Methods of Free Radical Polymerization

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Methods of Free Radical Polymerization

• There are four commonly used methods for free
  radical polymerization
• 1. Bulk polymerization
• 2. Solution polymerization
• 3. Suspension polymerization
• 4. Emulsion polymerization

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BULK POLYMERIZATION

• The simplest method of polymerization where the
  reaction mixture contains only the monomer and a
  monomer soluble initiator.
• Example
• PMMA

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ADVANTAGE

• Advantage of the high concentration of monomer
  result in
• 1. High rates of polymerization
• 2. High degree of polymerization
• 3. High purity of product
• 4. High molar mass polymer are produce

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DISADVANTAGE

• Increase in the reaction viscosity with
  conversion.
• difficulty in removing heat.
• autoacceleration
• if the polymer formed is insoluble in the
  monomer (such as acrylonitrile, vinyl chloride)
  gt precipitating of the polymer and we can not
  apply the kinetics.

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SOLUTION POLYMERIZATION

• This method is used to solve the problems
  associated with the bulk polymerization because
  the solvent is employed to lower the viscosity of
  the reaction, thus help in the heat transfer and
  reduce autoacceleration.
• BUT 
• The disadvantage of solvent presence is
• 1. Reduce monomer concentration which results in
  decreasing the rate of the reaction and the
  degree of polymerization.
• 2. Solvent may cause chain transfer.
• 3. Clean up the product with a non solvent or
  evaporation of solvent.

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SUSPENSION POLYMERIZATION

• This method is used also to solve the problem of
  heat transfer.
• It is similar to bulk polymerization where the
  reaction mixture is suspended as droplets in an
  inert medium.
• Monomer, initiator and polymer must be insoluble
  in the suspension media such as water.

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EMULSION POLYMERIZATION

• This is similar to suspension polymerization
  except that the initiation is soluble in
  suspension media and insoluble in the monomer.
• The reaction product is colloidally stable
  dispersion known as latex.
• The polymer particles have diameter in the range
  of (0.05 - 1 ? m) smaller than suspension.

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IONIC POLYMERIZATION

• Chain polymerization of olefinic monomers which
  can occur with charged radicals. For example
  styrene.

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• This polymerization are more monomer specific
  than free radical polymerization and will proceed
  only with monomers that have substituent groups
  which can stabilize the active center.
• For cationic polymerization the active center
  will proceed if X group is able to donate
  electrons or delocalize the positive charge.
• For anionic polymerization the active center will
  proceed if X group is able to withdraw electrons
  or delocalize the negative charge.

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Thank You

• See You Next Lecture