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Chain Growth Polymerization

Submitted To : Dr. S.M.Mamun Kabir�

Submitted by :

Md. Al-Islam

Ulysses Arzon Roy

Anik Islam

Sazid Hossain

Zakaria Hossain Arnob

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Reference :

Advance Polymer Chemistry

Dr. S.M.Mamun Kabir

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Polymerization

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Chain Growth Step Growth

Polymerization Polymerization

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What is Chain Growth Polymerization

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Chain growth polymerization is a polymerization

Technique where unsaturated monomer molecules

add onto the active site of a growing polymer chain

one at a time.

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Key Factors of chain growth polymerization

  • Monomers
  • Initiator

Characteristics of chain growth polymerization

  • Adds one repeating unit at a time
  • Decreases concentration steadily
  • High molecular weight forms at once
  • Molecular weight changes a little through the reaction

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Types of chain growth polymerization

  • Free Radical Polymerization
  • Ionic Polymerization

# Anionic Polymerization

# Cationic Polymerization

  • Ring Opening Polymerization
  • Coordination Polymerization

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Free Radical Polymerization

“A Method of polymerization by which a polymer

forms by the successive addition of radical building

blocks”

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There are three steps of Free Radical Polymerization

Propagation

Termination

Initiation

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Initiation

  • One or two radicals are created from the initiating molecules
  • Radicals are transferred from initiator to the monomer unit

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Propagation

  • Free radical attacks a monomer and uses one electron from the pi bond form a stable bond with Carbon atom
  • The other electron returns to the Carbon atom turning the whole molecule into another radical

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  • This process continues and keeps adding to the growing chain one after another.

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  • It lasts till the chain growth is stopped by sheer termination or till there is no further monomer left to attack.

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Termination

Occur between two reactive radicals and of two

Types

Combination

  • Two chains simply couple into one long chain

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Disproportion

  • A hydrogen atom from one chain end is abstracted to another

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  • Producing one saturated group and another unsaturated group

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Chain Transfer Reaction

What is chain transfer reaction?

  • Chain transfer reaction is a termination reaction by which the free radical site of growing polymer chain is transferred to another molecule.

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Various types of Chain Transfer Reaction

  • Chain Transfer to Initiator

A polymer chain reacts with an initiator ,which terminates that polymer chain creating a new radical initiator which does not allow further propagation.

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  • Chain Transfer to Solvent
  • A hydrogen atom is abstracted from a Solvent Molecule
  • Formation of radical on the solvent molecules
  • Stops propagation further

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  • Chain Transfer to Monomer
  • A hydrogen atom is abstracted from a MONOMER
  • Resonance stabilization of this radical discourages further propagation

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  • Chain Transfer to Polymer
  • This reaction moves a carbon radical from one place to another by an intermolecular or intermolecular hydrogen atom transfer.

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Chain Transfer Agents

The compound with which the chain transfer

reaction takes place. Example : Mercaptans,CCl4,

CBr4, H2 gas etc.

  • Chain transfer to Chain transfer agents

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Retarder and Inhibitors

Retarder : The materials which slow down the

chain growth polymerization

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Inhibitors : The inhibitors stop or low down

by reacting with initiators or growing chain radicals

Example : Quinones, Phenols with bulky groups, Oxygen

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Effect of Inhibitors and Retarders

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Kinetics of Free Radical Polymerization

  • To initiate there must be free radicals

generated by the hemolytic decomposition of an

Initiator.

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  • The relation between the rate of

decomposition and the concentration of the

initiator.

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Initiator Efficiency

  • The efficiency factor ‘f’ is used to describe the effective radical concentration.
  • Due to side reactions, chain initiation is not 100%.
  • Typical values range from 0.6 to 1.0.

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  • From Arrhenius equation , the mole constant is related to Temperature ,

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  • Initiation is followed by Propagation which can be represented as :

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And the equation,

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  • The final step in polymerization is termination

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  • The corresponding equation,

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  • When the steady state prevails

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Finally, we get on substituting value,

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Equation for Kinetic Chain Length

Kinetic chain length (v) is the average number of

monomer units consumed for each radical

initiator that starts the polymerization .

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Substituting values,

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Thermodynamics of Free Radical Polymerization

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  • As temperature increases the reaction becomes less favorable
  • At Ceiling Temperature the polymerization reaches equilibrium

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Representative Enthalpies and Entropies of polymerization temp

Monomer

Enthalpies (Kj/mol)

Entropies (J/mol)

Acrylonitrile

77

109

1,3-Butadiene

78

89

Ethylene

109

155

Styrene

70

104

Propylene

84

116

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Ceiling Temperature

  • Ceiling temperature is a measure of the tendency of a polymer to revert to its constituent monomers. When a polymer is at its ceiling temperature, the rate of polymerization and depolymerization of the polymer are equal.

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Chain End Model

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  • Unsaturated linkages are most effective in stabilizing
  • Order of radical reactivity is the opposite of their order in enhancing monomer reactivity

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Ring Opening polymerization

Another form of chain-growth polymerization in

which the terminal end group of a polymer

chain acts as a reactive center where further

cyclic monomers can be added by ring-opening

and addition of the broken bond

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Ring Opening Polymerization

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Cationic ROP Anionic ROP

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Anionic Ring-opening Polymerization

  • Triggered by nucleophilic attack of the initiator to the carbon.
  • Due to ring distortion monomers with three

member ring structure undergoes Anionic ring-

opening polymerization

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Cationic Ring-opening Polymerization

  • The chain grows by the addition of cyclic

monomers thereby opening ring system

  • Has cationic initiator and intermediate

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Ionic Polymerization

“Ionic polymerization is a chain-growth

polymerization in which active centers are ions

or ion pairs”

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Ionic polymerization are two types :

  • Anionic Polymerization
  • Cationic Polymerization

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Anionic Polymerization

Anionic addition polymerization is a form of

chain-growth polymerization or addition

polymerization that involves the polymerization

of vinyl monomers with strong electronegative

groups.

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Initiation

  • The process begins with the formation of

initiator

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  • Initiator attacks the first monomer

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Propagation

  • Here the chain grows longer in the process

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Termination

  • It is the last step where H2O ,NH3 or kind of

Alcohol is used to stop the repetition

permanently

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Cationic Polymerization

The polymerization in where the initiation is

done by a ‘Proton’ and the propagation is

carried away by a ‘Carbonium ion’ is called

cationic polymerization

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Initiation

  • It can be initiated by protonic acids or Lewis

acids. Example : Sulfuric acid, Perchloric acid

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  • The initiator attacks the first monomer

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Propagation

  • Adding up of monomer units and

simultaneously transfer of the charge takes place.

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Termination

Donation of proton pairs

Donation of a proton to the counter-ion resulting

in the formation of a double bond at he end of

the growing chain,

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Termination by coupling

Formation of a covalent bond between the

carbonium-ion and the counter-ion.

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Thank You