1. Chap 10. Chain-growth Polymerization
Chain-Growth Polymerization (Addition) Processes
1. Free radical Initiation Processes
2. Cationically Initiated Processes
3. Anionically Initiated Processes
4. Group Transfer Polymerization
5. Coordination Polymerization

2. Chain Growth Polymerization
Characteristics
Only growth reaction adds repeating units one at a time to the chain
Monomer concentration decreases steadily throughout the reaction
High Molecular weight polymer is formed at once; polymer molecular
weight changes little throughout the reaction.
Long reaction times give high yields but affect molecular weight little.
Reaction mixture contains only monomer, high polymer, and about 10-8
part of growing chains.

3. Chain Growth Polymerization
(ⅰ) Initiation
kd : Initiator decomposition rate constant
: 10-4 ~ 10-6 L/mole sec
Heat (60ºC)
UV kd
Primary radical
AIBN
Bond Energy = 46 kcal/mole
Unstable radical

4. (ⅱ) Propagation
kp : 102 ~ 104 L/mole sec

5. (ⅲ) Termination
(a) Coupling or combination

6. (b) Disproportionation
kt=ktc+ktd
106 ~ 108 L/mole sec

7. Chain Growth Polymerization
Kinetic Chain Length :
kinetic chain length v of a radical chain polymerization is defined as the average number of monomer molecules consumed (polymerized) per each radical, which initiates a polymer chain.
ex) Monomer # Disproportionation
ν=4,000/4 =1,000
Decided by step 1,2,3.
Physical Chain Length :
This condition contains Step 1,2,3,4
Radical
1,2,3,4

8. Kinetic Chain Reaction
Non-Polymerization Reaction
Peroxide induced Bromination of Toluene
1) Initiation
Two types of reaction
 R-O-O-R RO• (1)
 R-O• + Br ROBr + Br• (2)
 R-O• + ФCH ROH + ФCH2• (3)
Tow radicals and tow kinetic chains formed by decomposition of
each ROOR molecules

9. Kinetic Chain Reaction
2) Propagation
 Br• + ФCH HBr + ФCH2 (4)
 ФCH2• + Br ФCH2Br + Br • (5)
Two special features
Number of active species is fixed
 During kinetic chain reaction, same reactions was repeated

10. Kinetic Chain Reaction
3) Termination
 2 Br• Br2
 2ФCH2• ФCH2 CH2Ф
 ФCH2• + Br • ФCH2Br + Br •
NET EFFECT OF KINETIC Chain rexn:
One ROOR molecule can cause formation of Br2, CH2CH2, CH2Br,HBr, ‥.

11. Kinetic Chain Reaction
Comparison Chain Polymerization & Chain Reaction
Init.
propagation
termination
Chain reaction Ri == Rt
Reaction Rate
Steady state
Time
Induction period
In proportion to the O2 concentration

12. Polymer of high DPn found easily in early reaction Linear Step-Growth:
In case of Chain reaction, there are mainly induction periods, due to the inhibitor. If an active center is formed, the reaction rate accelerate and then come to steady state. The whole reaction rate is reaching plateau region.
Linear Chain-Growth:
Polymer of high DPn found easily in early reaction
Linear Step-Growth:
high extent of reaction value required to obtain high DPn
Kinetic Chain Reaction

13. Kinetic Chain Reaction
Comparison Free Radical Reaction & Ionic Reaction
- Ionic Initiation – multiple bond addition, ring opening polymerization
- Radical Initiation – Ring-opening polymerization has not initiation reaction.
Kinetic Chain Reaction

14. Kinetic Chain Reaction
Comparison Free Radical Reaction & Ionic Reaction

15. Kinetic Chain Reaction
A) Free Radical Termination
Kinetic Chain Reaction
Comparison Free Radical Reaction & Termination Step of Ionic Reaction
Two molecules involved
= bimolecular reaction

16. Kinetic Chain Reaction
B) Cationic Termination
Kinetic Chain Reaction
Anionic capture is analogous to combination of free radical reaction.
But, this reaction can’t include increasing of MW because of unimolecular reaction

17. Kinetic Chain Reaction
The proton release is similar to disproportion of free radical..
But, one chain join in the reaction unimolecular reaction
Kinetic Chain Reaction

18. Kinetic Chain Reaction

19. Kinetic Chain Reaction
Free Radical Initiated Polymerization of Unsaturated monomers
Kinetic Scheme
Initiation
Two step sequence-Both enter into overall rate
Initiator decomposition
I I
2. Addition of Initiator fragment to the monomer, Initiation of Chain growth.
I+M IM
The efficiency of Initiator - Determined by competition of desired reaction and side reaction
Primary radical species
Generally, << f << 1 kd ki
Kinetic Chain Reaction

20. Kinetic Chain Reaction
A.Cage Effect –primary recombination
Initiator fragments surrounded by restricting cage of solvent
Ex)
(acetyl peroxide)
Kinetic Chain Reaction

21. Kinetic Chain Reaction
I) Recombination possible I I
II) If elimination reaction occurs while the free radical in-cage,
Formation of stable molecules due to Radical combination.
And formation of Inactive Species.
Kinetic Chain Reaction

22. Kinetic Chain Reaction
B. Induced Decomposition –Secondary combination
I) Through Radical attack on peroxide molecules
R + R-O-O-R RH + ROOR R=O + RO
Finally, R + ROOR ROR+ RO
Total number of radical does not change, but among them half molecules were wasted.
II) Chain Transfer to Solvent
(In this case, since just one radical was obtained half molecules were wasted.)
Kinetic Chain Reaction

23. Kinetic Chain Reaction
III) Reaction with Chain Radical
Since not all Molecules participate in the initiation → Efficiency factor
f: Initiator Efficiency
= mole fraction of initiator fragments that actually initiate polymer chains.
0.5 < f < 1.0
Kinetic Chain Reaction

24. Kinetic Chain Reaction
C. Reaction Rate
If [M] is representative for the concentration of chain radical,
That is , M = IM
or = I M
f  1 Ri is unrelated with [M]
f=[M]
f < 1 Ri is related with [M]
[M] , f
[I2] , f due to induced decomposition
by convention, two radical formation.

