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Addition Polymerization

  • Polymers which are formed by addition reaction are known as addition polymers.
  • If monomer is ethylene or its derivative, then addition polymer is either linear polymer or branched-chain polymer. Examples are polystyrene, polytetrafluoroethylene, and polyacrylonitrile.
  • If monomer is 1,3-butadiene or 2-substituted-1,3-butadiene Description: 49416.png, then polymer is always branched-chain polymer.
    Description: 49424.png
    G Monomer Polymer
    H 1,3-Butadiene Polybutadiene
    CH3 2-Methyl-1,3-butadiene Polyisoprene
    Cl 2-Chloro-1,3-butadiene or chloroprene Polychloroprene (neoprene)
  • Addition polymers retain all the atoms of the monomer units in the polymer.
  • Addition polymerization takes place in three steps: initiation, chain propagation, and chain termination.
  • Addition polymers are called as chain growth polymers.

Types of addition polymerization

Radical polymerization: This type of polymerization is performed by heating the monomer with only a very small amount of the initiator or by exposing the monomer to light. The general mode of radical polymerization of vinyl monomers is depicted as follows:

Chain initiation step
Initiator In Description: 49432.png

Chain propagating step
Description: 49442.png

Chain terminating step
Description: 49451.png
In case the alkene is a diene, the following kinds of polymerization are possible:
  • 1,4-Polymerization: When the polymerization takes place at C1 and C4 of butadiene, an unbranched polymer is formed. This product is different from that formed from an alkene having a double bond, which at each of its carbons is substituted by different groups and hence can exist either as trans-polybutadiene or cis-polybutadiene or a mixture as shown:
    Description: 49843.png
  • 1,2-Polymerization: Alternatively, 1,3-butadiene can undergo polymerization at C1 and C2 to yield the polymeric product, polyvinyl polythene.
    Description: 49461.png
  • Cationic polymerization: Polymerization which is initiated by an electrophile is known as cationic polymerization. Electrophile commonly used for initiation is BF3 OEt2.
  • Anionic polymerization: Anionic polymerization takes place in the presence of nucleophile, which is initiator in this polymerization.
    The suitable initiator can be NaNH2 or RLi.
    Description: 49470.pngDescription: 49478.png
    Description: 49486.pngDescription: 49494.png

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