1. Chapter 5 Ionic Chain Polymerization

2. Chain Polymerization
Initiation : Initiated by a reactive species R* produced from some compound I termed an initiator:
Propagation: The reactive species (free radical, cation, or anion) adds to a monomer molecule by opening the -bond to form a new active species. The process is repeated as many more monomer molecules are successively added to continuously propagate the reactive center.
Termination : Polymer growth is terminated at some point by destruction of the reactive center by an appropriate reaction depending on the type of reactive center and the particular reaction conditions.

3. 3-1 NATURE OF RADICAL CHAIN POLYMERIZATION
3-1a Comparison of Chain and Step Polymerizations
Chain Polymerizations
Step Polymerizations
only monomer and the propagating species can react with each other
two molecular species present can react each other
The monomer concentration decreases throughout the course of the reaction
Monomer disappears much faster
The MW of the polymer is relatively unchanged during the polymerization
(Radical)
The MW increases throughout the course of the reaction

4. - C=C (Vinyl monomers ) and C=O (aldehydes and ketones) bonds are the two main types of linkages that undergo chain polymerization.
- Aldehydes and ketones are polymerized by both anionic and cationic initiators
- Vinyl monomers can undergoes polymerization by both radical and ionic initiators.

6. 5-1 Comparison of Radical and Ionic Polymerizations
Monomer
Radical polymerization : almost all vinyl compound
Ionic polymerization : very selective
ex)Anionic : vinyl compound w/ e.w.g.
Cationic : vinyl compound w/ e.d.g.
Electron donating substituents (alkoxy, alkyl, alkenyl, and phenyl)
isobutylene, styrene, methyl vinyl ether, and isoprene :
- cationic polymerization by cationic initiators.

7. Electron-withdrawing substituents (such as cyano, aldehyde, ketone, acid, or
ester) → anionic polymerization
Alkenyl and phenyl substituents can resonance stabilize the anionic propagating
species → anionic polymerization
Halogens : withdraw electrons inductively and push electrons by resonance, but both effects are relatively weak: neither anionic nor cationic polymerization vinyl chloride → radical polymerization

8. Radical & condensation polymerizations are well defined,
while ionic polymerizations are not. Why?
Experimental difficulty
: difficult to get reproducible data
∵propagating sites are carbocations or carbanions, then very rapid rates
⇒ very reactive extremely sensitive to impurity
such as moisture, oxygen,……
2) Reaction media is not clear
: initiator, propagating molecule can be heterogeneous

9. Similar characteristics of cationic and anionic polymerizations
Polymerizations depend on the formation and propagation of ionic
species, a positive and negative ones.
2) high-molecular-weight products can be obtained when the propagating
centers are stabilized by solvation (long life time)
3) Relatively low or moderate temperatures are required to suppress
termination, transfer, and other chain-breaking reactions
Solvents for ionic polymerizations
Highly polar solvents are desirable, while they cannot be used.
- polar hydroxylic solvents (water, alcohol) react with ions
- ketones can form highly stable complexes with initiators
2) Therefore moderately polar solvents are used
- tetrahydrofuran, ethylene dichloride, and pentane

10. Characters of propagating chain end in cationic polymerization
⇒ polar covalent bond(Ⅰ)
contact (tight) ion pair(Ⅱ)
solvent-separated(or loose) ion pair(Ⅲ)
free ion(Ⅳ)
Ⅰ and Ⅱ → living carbocationic polymerization
Ⅲ and Ⅳ → conventional uncontrolled carbocationic polymerization
Other classification
Free ion : Ⅳ
Ion pair : Ⅱ, Ⅲ
Covalent species : Ⅰ ⇒ very slow or no reaction ⇒
Major propagating species : II, III, IV in most ionic polymerization
Coexisting in equilibrium with each other

11. Effect of solvent on the ion pair
In general free ion concentration are much smaller than ion pair concentration,
- In anionic polymerization, free ions are orders of magnitude higher in reactivity
than ion pairs.
 Free ions are reactive than ion pair more than 10 times !
In cationic polymerization, free ions are less than an order of magnitude higher in reactivity than ion pairs.
 Free ions are reactive than ion pair less than 10 times !
Effect of solvent on the ion pair
High polarity solvent → loose ion pair (Ⅲ)
Low polarity solvent → tight ion pair (Ⅳ)
⇒ (+) & (-) charge separation is easier for high polarity solvent`
⇒ III and IV also have different reactivity

12. Solvent effect on anionic & cationic polymerization
Cationic : ⇒ [(BF3)OH]-, (AlCl4)-
Larger counter ion : non reactive
∴ less affected by solvent polarity
therefore even less polar solvent can make ion pair
Anionic : ⇒ Li+, Na+
Small counter ion
∴ much more solvent-dependent
Termination in ionic polymerization
By the rxn of propagating chain with counter ion, solvent, or other species
Not by the bimolecular reaction between two propagating polymer chains
Comparing cationic and anionic polymerizations, anionic systems are more reproducible because the reaction components are better defined and more easily purified

