6. Chain growth
polymerization
• Addition polymerization
• All the atoms in monomer is used to produce a polymer.
• Steps in chain reaction:
• initiation
• propagation
• termination
7. Step growth
polymerization
Polymerization mechanism in which bi-functional or
multifunctional monomers react to form first dimers,
then trimers, longer oligomers and eventually long
chain polymers.
•Eg: polyesters, polyamides, polyurethanes. Etc
•Polymer+molecule with low molecular weight.
8. Differences between step-growth polymerization and
chain-growth polymerization
Step growth Chain growth
• Growth throughout matrix • Growth by addition of monomer
only at one end of chain
• Rapid loss of monomer early
in the reaction • Some monomer remains even at
long reaction times
• Similar steps repeated
• Different steps operate at
throughout reaction process
different stages of mechanism.
• Average molecular weight
• Molar mass of backbone chain
increases slowly at low increases rapidly at early stage
conversion and high extents and remains approximately the
of reaction are required to same throughout the
obtain high chain length. polymerization
• Ends remain active (no • Chains not active after
termination) termination
• No initiator necessary • Initiator required
9. Free radical
polymerization
• Initiation: active center created.
• 2 steps
• Radicals from initiators
• Transfer to monomer
• Types of initiation:
• Thermal decomposition
• Photolysis
• Redox reactions
• Persulfate
10. • Propagation:
• Termination :
• Combination of two active chain ends
• Impurities
• Combination of an active chain end with an initiator radical
11. Cationic polymerization
• Cationic initiator binds & transfers charge to monomer.
• Reactive monomer reacts with other monomer to form a
polymer.
• Active site: carboniumion ,
oxonium, sulfonium or phosphonium ion
• Monomers: alkoxy. phenyl, vinyl, 1,1-dialkyl-substituted
alkene monomers.
• Initiator: provide electrophile
eg: bronsted acids(acetic acid,HCL), Lewis acids+electron
donor.
• Application :polyisobutylene.
13. Anionic polymerization
• Carried out through carbanion active species.
• Monomer: vinyl monomers with substituents on double bond
able to stabilise a –ve charge.
o Eg: styrene, dienes, methacrylate,
vinyl pyridine, aldehydes, epoxide, episulfide
cyclic siloxane, and lactones
• Polar monomers:
o eg: acrylonitrile, cyanoacrylate, propylene oxide,
vinyl ketone, acrolein, vinyl sulfone,
vinyl sulfoxide, vinylsilane andisocyanate.
• .
15. Insertion polymerization
• Coordination polymerization
• Monomer adds to growing macromolecule through an
organometallic active center.
• Ziegler natta catalysts- titanium tetrachloride+aluminium
cocatalyst.
• Mechanism;
16. Ring opening polymerization
• Initiation: Ring cleavage
• Propagation:Attachment of cyclic monomers.
• Termination
• examples
o PA 6: Polycaprolactame from caprolactam
o PCL : Polycaprolactone from caprolactone
o Polyethylene oxide from ethylene oxide
o Polypropylene oxide from propylene oxide
18. Bulk polymerization
• Mass or block polymerization: Polymerization of the undiluted
monomer.
• carried out by adding a soluble initiator to pure monomer into
liquid state.
• Viscosity increases dramatically during conversion
• 2 types
o Quiescent bulk polymerization
o Eg: phenol- formaldehyde condensation
o Stirred bulk polymerization
o Eg: nylon 66.
19.
20.
21. Advantages Disadvantages
• The system is simple and • Heat transfer and mixing
requires thermal insulation. become difficult as the
• The polymer is obtained pure. viscosity of reaction mass
increases.
• Large castings may be
• Highly exothermic.
prepared directly molecular
weight distribution can be • The polymerization is
easily changed with the use obtained with a
of a chain transfer agent. broad molecular weight
distribution due to the
high viscosity and lack of
good heat transfer.
• Very low molecular weights
are obtained.
22. Solution polymerization
Monomer dissolved in solvent, formed polymer stays dissolved.
Depending on concentration of monomer the solution does not
increase in viscosity.
Advantages Disadvantages
* Product sometimes * Contamination
directly usable with solvent
* Controlled heat * Chain transfer to
release solvent
* Recycling solvent
Applications
Acrylic coating, fibrespinning, film casting
27. Advantages Disadvantages
• Surfactants and
• High molecular
polymerization adjuvants -
weight polymers
difficult to remove
• fast polymerization rates.
• For dry (isolated) polymers,
• allows removal of heat from water removal is an energy-
the system. intensive process
• viscosity remains close to • Designed to operate at high
that of water and is not conversion of monomer to
dependent on molecular polymer. This can result in
weight. significant chain transfer to
• The final product can be used polymer.
as such ,does not need to be • Can not be used for
altered or processed condensation, ionic or
Ziegler-Natta polymerization.
