1.  Free radical Initiation Processes
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1. Free radical Initiation Processes. 2. Cationically Initiated Processes. 3. Anionically Initiated Processes. 4. Group Transfer Polymerization. 5. Coordination Polymerization. Chap 9. Chain-growth Polymerization. Chain-Growth Polymerization (Addition) Processes.

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  • 2. Cationically Initiated Processes

  • 3. Anionically Initiated Processes

  • 4. Group Transfer Polymerization

  • 5. Coordination Polymerization

Chap 9. Chain-growth Polymerization

Chain-Growth Polymerization (Addition) Processes

Chain-Growth Polymerization

  • 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.

Step-Growth Polymerization

  • Molecular weight increases steadily.

  • High molecular weight polymers are found at the end.

  • Long reaction time needs to synthesize high conversion and high molecular weight.

Bond Energy= 46 kcal/mole

Heat (60ºC)

UV kd

Primary radical


Chain Growth Polymerization

(1) Initiation

kd : Initiator decomposition rate constant

: 10-4 ~ 10-6 L/mole sec

Unstable radical

Chain Growth Polymerization

(2) Propagation

(Repetition of similar reaction)

kp : 102 ~ 104 L/mole sec (much faster than step-growth polymerization)

Chain Growth Polymerization

(3) Termination

(a) Coupling or combination

Chain Growth Polymerization

(3) Termination

(b) Disproportionation


106 ~ 108 L/mole sec

Chain Growth Polymerization

(4) Chain Transfer

Physical chain length

Monomer, Polymer, Solvent or Chain transfer agent

Kinetic chain length

Chain Growth Polymerization

  • Kinetic Chain Length :

  • kinetic chain length υ 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 # 4000 Disproportionation

  • υ =4,000/4 =1,000

  • Determined by steps 1, 2, 3. (Initiation, propagation, and termination)

  • (No chain transfer)

  • Physical Chain Length :

  • This condition contains Step 1, 2, 3, 4.



  • Non-Polymerization Reaction

  • Peroxide induced Bromination of Toluene

  • 1) Initiation

  • Two types of reaction

  •  R-O-O-R 2RO• (1)

  •  R-O• + Br2 ROBr + Br• (2)

  •  R-O• + ФCH3 ROH + ФCH2•(3)

  • Two radicals and two kinetic chains are formed by decomposition of

  • each ROOR molecules

  • Kinetic Chain Reaction

    Kinetic Chain Reaction

    • 2) Propagation

    •  Br• + ФCH3 HBr + ФCH2 (4)

    •  ФCH2• + Br2 ФCH2Br + Br • (5)

    • Two special features

       The number of active species is fixed.

  •  Same reactions are repeated during the kinetic chain reaction.

  • Kinetic Chain Reaction

    • 3) Termination

    •  2 Br• Br2

    •  2ФCH2• ФCH2 CH2Ф

    •  ФCH2• + Br • ФCH2Br + Br •

    • Net Effect of Kinetic Chain Reaction:

    • One ROOR molecule can cause formation of Br2, CH2CH2, CH2Br,HBr, ‥.

    Kinetic Chain Reaction

    • Comparison between Chain Polymerization & Chain Reaction




    Chain reaction Ri= Rt

    Reaction Rate

    Steady state


    Induction period

    In proportion to the O2 concentration

    Kinetic Chain Reaction

    • In the case of Chain reaction, there are induction periods, due to the existence of inhibitor.

    • When an active center is formed, the reaction rate would be faster and then go to steady state.

    • The whole reaction rate is reaching a plateau region.

    • After that, reaction rate decreases due to a loss of monomers or initiators.

    • 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

    • Comparison Free Radical Reaction &Ionic Reaction

    • - Ionic Initiation – multiple bond addition,ring opening polymerization

    • - Radical Initiation – Ring-opening polymerization is not initiated.

    For the cationic initiation, it will not be free radical.



    Because of resonance stability

    Kinetic Chain Reaction

    • Comparison between Free Radical Reaction &Ionic Reaction

    Kinetic Chain Reaction

    • Comparison between Free Radical Reaction & Termination Step of Ionic Reaction

    • A) Free Radical Termination

    Two molecules involved

    = bimolecular reaction

    Kinetic Chain Reaction

    • B) Cationic Termination

    Anionic capture is similar to combination offree radical reaction.

    But, this reaction can’t include increasing of MW because of unimolecular reaction

    Kinetic Chain Reaction

    • The proton release is similar to disproportination offree radical..