13. 5-2 CATIONIC POLYMERIZATION OF THE CARBON–CARBON DOUBLE BOND
5-2a Initiation
5-2a-1 Protonic acid (Brønsted acid)
A- should not be nucleophilic
∴ HCl cannot be used as an initiator.
Possible initiators
Perchloric, sulfuric, phosphoric, fluoro, chlorosulfonic, methanesulfonic, trifluoromethanesulfonic acids
⇒ Large counter ion, A- , just stabilize carbocation by solvation or complexation
Still max. M.W. obtained is a few thousand
∵ A- is still reactive

14. 5-2a-2 Lewis acid (+generally coinitiator) ⅰ) Lewis acid
Metal halide : AlCl3, BF3, SbCl5, ZnCl2, TiCl4
Organometallic derivatives : RAlCl2, R2AlCl, AlR3
Oxy halide : POCl3, Cr2OCl
ⅱ) Coinitiator
Proton donor (protogen)
→ H2O, HX, alcohol, carboxylic acid
Carbocation donor (cationogen)
→ t-butyl chloride, triphenylmethyl chloride
Ex)
⇒ BF3OH- & AlCl4- : large & much less nucleophilic
∴ high M.W. can be obtained
ⅲ) General initiation process by Lewis acid
I : coinitiator
ZY : initiator
M : monomer

15. ※ Self-ionization
Without coinitiator, higher strength Lewis acid (AlCl3, TiCl4, etc.)
∴initiation is possible
Ex)
Increased initiation of Lewis acid mixture

16. Evidence of self-ionization
→ H2O conc. in the commenc glove box : 10-3M
∴ H2O can act as coinitiator at any time
Using sterically hindered pyridine (SHP)
→ Proton scavenger : react w/ H+, but not with Lewis acid or carbocation scavenger ∵ steric hindrance
- SHP + monomer + only Lewis acid
1) If inhibition occurs, then SHP is reacted w/ H+
⇒ initiation w/ H2O (coinitiator) in the glove box
2) If there is no inhibition, SHP is reacted w/ H+, while it does not affect
the polymerization
⇒ initiation by self-ionization
initiation w/o H2O

17. Activity of an initiator/coinitiator complex
⇒ depend on the ability to donate a proton or carbocation to monomer
General rule
K & ki : both increase w/ increasing acidity of Lewis acid and coinitiator
Ex) Lewis acid
AlCl3 > AlRCl2 > AlR2Cl > AlR3 : the more Cl, the higher acidity
AlR2I > AlR2Br > AlR2Cl : I > Br > Cl
HCl > CH3COOH > PhOH > H2O > alcohol
→ protonic acid : coinitiator
Exceptions
Boron halide + H2O
acidity: BBr3 > BCl3 > BF3
activity (K & ki) : BF3 > BCl3 > BBr3
⇒ due to hydrolysis of BX3
Hydrolysis reactivity
BBr3 > BCl3 > BF3

18. Cationogens for initiator
Primary & secondary halide are ineffective for initiation
∵ Carbocation is not easily formed
∴ Tertiary halide is used Ex) t-butyl and 2-phenyl-isopropyl(cumyl halide
⇒ is formed : having similar stability compared to or
less stable than
Ex)
trityl halide cycloheptatrienyl halide
⇒ more stable than the propagating chain end of styrene & isobutylene
∴ Cannot be used as coinitiator ⇒
Propagating radical

19. However they can be used for vinyl carbazole, p-methoxystyrene, vinyl ethers, indene.
Acylium ions (oxacarbocations) have also been used to initiate cationic polymerization

20. ratio of initiator to coinitiator
→The polymerization rate increases with increasing [initiator]/[coinitiator], reaches a maximum, and then either decreases or levels off.
The decrease in rate at higher initiator concentration
1) the inactivation of the coinitiator by initiator
such as SnCl4-H2O may involve
hydrolysis of Sn-Cl bonds to Sn-OH.
2) The formation of oxonium salt (IV), too unreative
SnCl4-initiated polymerization rate of styrene in carbon tetrachloride at 25 oC. Symbols o (0.08 M) and  (0.12 M) initiator concentrations

21. Initiation by some organo transition metal complexes
- complex formed from cyclopentadienyltrimethyltitanium
and triperfluorophenyl boron initiates polymerization

22. 5-2a-3 Halogen
Chlorine, bromine, and iodine act as cationogens in the presence of the
more active Lewis acids such as trialkylaluminum or dialkylaluminum halid.
The unique feature of iodine
It can initiate the more active monomers such as styrene, vinyl ether,
acenaphthylene. N-vinylcarbazole
Iodine adds to the double bond to form a diiodide that eliminates
hydrogen iodide. The hydrogen iodide generated by this process acts as the
cationogen with iodine acting as a Lewis acid to form the initiating system.

23. 5-2a-4 Photoinitiation by Onium Salts
Aryldiazonium (ArN2+Z-), diaryliodonium (Ar2I+Z-), and triarylsulfonium (Ar3S+Z-)
salts, where Z- is a nonnucleophilic and photostable anion such as tetrafluoroborate (BF4), hexafluoroantimonate (SbF6), and tetraperfluorophenylborate [(C6F5)4B-],
and hexafluorophosphate (PF6), are effective photoinitiators of cationic
polymerization
Cationic photoinitiators are used in coatings, printing inks, adhesives, sealants, and photoresist applications. Most of the applications involve vinyl ether polymerizations or ring opening polymerizations of epoxy monomers.

