Addition Polymer

Addition Polymer (chain growth polymer) - polymer made by the addition on one monomer to another without the loss of atoms

Addition polymers are formed by monomers just "adding on" to each other without the loss of atoms.  All monomers forming addition polymers, have C=C bonds (carbon-carbon double bonds).  These double bonds open up as the monomers join in chains 1000 to 10,000 units long.  For example, ethylene molecules can join together (under the proper conditions of temperature, pressure, and catalyst) to form polyethylene:

                             -(CH₂=CH₂)-_n

Usually an initiator is used to start this polymerization reaction.  The initiator is a compound that can form a free radical (a substance that contains an unpaired electron).  When free radicals react with a double bond, a chain reaction occurs, which could theoretically continue as long as there is monomer material present.  In the equation below, RO^. is a generalized symbol for a free radical initiator.

                                                                            CH₂=CH₂

CH₂=CH₂  +  RO^.                RO - CH₂ - CH₂^.                 RO - CH₂   CH₂ - CH₂^.

Other addition polymers include polymethyl methacrylate (Lucite^TM or Plexiglass^TM), TeflonTM, polyvinyl alcohol, polystyrene, polyvinyl chloride (PVC), polyacrylonitrile (Orlon^TM), and natural rubber.

Addition Polymers