25. Kinetic Chain Reaction
D. Initiator
- containing compounds.
Acetyl peroxide, or benzoyl peroxide 80~100C
Alkyl peroxide, cumyl or t-butyl peroxide
120~140C

26. Kinetic Chain Reaction
Hydroperoxides, cumyl or t-butyl
80~100C
50~70C
AIBN 2,2 azobisisobutyronitrile

27. Kinetic Chain Reaction
Propagation
Termination M . k tc td
By convention
Since 2 radical elimination

28. Kinetic Chain Reaction
Overall Rate of Polymerzation
Radical concentration
Difficulty of measurement, low concentration. (~10-8molar)
Thus it is impractical using this therm.
[M] elimination is desirable.
(# of propagation step >>> # of initiation step)

29. Kinetic Chain Reaction
[M] elimination methods
Steady-State Assumption
Radical concentration increases at the start, comes to steady state simutaneously.
and then reaction rate change becomes 0. (active centers created and destroyed at the same time)
Ri = Rt

30. Kinetic Chain Reaction
Mostly in case of f<1 system → [I2]1/2 (Square Root Dependence of [I2])
※ Odian Fig. 3-4
MMA using BPO
Vinyl Acetate using AIBN Rp
[I2]1/2
BPO
-CO2 2
300C
+ N2
Azobisisobutyronitrile

31. Kinetic Chain Reaction
In case f < 1, but SRD is not applicable,
Because f is ‘dependent’ on [M]
Why?
Due to induced decomposition of toluene + [I2]

32. Kinetic Chain Length (KCL)
At S-S assumption
(1) Disproportionation
Knowing that
(2) Coupling or combination

33. Kinetic Chain Length (KCL)
(3) Both (1)+(2)

34. Kinetic Chain Length (KCL)
Degree of Polymerization
The more concentration of monomer, DP
The less concentration of initiator, DP
Monomer consumption rate
polymer formation rate
(1) Dispropotionation
(2) Coupling

35. Kinetic Chain Length (KCL)
(3) Dispropotionation & Coupling
Kinetic Chain Length (KCL)
Polymer formation rate
Monomer consumption rate

36. Kinetic Chain Length (KCL)
From (1),(2),(3)
In case of no Chain transfer, and valid S-S assumption

37. Chain Transfer M + XY MX + Y Chain transfer agent
If Chain transfer occurs Rp is unchangable but has an effect on DPn
(∵ Since [Y] instead of Rp=kp[M][M] )
ex)
(1) Chain transfer occurs by solvents or additives
In this case, High chain transfer coefficient.
(2) Transfer occurs by monomer or polymer

38. Chain Transfer Inhibitor and Retarder Inhibitor Retarder
When Y take part in chain opening reaction, polymer moves from one site to another.
In this case, hydroquinone etc. are used as inhibitor.
Retarder
When the reactivity of Y is low, controlling the MW of the monomer including
these two materials, Mercaptan etc. are used as Retarder.
Like this, when chain transfer condition arises

39. Chain Transfer 1 See Odian P.235 DPn From the slope of a graph
Chain transfer codfficient ‘Cs’

40. Temperature Dependence of Rp and DPn
Assume : no chain transfer

41. Temperature Dependence of Rp and DPn
slope of lnRp/T is ( + )
as T  lnRp 
but Rate of Increase  as d lnRp/dT 

42. Temperature Dependence of Rp and DPn

43. Ceiling Temperature Polymer-Depolymerization Equilibria
Polymerization and Depolymerization are in equilibrium
ΔGp = ΔHp – TΔSp
ΔHp : Heat of polymerization
ΔSp : Molecular arrangement changes between monomer and polymer
At eq. State ΔGp=0
Monomers can no longer be persuaded to form polymers by chain polymerisation above a certain temperature ceiling Temperature(Tc)

44. Rate Eq. of Polymerization Reactions at Depolymerization prominent Temperature.
If,
Eq.
M Tc

45. Ceiling Temperature Polymer-Depolymerization Equilibriak
sec-1
kdp
kp[M]
kp[M]- kdp Tc
: No reaction above Tc
Stable blow Tc
300
400
500 Tc

46. Ceiling Temperature Polymer-Depolymerization Equilibria
※Odian Fig 3-18
Entropy changes for all polymers are not so different.
Sp= Sp- Sm (–) value of Sp is higher
Hp= Hp- Hm if (–) , exothermic.

47. Trommsdorff Effect or Gel Effect
The increasing viscosity limits the rate of termination because of diffusional limitations
restricted mobility of polymer radical
kp ( relative to [M] )
( ∵ kp const. in reaction progress, kt drop off in reaction progress )
→ Autoaccerelation effect

48. Trommsdorff Effect or Gel Effect
 one would expect ξ  as t  But ξ  as [M0]   t
80%
60%
40%
10%
autoacceleratioan
as [M0] drastic in .