24. 5-2a-5 Electroinitiation
initiatied by cations formed via electrolysis of some component of the
reaction system (monomer, solvent, electrolyte, or other deliberately added
substance)

25. 5-2a-6 Ionizing Radiation
Cationic polymerization initiated by ionizing radiation is markedly different
from other cationic polymerizations in that the propagating species is a free ion remote from a counterion. Overall electrical neutrality is maintained by
electrons trapped by the monomer.

26. 5-2b Propagation
⇒ Rearrangement in propagation (or isomerization) is possible due to 1,2-hydride & 1,2-methide shift
polymerization of 3-methyl-1-butene
Because other carbocations are of comparable stability

27. Cationic polymerization of 4-methyl-1-pentene
Monomers w/o rearrangement,

28. Other isomerization polymerization
1. Intra-inter molecular polymerization
→ conjugated dienes
Ex)
2. Transannular polymerization
Ex1)

29. Polymerization by strain relief
Ex2) 5-methylene-2-norbornene
Polymerization by strain relief
Other polymers
Less sterically hindered
Carbocation stability

30. 5-2c Chain Transfer and Termination
5-2c-1 β-Proton Transfer
1. Chain transfer to monomer ; + charge is transferred to monomer
ⅰ) Transfer of a β-proton (proton transfer)
ⅱ) Hydride ion transfer from monomer (hydride transfer form the H in sp3 C)
∴ For isobutylene ⅰ) is major C.T. to monomer rxn β

31. 2. Chain transfer to counter ion※
⇒ Only proton transfer is possible, while
hydride transfer is not possible for these monomers
※ If the rxn temp. is higher than 20℃,
the C.T. to monomer can be principle rxn that limits M.W.
Below 20℃, C.T. to monomer is not significant.
∵ C.T. involves bond cleavage – need high activation E
2. Chain transfer to counter ion
: spontaneous termination
⇒ This termination should not be a dominant compared to C.T. to monomer
※ Polymer chemists are smart enough not to use such initiators

32. 5-2c-2 Combination with Counterion
→ when counter ion is nucleophilic : when protonic acid is used as an initiator
※ When Lewis acid was used
Why?
bond strength
: B-F > B-O > B-Cl
kcal/mol or
B-O bond cleavage
B-Cl bond cleavage

33. ※ aluminum alkyl–alkyl halide initiating systems
- Termination by alkylation
- Termination by hydridation:

34. 5-2c-3 Chain Transfer to Polymer
ⅰ) Intra molecular electrophilic aromatic substitution
⇒ Back-biting
ⅱ) Intermolecular hydride transfer to polymer
→ 1-alkene polymerization
: 3o carbocation → branch generated!

35. 5-2c-4 Other Transfer and Termination Reactions
Chain transfer agents XA : present as solvent, impurity, or deliberately added to the reaction system
Reinitiation is possible from
∴ Small amount of H2O : may not affect the polymerization rate
Excess amount of H2O : inhibitor or retarder
∵ hydrolysis of initiators such as MX3
To stop the cationic polymerization
→ Add excess amount of H2O, alcohol, etc.
- amines, triaryl or trialkylphosphines, and thiophene act as inhibitors or retarders by converting propagating chains to stable cations

36. 5-2d Kinetics 5-2d-1 Different Kinetic Situations ⅰ) initiation ex)
ii) propagation

37. ⅲ) Termination → if by combination w/ counter ionEx
Using steady state assumption ∴
※ Radical polymerization

38. 3-3b Rate Expression
Assumption: kp and kt are independent of the size of the radical.
Although Very small radicals are more reactive than propagating radicals, but this effect is not important because the effect of size vanishes at the dimer or trimer size.
The rate of monomer disappearance = the rate of polymerization
Ri and Rp are the rates of initiation and propagation, respectively.
the number of monomer molecules reacting in the initiation step is very very small
Then the polymerization rate is given simply by the rate of propagation

39. [M] : monomer concentration
[M∙] : total concentration of all chain radicals
[M∙] = [M1∙] + [M2 ∙] + [M3∙] + ………..+ [Mn∙] +……
The radical concentration ([M∙]) is very difficult to measure quantitatively,
since they are very low (10-8 M) and is very reactive.
Therefore it is desirable to eliminate [M∙]
How?
“steady-state assumption” : The rate of change of the concentration of radicals quickly becomes and remains zero during the course of the polymerization.
The use of the factor of 2 (conventional number) in the termination rate equation follows the generally accepted convention for reactions destroying radicals in pairs.
Rp ∝ kp , [M], (Ri)1/2, (kt) -1/2

40. If there are chain transfer rxns,
⇒ Chain transfer decrease the while Rp is not affected (in general)
since reinitiation w/ the proton derived from C.T. is fast
; the carbocation generated from C.T. is as reactive as M+ (propagating site)
Exception
: another termination
Using steady state assumption (# of total active site is constant!)
: C.T. to solvent
: C.T. to monomer
: spontaneous termination or C.T. to counter ion
Stable, No reinitiation
∴ dead polymer
Decrease Rp