    • But, one chain joins in the reaction unimolecular reaction

    • C) Anionic Termination

    Kinetic Chain Reaction

    • Free Radical Initiated Polymerization of Unsaturated monomers

    • Kinetic Scheme

    • Initiation

    • Two step sequence-Both enter into overall rate

    • Initiator decomposition

    • I2 2I

    • 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

  • kd


    Primary radical species

    Generally, 0.5 << f << 1

    Kinetic Chain Reaction

    • A.Cage Effect –primary recombination

    • Initiator fragments surrounded by restricting cage of solvent

      • Ex)

      • (acetyl peroxide)

    Kinetic Chain Reaction

    • I) Recombination possible I2 2I

    • 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

    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 obtainedhalf molecules were wasted.)



    I + M


















    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

    C. Reaction Rate

    If [M] is representative for the concentration of chain radical,

    That is , M = IM

    or = I [M]

    f  1 Riis unrelated with [M]


    f < 1 Ri is related with [M]

    [M] , f

    [I2] , f due to induced decomposition

    by convention, tworadical formation.

    Kinetic Chain Reaction

    • D. Initiator

    • - containing compounds.

    Acetyl peroxide 80~100C

    Benzoyl peroxide 80~100C

    • Cumyl peroxide 120~140C

    Kinetic Chain Reaction

    • t-butyl peroxide

    • Hydroperoxides, cumyl or t-butyl

    • 80~100C


    • AIBN 2,2 azobisisobutyronitrile









    Kinetic Chain Reaction

    • Propagation

  • Termination

  • By convention

    Since 2 radical elimination

    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)

    Kinetic Chain Reaction

    [M]elimination methods

    Steady-State Assumption

    Radical concentration increases at the start, comes to steady state simultaneously

    and thenreaction rate change becomes 0. (active centers created and destroyed at the same time)

    Ri = Rt

    MMA using BPO


    Vinyl Acetate using AIBN




    Kinetic Chain Reaction

    Mostly in case of f<1system → [I2]1/2 (Square Root Dependence of [I2])

    ※ Odian Fig. 3-4





    + N2


    + BPO +




    Kinetic Chain Reaction

    In case f < 1, but SRD is not applicable,

    Because f is‘dependent’ on [M]


    Due to induced decomposition of toluene + [I2]

    Kinetic Chain Length (KCL)

    At S-S assumption

    (1) Disproportionation

    Knowing that

    (2) Coupling or combination

    Kinetic Chain Length (KCL)

    (3) Both (1)+(2)

    Kinetic Chain Length (KCL)

    Degree of Polymerization

    • The more concentration of monomer,

    • The less concentration of initiator,

    Monomer consumption rate

    polymer formation rate

    (1) Dispropotionation

    (2) Coupling

    Kinetic Chain Length (KCL)

    (3) Dispropotionation& Coupling

    Polymer formation rate

    Monomer consumption rate

    Kinetic Chain Length (KCL)

    • From (1),(2),(3)

    • In case of noChain transfer, and valid S-S assumption

    Chain Transfer

    • M + XY MX + Y

    • Chain transfer agent

    • If Chain transfer occurs Rpisunchangable buthas an effect on DPn

    • (∵ Since [Y] instead of Rp=kp[M][M] )


    • (1) Chain transfer occurs by solvents or additives

    • In this case,Highchain transfer coefficient.

    • (2) Transfer occurs by monomer or polymer

    Chain Transfer

    Inhibitor and Retarder

    • Inhibitor

  • 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

    Chain Transfer


    See Odian P.235


    From the slope of a graph

    Chain transfer coefficient ‘Cs’


    Temperature Dependence of Rp and DPn

    • Assume : no chain transfer

    Temperature Dependence of Rp and DPn

    • slope of lnRp/T is ( + )

    • as T  lnRp

    • but Rate of Increase  as d lnRp/dT 

    Ceiling Temperature Polymer-Depolymerization Equilibria

    ㆍCeiling Temperature

    Polymerization and Depolymerization are in equilibrium

    ΔGp = ΔHp – TΔSp

    ΔHp : Heatof polymerization

    ΔSp : Molecular arrangement changes between monomer andpolymer

    At eq. State ΔGp=0

    Monomers can no longer be persuaded to form polymers by chain

    polymerizationabove a certain temperature.ceiling Temperature(Tc)

    Rate Eq. of Polymerization Reactions

    at Depolymerization prominent Temperature


    M Tc

    Ceiling Temperature Polymer-Depolymerization Equilibria





    : No reaction above Tc

    Stable blow Tc


    kp[M]- kdp





    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.

    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, ktdrop off in reaction progress)

    → Autoaccerelation effect

    Trommsdorff Effect or Gel Effect

    one would expect ξ  as t Butξ  as [[M0] 



    • autoacceleratioan


    as [M0] drastic in .