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Polymerization Reactions


The chemical reaction in which high molecular mass are formed from monomers is known as POLYMERIZATION.

The processes of polymerization are divided into two groups:

  • Condensation or Step-Reaction Polymerization
  • Addition or Chain-Reaction Polymerization
  • Condensation or Step-Reaction Polymerization:

    Condensation takes place between two polyfunctional molecules to produce one larger polyfunctional molecule, with the possible elimination of a small molecule such as water. The reaction continues until almost all of one of the reagents is used up; an equilibrium is established which can be shifted at will at high tempreatures by controlling the amounts of the reactants and products.

    Nylon 66 is an example of a common polymeric clothing material, invovling one each of two monomers, hexamethlene diamine and adipic acid, reacting to form a dimer of Nylon 66.

    [nylon 66]

    There are two types of condensation polymers:

  • Polymaid (Nylon)
  • Polyester

    Addition or Chain-Reaction Polymerization:

    Addition polymerization involves chain reaction in which the chain carrier may be an ion or a reactive substance with one unparied electron called a free radical. A free-radical is a chemical component that contains a free electron that forms a covalent bond with an electron on another molecule. The free radical can react to open the double bond of a Vinyl monomer and add to it, with one electron remaining unpaired. In a very short time, many more monomers add successively to the growing chain. Finally two free radicals react to end each other's growth activity and form one or more polymer molecules. Ethylene is an example of a monomer used to make a common polymer.

    [ethylene]

    The polymerization process of Addition or Chain-Reaction Polymerization consists of three steps:

  • Initiation
  • Propagation
  • Termination

    To view these steps click here to visit the Scientific Principles site (it's not my site), or for general information on these steps, click here to visit the Scientific American site (agin this is not mine).

    Examples of some important addition polymers:

  • Polytetrafluroethylene (Teflon)
  • Polyethylene
  • Polystyrene

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