41. 3-6 CHAIN TRANSFER 3-6a Effect of Chain Transfer
chain-transfer reactions
XA : monomer, initiator, solvent, or other substance
the rate of a chain-transfer reaction
reinitiation
a very small-sized polymer ( 𝑋𝑛 =1–5) : Telomer (case 2)

42. Other case 1) If R.D.S. of initiation is the first step
2) Cationic polymerzation initiated by ionization radiation
Initiation
Termination by inhibitor
Termination by combination w/ counter ion
In Radical
Radical ∙M- can also be generated

43. 3) Very pure system ; no impurity
Then the only possible termination is
⇒ one cation is generated when one anion is generated
If ionization radiation is used for initiation ⇒ Y-=e-
; combination by counter ion

44. 5-2d-2 Validity of steady state assumption
1) Cationic polymerization is very fast
Ex)
Ri > Rt
time M+
S. S. assumption is valid only in very short period
→ In cationic polymerization, initiation is very fast!

45. ∴ possibly heterogeneous polymerization
2) Solubility?
→ initiating system & growing species can be insoluble in the rxn mixture
; salt are not soluble ①
∴ possibly heterogeneous polymerization
∵ solvents for cationic polymerization
→ Low polarity ; no rxn w/ carbocation ②
∙ Solubility also changed
∴ Rp expression in cationic polymerization is always erroneous
To get more reliable Rp, [M+] should be determined
How?
① Short-stopping of polymerization by an efficient terminating agent
② Stop-flow, rapid scan spectroscopy
insoluble
Partially insoluble
soluble
capillary
spectroscopy

46. 5-2e-2 Difficulty in interpreting rate constant
→ Most reported kp values are apparent or pseudo rate constant
⇒kpapp
Ion pair or free ion → both are possible w/ different rate constant
Free ion
Ion pair

47. acid in 1,2-dichloroethane at 20 oC where K is 2.8 x 10-7 mol L-1
Ion pair
Free ion
Some salt of carbocations can be crystallized ⇒ conc. can be obtained
% of Mf+ 99 90 62 27 9 2 1
0.3
C/K
10-2
10-1 10
102
103
104
105
For example styrene polymerization by triflic (trifluoromethanesulfonic)
acid in 1,2-dichloroethane at 20 oC where K is 2.8 x 10-7 mol L-1
at acid concentrations of 2.8x 10-5 mol (C/K = )
 91% propagation by ion pairs and 9% propagation by free ions.
Most polymerization

48. Cationic polymerization is faster than radical polymerization
∴ Rp,cat ≫ Rp,rad
Kp [L/mol-sec] kt ki
[M+] or [M∙]
Cationic
102 ~ 109
10-1 ~ 10-2
1 ~ 102
10-5
Radical
102 ~ 104
106 ~ 108
10-2 ~ 10-4
10-7 ~ 10-9

49. p-OCH3 > p-CH3 > H > p-Cl > m-Cl > m-NO2
Reactivity of monomer
→ not enough data
Vinyl ether > isobutylene > styrene, isoprene
Styrene derivatives
p-OCH3 > p-CH3 > H > p-Cl > m-Cl > m-NO2
Probably due to the e- donating effect
e- donating

50. CM and CS values Generally larger kp, lower CM
Temp.↓ CM ↓ ∵ bond cleavage effect
→ not much data for the comparison

51. The larger transfer constants are associated with transfer agents that possess a
weakly bonded negative fragment (e.g., CH3O- in CH3OH) or are readily alkylated
(CH3OΦ).

52. Ε (dielectric constant)
Effect of reaction medium
Solvent effect
in general highly polar solvent, free ion is favored over ion pair
ex)
However, it is not always true
∵ Solvent polarity↑, kp+↓
Ε (dielectric constant)
CH2Cl2
9.72
CCl4
0.12
∵ free ion character decrease

53. 5-2f-3 Counterion Effects
It is generally accepted that there is little effect of counterion on reactivity of ion pairs since the ion pairs in cationic polymerization are loose ion pairs.
However, there is essentially no experimental data to unequivocally prove this point. There is no study where polymerizations of a monomer using
different counterions have been performed under reaction conditions in
which the identities and concentrations of propagating species are well established.

54. Pseudocationic polymerization
Ex) Styrene + perchloric acid HClO4
⇒ propagation can proceeds through covalent species
kpc : rate constant for propagating end w/ covalent bond, very small value
solvent polarity↑, kpc constant or ↑

55. then there would be unimodel molecular weight distribution
⇒ Kc is faster than and
then there would be unimodel molecular weight distribution
Kc is obviously slower
∴ bimodal M.W.D
High M.W.
Low M.W.
Elution time
Ph-NO2/CH2Cl2=1/7
Ph-NO2/CH2Cl2=1/15
CH2Cl2
CH2Cl2/benzene=10/1
CH2Cl2/benzene=2/1
Rxn solvent
Due to &
Due to kpc
G.P.C. results

56. 7 criteria for living polymerization
by Quirk, poly. Int. (1992), vol.27
1) Polymerization proceeds until [M]=0
Addition of more monomer results in continuous polymerization
2) Is a linear function of conversion
∴ not a sufficient criteria
Number of polymer molecules remains constant
→ also possible when termination occurs w/o C.T.
∴ necessary but not sufficient 4)
if there is C.T. rxn, (obs) < (cal)
Narrow molecular weight distribution
ie.
※ linear plot is also possible when termination occurs w/o C.T.
conv.
Poisson M.W.D.
Block copolymer preparation
7) Quantitative chain end fuctionalization
⇒ found in many anionic polymerization, How about cationic polymerization?

