PE335: Polymerization Techniques

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PE335Polymerization Techniques
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Production Steps
Monomer
Co-monomer(s)

• Type of polymerization

Co-catalysts Donors etc.
Initiator/Catalyst
Technique/Reactor
Reaction conditions
Compounding/Processing
Polymer resin
End Product
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Polymerization Techniques

• 1. Homogeneous systems
• 1.1. Bulk polymerization
• 1.2. Solution polymerization
• 2. Heterogeneous systems
• 2.1. Suspension polymerization
• 2.2. Emulsion polymerization
• 2.3. Precipitation polymerization
• 2.4. Polymerization in solid state
• 2.5. Polymerization in the gas phase

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Advantages and Limitations
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Choice of Polymerization Technique
Sometimes for one monomer several techniques of
polymerizing are available. Choice of a specific
technique depends on certain factors

• Kinetic / mechanistic factors related to chain
  length, chain composition
• Technological factors e.g. heat removal, reaction
  rate, viscosity of the reaction mixture,
  morphology of the product
• Economic factors production costs, environmental
  aspects, purification steps etc.

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Bulk Polymerization

• Neat monomer (and initiator)
• Simplest formulation and equipment
• Most difficult in control, when polymerization
  is very exothermic
• Common problems (1) heat transfer (2) increase
  in viscosity
• If polymer is insoluble in monomer ? polymer
  precipitate
• (1) viscosity would remain similar
• (2) occlusion of radicals (within the polymer
  droplet) is unavoidable
• Radical occlusion ? autoacceleration ?
  crosslinked polymer nodules
• (i.e. popcorn polymerization)
• The crosslinked nodules (light weight and large
  volume) may cause
• fouling or fracture of the polymerization
  apparatus

Commercial uses

• Casting formulations
• Low MW polymers for adhesives, plasticizers,
  tackifiers,
• and lubricant additives

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Suspension polymerization

• Disperse monomer droplets in a noncompatible
  liquid (e.g. H2O)
• Polymerize the monomer by an initiator (soluble
  in the monomer)
• Stabilize the dispersion with a stabilizer (e.g.
  poly(vinyl alcohol) or methyl cellulose)
• Isolate granular bead products by filtration or
  spray drying
• Heat transfer is efficient and reaction is
  easily controlled
• Similar to bulk polymerization in kinetics and
  mechanism

Commercial uses
For making granular polymers, e.g. PS, PVC, PMMA
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Solution Polymerization

• Use monomer solution
• Heat transfer is very efficient
• MW may be severely limited by chain transfer
  reaction
• (probably caused by the solvent molecule or
  its impurities)
• Solvent residues ? difficult to remove
  completely
• Environmental concerns ? organic solvent waste

Use supercritical CO2 as a polymerization solvent
? nontoxic, inexpensive,
easily removed and recycled
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Solution Polymerization
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Emulsion polymerization

• Emulsification
• Add emulsifying agent (e.g., soap or detergent)
  in an aqueous solution
• ? to form micelles
• Monomers enter and swell the micelles
• Initiation
• Radicals (redox type) are generated in the
  aqueous phase and diffuse
• into micelles
• Propagation
• Polymerization propagated within micelles
• More monomers enter micelles to support the
  polymerization
• Termination
• Termination by radical combination when a new
  radical enters the
• micelle
• Results
• Extremely high MW are obtainable, but often too
  high to be useful
• Chain transfer reagents are often added to
  control the MW
• Also suitable for tacky polymers (? small
  particles are relative stable and
• can resist agglomeration)

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Stages of Particle Growth

• Three different stages
• Nucleation of particles
• Particle growth in presence of
• monomer droplets
• (3) Particle growth in absence of
• monomer droplets

(Thoenes, 1991)
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Emulsion Polymerization Recipe

• Water (continuous phase)
• Water-insoluble monomer
• Water-soluble initiator
• Surfactant

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Emulsion Polymerization Recipe
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Gas Phase Polymerization Light olefins

• Fluidized bed polymerization

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Hybrid Reactor for Polypropylene

• The process is a mass polymerization of
  propylene
• A catalytic system is prepared and made to react
  in a controlled manner with a small amount of
  liquid propylene, inside a small- capacity
  reactor (prepolymer)
• 2) The product of the pre-polymer is taken to the
  Loop tubular reactors (pressure of 32 bars and
  70C) for further polymerization .

3) Separation of the non-reacted monomer from the
solid polymer by gasification of the (un-reacted)
liquid propylene. 4) The polypropylene is washed
with water vapor to eliminate any still- active
catalyst, then dried with hot nitrogen. 5) PP is
compounded according to the requirements of its
specific application.
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End