different spikes.
1 the rate equation4
(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 spike, 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:

(4-5)

1 the rate equation5
(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:

(4-6)

According to the following equation:

1 the rate equation6
(1) The rate Equation

(4-7)

(4-8)

(4-9)

2 the degree of the polymerization dp
(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:

(4-10)

slide203
(2) DP
  • The rate equation of the chain transfer (4-11)

Substituting it into (4-10), the expression of DP

is(4—12)

slide204
(2) DP

(4-12)

Its reciprocal form is more commonly applied,

and ktrM / kp is substituted by the chain transfer

constant:

(4-13)

slide205
(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:

(4-14)

+

slide206
(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(4-13).
  • The monomerward chain transfer constant CM , which is the second term in the right of the equation, is independent of the concentration of monomer.
slide207
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.
3 influence of temperature
(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.
slide209

The effect of the temperature on the polymerizing rate depends on the relation between kp/kt or kp‘/kt’ and the temperature. The symbols without primes represents ion pairs, and the other represents free ion. So the arrhenius form of the rate constant ratio of one kind of those two symbols is:

the effect of the temperature on the polymerization rate
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 , andis negative.
slide211
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.
the effect of the temperature on dp
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.
4 influence of solvent and gegenion
(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 spike of the ion polymerization is mostly ion pairs or free ions in the equilibrium state。
4 influence of solvent and gegenion1
(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(+) (4-17)

α is the degree of dissociation from ion pairs to free ions

slide215

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

4 influence of solvent and gegenion2
(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.
slide217

Table 4-2 The Effect of Solvent on the Cationic Polymerization of Styrene(HClO4 as a initiator)

Solvent Dielectric ConstantKp/25℃,l/mol.s

CCl42.30.0012

CCl4/(CH2Cl)2,40/605.160.40

CCl4/(CH2Cl)2,20/807.03.2

(CH2Cl)29.7217.0

4 influence of the solvent and gegenion
(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.
4 influence of solvent and gegenion3
(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。
4 influence of the solvent and gegenion1
(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.
slide221

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 spike is high, the rate of the cationic polymerization is much higher than that of the radical polymerization.