57. ※ Requirement for Poisson M.W.D.
ⅰ) growth occurs by consecutive addition
ⅱ) all chain-ends are equally reactive
ⅲ) all chain-ends, active-ends are present at start
ⅳ) no chain termination or chain transfer
⇒ ki vs. kp ratio is very important
ex) J. Chem. Phys. 28, 91 (1958)
∴ narrow M.W.D. is possible when kp / ki <10
※ Narrow M.W.D. is possible for other cases such as mixture
ex)
kp/ki
P.D.I.
0.1
1.008
0.5
1.01 10
1.019
100 ?
106
1.25
Living system

58. Quasi-living carbocationic polymerization
⇒ Carbocations are so reactive that C.T. & terminations are facile
∴hard to get living system
⇒ 1980th Kennedy et al. at U. Akron
∙ Absence or reversibility of termination and/or C.T.
∙ Monomers are mostly consumed by propagation
- See p.403 examples -
Ex)
∙ The active-end is not a carbocation
∴ not very reactive
∙ The active-end is not totally covalent
∴ reactive
⇒ no termination, no C.T. ∴ pseudo living +δ -δ

59. Energetics Using Arrhenius equation
Ep for cationic polymerization ; positive but not much large < 20~25kJ/mol
Et ; except the combination w/ counter ion
all termination involves chain cleavage
Ei ; case by case
mostly involves the chain cleavage

60. If there is C.T.
→additional term
possible at higher temp.

61. 5-2i Commercial Applications of Cationic Polymerization
5-2i-1 Polyisobutylene Products
polyisobutylene, polybutene, and butyl rubber are produced by cationic polymerizations and copolymerizations of isobutylene.
Polybutenes
- very-low-molecular-weight copolymers (Mn < 3000), containing about 80%
isobutylene and 20% other butenes (mostly 1-butene)
- Applications in adhesives, caulking, sealants, lubricants, plasticizers, and
additives for motor oils and transmission fluids (for viscosity improvements).
Polyisobutylenes
Low-molecular-weight (up to Mv 5–10 x 104): viscous liquids to tacky
semisolids andare used for sealant and caulking applications.
High-molecular-weight (Mv > 105) : rubbery solids used to make uncured
(uncrosslinked) rubber products and as impact modifiers of thermoplastics.
Polymerization at 40 to 10 oC with AlCl3 (BF3 or TiCl4) produces the lower-molecular-weight products.
Polymerization at -100 to -90 oC produce the high molecular-weight polyisobutylenes

62. Butyl rubber (BR)
copolymer of isobutylene with small amounts of isoprene
Produced by cationic polymerization using aluminum chloride
about 1 billion pounds are produced annually in the United States
Procedure (continuous process)
1) Isobutylene and isoprene are purified and then mixed together in methyl
chloride solution.
2) The initiation system is produced by passing methyl chloride through beds of
aluminum chloride at oC followed by dilution with methyl chloride
and the addition of the initiator (protogen or cationogen).
3) The initiation and monomer solutions are chilled separately to -100 to -90 oC
by using boiling ethylene and propene or propane as heat exchangers.
4) The mixtures are injected rapidly and continuously into the reactor,
then polymerization occurs almost instantaneously with the polymer
precipitating as a fine slurry in methyl chloride.
5) The slurry overflows into a flash tank containing steam and hot water, and
small amounts of zinc or aluminum stearate (to control the particle size of the
butyl rubber latex) and antioxidant are added.
Solvent and unreacted monomers are vaporized and pass into a recovery system.
6) The aqueous slurry of butyl rubber passes into a stripping tank under vacuum
to remove residual amounts of methyl chloride and unreacted monomer.
The stripped slurry is then pumped to a series of drying extruders
to dewater the product and compressed into bales ready for shipment.

64. 5.3 Anionic Polymerization of the Carbon-Carbon Double Bond
Anionic Polymerization → similar to cationic polymerization
Difference from cationic polymerization
1) Rate constant difference between is very large and
in cationic
2) is always positive
∴ Temp↑ Rp↑
in cationic or
3) Solvent for anionic polymerization
→ Aliphatic hydrocarbon, aromatic hydrocarbon, ether.
→ Due to the strong nucleophilicity of carbanion, halogenated solvent, ketone, esters can not be used.
※ in cationic polymerization, halogenated solvent can be used (except 3o carbon)
4) Termination by transfer of a positive fragment such as H+
not very different

65. Reactions of carbonion with
1) Air
2) Acid
where H-A; ROH, RCOOH, RSH, RCH2(CO)R, PhCH3, C2H2, CH2=C=CH2
→ depend on the pKa of ( )
3) Carbonyl group
4) Halogenated compounds

66. Monomer requirements for anionic polymerization
⇒ ∙ carbanion should be stabilized
∙ no side reaction
1) Y = e--withdrawing or e--delocalizing substituent
= -CH=CH2, -Ph, -CO2R, -CN, -SO3R, -COR, -NO2
Absence of acidic proton
-COOH, -OH, -NH2, -C≡CN can not be used
Absence of electrophilic substituent which react with anionic chain end
-CN, -SO-, -SO2-, -C(O)R, -COOR, -NO2
∴ Possible monomers ( Table 3.1 p 200)

69. Initiators
※ To initiate, the initiator should be more basic than the propagating chain end.

70. 5-3a Initiation 5-3a-1 Nucleophilic initiator (basic initiator)
→ NaNH2, LiN(C2H5)2, alkoxide, hydroxide, cyanide, organometallic compounds (BuLi)

71. 5-3a-2 Electron transfer initiator
i) Naphthalene anion-radical transfer
Very fast
<1% radical polymerization
Rate constant ( L mol-1s-1 )
>99% anionic polymerization

72. ↓dimerization ↓polymerization ⅱ) Lithium in liquid ammonia
ⅲ) Ionizing radiation ∙∙
stable
↓dimerization
↓polymerization

73. 5-3b Termination 5-3b-1 Polymerizations without Termination
⇒ possible for a certain degree because termination by combination
of the anion with a metal counterion does not take place.
Ex) anionic polymerizations of nonpolar monomers such as styrene and 1,3-butadiene
5-3b-2 Termination by Impurities and Deliberately Added Transfer Agents

74. 5-3b-3 Spontaneous Termination
hydride elimination
∵ hydride elimination is possible even in most stable styrene
The order of stability of polystyryl carbanions : K > Na > Li.
Stability according to polarity of solvent
Polystyrly carbanion : less stable at higher temp. in polar solvent THF, DME.

75. 5-3b-4 Termination and Side Reactions of Polar Monomers; :
such as acrylates

76. Desirable anionic polymerization of acryl monomer
Other side reactions

77. 5-3d Kinetics of Living Polymerization
5-3d-1 Polymerization Rate
In cationic
where [M-] is the total concentration of all types of living anionic propagating centers (free ions and ion pairs).
Free ion
Ion pair
In Radical
Anionic kpapp values :
10–100-fold lower than in radical polymerization in hydrocarbon solvents,
10–100-fold higher for polymerizations in ether solvents.
[M∙] = 10-9 – 10-7 M
[M-] = 10-4 – 10-2 M
Thus anionic polymerization rates are much higher than radical rates
based only on the concentrations of propagating species.

78. In cationic
In Radical

79. 5-3d-2 Effects of Reaction Media
⇒ The increase in kpapp with increased solvating power
∵ the increased fraction of free ion
⇒ DME > THF
∵ DME have two ether bond in a same molecule
→ increased solvating power

80. 5-3d-2-a Evaluation of Individual Propagation Rate Constants for Free Ions and Ion Pairs.
where P- is free propagating anion and P-(C+) is the ion pair
because
where [M-] is the total concentration of all types of living anionic propagating centers (free ions and ion pairs).

81. The two propagating species are in equilibrium
If there is no source of either ion other than P-(C+)
The extent of dissociation is small under most conditions, then [M-]  [P-(C+)]
because
[M-] = [P-] + [P-(C+)]
because

82. If polymerizations in the presence of excess counterion by adding a
strongly dissociating salt (e.g., NaB4 to supply excess Na+).
Then the concentration of free ions, depressed by the common ion effect, is given by
because
[M-]  [P-(C+)]
When the added salt is strongly dissociated and the ion pairs slightly dissociated, the counterion concentration is very close to that of the added salt [CZ]:

83. Polymerization of styrene by sodium naphthalene in 3-methyltetrahydrofuran at 20 0C
can be obtained

84. Polymerization of styrene by sodium naphthalene in 3-methyltetrahydrofuran at 20 0C in the presence of sodium tetraphenylborate.
can be obtained

85. Styrene 5-3d-2-b Reactivity in Anionic Polymerization. [M-]  [P-(C+)]
In THF  dissocation : ion pair + free ion
Li : 1.5% of free ions among the all propagating centers of 10-3 M
calculated by K in THF
Then, majority propagation by free ion, and only 10% by ion pair
In Dioxane:  no dissocation , estimated by conductivity
only ion pairs

86. The K values
> > > x 10-7
Lithium > sodium > potassium > cesium counterions
K increase with the increase of the solvation power
 Smaller Li+ ion solvated better than Larger Cs+ in THF ↑
(Li > Cs)
Ion pair : solvent-separated + contact ion pairs
The fraction of solvent-separated ion pairs increases with increasing solvation
of the counterion.
Solvent-separated ion pairs are much more reactive than contact ion pairs (Sec. 5-3d-4).

87. In Dioxane:
 no dissocation : only ion pairs ↑
(Li < Cs)
bond strength (carbanion center and counterion)  , from Li to Cs
However, the effect of increasing counterion size levels off after k is approximately the same for potassium, rubidium, and cesium.

88. Methyl methacrylate (MMA)
the absence of solvation by THF for MMA polymerization due to the presence of intramolecular solvation.
low dissociation constant (K < 10-9)
Therefore, kp = 1 for lithium and 30–33 for the larger alkali metal in THF at -98 oC
poly(2-vinylpyridine) ion pairs: electron donation of N
the decrease in dissociation constant, K, with decreasing size of counterion in THF.
K = 1.1 x > x 10-10
Cs > Na

89. 5-3d-3 Degree of Polymerization
propagating species formed from sodium naphthalenes
(e.g., alkyllithium)

90. 5-3d-4 Energetics: Solvent-Separated and Contact Ion Pairs
anionic polymerization of styrene
; especially with regard to the multiplicity of propagating species
Ionic species aggregate
CIP : contact ion polar
SSIP : solvent seperated ion pair
In non polar solvent, the propagating center
In polar solvent, the propagating center
: H.C.
Benzene
toluene

91. Styrene propagation in H.C. solvent (nonpolar)
See next page table 7.1
Why?
⇒ aggregation
-Counter ion dependence of kp,obs
∵ kd increases increasing cation size
⇒ total chain end concentration =

93. Diene polymerization in non polar(H.C.) solvent
⇒ See table 7.1 for Isoprene & Butadiene case
kinetic order 0.17~0.5 case by case

94. Styrene propagation in polar solvent (THF, dioxane, DME, etc.)
Presence of free ion is deduced by conductance & common ion effect
Evidence for CIP, SSIP comes from JACS, 88, 307 (1996)
⇒ UV-Vis spectrum changed with temp., solvent, and M+
not affected by common ion or dilution
interpreted in terms of
◈ For M=Na
exothermic
ΔHo=-7.6 kcal/mol ΔSo<0
∴ T↑, K↓ [SSIP]↓

95. i.e. Li+ is a strong acid and is strongly solvated
◈ % SSIP↑ in the order Bu4N~C < Na < Li follows order of Lewis acidity
i.e. Li+ is a strong acid and is strongly solvated
% SSIP↑ as solvent strength increases
DME ≥ THF > dioxane
ex)∙J.A.C.S., 103, 5657, 1983
studied 13C-NMR of Ph2-CHM+ in THF
SSIP for Li
Mixture of CIP/SSIP for Na
CIP for K, Cs, Rb
∙J.P.S., 69, 612 (1965)
for low free ion conc. α≪1
Accept the unpaired e-
↑ ↑
SSIP+SIP free ion

96. ◈

97. : Li > Na > K > Rb > Cs
k – is independent of M+, ∵ free ion
slope change reflects kd1/2 ( or K1/2 in the text ) , Li is most strongly solvated, kd is highest
⇒ highest % free ions for Li
Dioxane : less polar solvent
∴ reactivity is proportional to the bond strength
⇒ same as non polar solvent
Cs > K > Na > Li

98. If NaBPh4 is added to PSNa
⇒ The increase in kpapp with increased solvating power
∵ the increased fraction of free ion
DME > THF
∵ DME have two ether bond in a same molecule
→ increased solvating power
If NaBPh4 is added to PSNa
kpapp changes from 2100 to 140 L mol-1 s-1
∵ common ion effect
reduce the conc. of free ion!

99. Temperature dependence of k -
ln k - vs. 1/T is linear
k – is independent of solvent
⇒ Eur. Polym. J., 11, 119 (1975)

100. k± shows a nonlinear dependence on T k± depends on solvent
However,
k± shows a nonlinear dependence on T
k± depends on solvent
Explanation
⇒Conc. Of SSIP
⇒Conc. Of CIP

101. CIP
THF
3Me-THF
SSIP
⇒ p.431 odian

102. PS M exist as multiple species in polar solvent ;
In summary
PS M exist as multiple species in polar solvent ;
each contributes to propagation
The relative populations depend on T, M+, solvent
⇒ k - = 10(kS) = 1000(kC)
If the equilibriums are faster than,
kC, kS, k -, then
Combination of kC&kS

103. 5-3d-5 Association Phenomena in Alkyllithium
For styrene polymerization by n-butyllithium in aromatic solvents, the initiation and propagation rates are proportional to only the 1/6- and 1/2-powers of n-butyllithium concentration, respectively.
The macrocyclic crown ethers such as 18 crown-6 (XXIXa) and cryptands such as cryptand (XXIXb) are extremely powerful for breaking up association of organolithium compounds.
to greatly increase the concentration of free-ion propagating species, resulting
in very large rate increases

104. Crown Ether effect of MMA anionic polymerization
DB-18-CE-6
∵ Chelation increases the effective size of the counter ion
Temp. (oC)
C.E./I Mn
Mw/Mn 25 1
10500
1.40 2
1.03
8500
1.20
1.05
→ large effective
counter ion
radius

105. Kinetics of polymerization with termination
⇒ Ri : the rate of initiation
Propagation
Chain transfer to solvent
Chain transfer to adventitious water , also termination
If there is steady state,
↘Conc. Of anionic propagating chain center

106. 5-4 BLOCK AND OTHER POLYMER ARCHITECTURES
5-4a Sequential Monomer Addition
Block copolymer
ex) Synthesis of PS-PMMA block copolymer ∴
∴ Sequence is very important
※ For Styrene-Isoprene, Styrene-butadiene Sequence is not important

107. 5-4b Telechelic (End-Functionalized) Polymers
Crossover from one carbanion to another occurs only when the new carbanion is comparable or higher in stability than the original carbanion.
Poly(methyl methacrylate) carbanion is more stable than polystryrene carbanion. Carbanion stability can be estimated from the pKa of the conjugate acids of model carbanions.
Toluene and ethyl acetate have pKa values of 43 and 30, in line with the higher stability of the PMMA carbanion.
5-4b Telechelic (End-Functionalized) Polymers
Containing one or more end functional groups

108. amine-terminated telechelic polymers
⟹ Monofunctional telechelic polymers containing OH, NH2, COOH groups
They can be used to obtain diblock copolymers.
styrene–isobutylene–styrene triblock polymer.
diethylaluminum chloride styrene 

109. 5-4c Coupling Reactions
Living anionic polymers and block copolymers can be linked by coupling reactions.
the synthesis of star (multiarmed) polymers
CH3SiCl3, (ClCH2)4, and 1,2,4,5-tetrachloromethylbenzene also can be used
3-arm star with one polyisoprenyl (PI) and two polystyryl (PS) branches

110. Using 1,3,5-tris(1-phenylethenyl)benzene to make tristar and Miktostar polymers

111. 5-4d Transformation Reactions
The anionic to cationic transformation
The anionic-to-radical transformation
⇒ Limitation:
A∙B both can propagate Anionic/cationic or anionic/radical polymerization

112. 5-6 CARBONYL POLYMERIZATION
⇒ Tc is very low except formaldehyde
⇒ ∵
ΔS is approximately the same

113. ⅰ) Formaldehyde initiator
→ R- M+, RO- M+, RCOO-M+, amine, pyridine
Initiation
Propagation
Termination
ⅱ) Other carbonyl monomer other than HCHO
⇒ Stronger bases such as alkali metal alkyls & alkoxide are the initiator ◈
1) Inductive effect : destabilize the propagating anion
2) Steric effect
◈ X=F,Cl
⇒ stabilize the propagating anion
∴ Tc is higher than RCHO (Table 5.3)

114. Cationic polymerization
initiator : protonic acid (HCl, CH3CO2H), Lewis acid
Initiation
Propagation
Termination

115. ⇒ competing side reactions
ⅰ) cyclotrimerization (6-membered ring)
ⅱ) Acetal formation
⇒ both can be minimized by polymerization at low temperature

116. Hydrogen-Transfer polymerization
Initiator : sodium, organolithium, alkoxide
→strong base
⇒ yield is not very high
∵ possible side rxns

117. Radical polymerization of carbonyl monomer
⇒ Generally not possible
ⅰ) : polar compound
∴ not prone to attack by a radical
ⅱ) most radicals are produced at temperatures above Tc of carbonyl monomer
Several cases for radical poly. of carbonyl monomers
ⅰ) : Trifluoroacetaldehyde w/
at 22℃
ⅱ) using trialkylboron-oxygen redox initiator
at -78℃
∴less polar system! +δ -δ
Less e- negative

118. End-capping
Polyacetals from carbonyl monomers are unstable at ambient temperature
∵ low Tc ⇒ practical application is limited
※ end-capping or end-blocking
ex)
⇒ Reactive site (anion or cation) does not from at the chain end,
then no depolymerization at Tc
Polyoxymethylene (POM, Delrinⓡ) is commercial polymer
150 million pound / year
: highly crystalline 60~77%
Tm=175℃ (ease of packing ∵flexible)
higher than PEO(~60℃), PE(~140℃)
∵ higher polarity

119. Monomers w/ two different polymerizable groups∵
both parts are sterically hindered
⇒ radical : homopolymer
anionic : copolymer
Hydrogen transfer polymerization
radical, cationic, or anionic ?
No reactivity Na
RLi
Vinyl group anionic polymerization is impossible
-NH2 acidic

120. How?
∴ ⅰ) hydrogen transfer
ⅱ) active site is monomer anion
∴ While some units are generated
depending on solvent, temp., concentration, initiator
There is some chances
→initiation
propagation ↑
Activatied monomer

121. Radical, cationic, anionic
n R-N=C=O
Polyisocyanate
Nylon1
liquid crystalline polymer ∵rigid backbone
→ anionically polymerized using
low Tc
∴ predominant rxn at RT
Radical, cationic, anionic
1) Ionic poly. : at low temp. w/ low activation energy
Radical poly. : 50℃<
2) Ionic poly. : sensitive to solvent, counter ion, solvent polarity
∵solvation ability
Radical poly. : insensitive
∵ radical inself is organic
no solubility problem
Polymerization through N=C bonds
Through anionic polymerization