Addition polymerization

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Characteristics

• polymerization process takes place in three distinct steps:

1. chain initiation
   Initiation (chemistry)
   
   In chemistry, initiation is a chemical reaction that triggers one or more secondary reactions. Often the initiation reaction generates a reactive intermediate from a stable molecule which is then involved in secondary reactions....
   , usually by means of an initiator
   Initiator
   
   An initiator can refer to:* Pyrotechnic initiator, a device containing a pyrotechnic composition used primarily to ignite other, more difficult to ignite materials...
    which starts the chemical process. Typical initiators include any organic compound with a labile group: e.g. azo (-N=N-), disulfide (-S-S-), or peroxide (-O-O-). Two examples are benzoyl peroxide
   Benzoyl peroxide
   
   Benzoyl peroxide is a chemical in the organic peroxide family. It consists of two benzoyl groups joined by a peroxide group. Acceptable condensed structural formulae would include C6H5-COO-OOC-C6H5, PhCO-O-O-COPh, and 2O2....
    and AIBN.
2. chain propagation
   Chain propagation
   
   Chain propagation is a process in which a reactive intermediate is continuously regenerated during the course of a chemical reaction. In polymerization reaction, the reactive end-groups of a polymer chain react in each propagation step with a new monomer molecule transferring the reactive group to that last unit....
   
3. chain termination
   Chain termination
   
   Chain termination is any chemical reaction leading to the destruction of a reactive intermediate in a chain propagation step in the course of a polymerization, effectively bringing it to a halt....
   , which occurs either by combination or disproportionation
   Disproportionation
   
   Disproportionation or dismutation is used to describe two particular types of chemical reaction:* A chemical reaction of the type: 2A ? A' + A" where A, A' and A" are different chemical species....
   . Termination, in radical polymerization, is when the free radicals combine and is the end of the polymerization process.

• some side reactions may occur, such as: chain transfer to monomer, chain transfer to solvent, and chain transfer to polymer.

• unlike condensation polymerization (also known as step-growth polymerization
  Step-growth polymerization
  
  Step-growth polymerization is a polymerization process that involves a chemical reaction between multifunctional monomer molecules. In a step-growth reaction, the growing chains may react with each other to form even longer chains....
  ):
• high molecular weight polymer is formed at low conversion
• no small molecules, such as H₂O
  Water
  
  Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
  , are eliminated in this process
• new monomer adds on the growing polymer chain via the reactive active centre which can be a
• free radical in free radical addition polymerisation
• carbocation
  Carbocation
  
  A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer Electron shell#Valence shell instead of the eight valence electrons that ensures maximum stability ....
   in cationic addition polymerisation
• carbanion
  Carbanion
  
  A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons ....
    in organometallic complex in coordination polymerisation
  Coordination polymerization
  
  Coordination polymerization is a form of addition polymerization in which monomer adds to a growing macromolecule through an organometallic active center....
  
• the monomer molecule can be a
• unsaturated compound
  Unsaturated compound
  
  In organic chemistry, an unsaturated compound is a chemical compound that contains carbon-carbon double bonds or triple bonds such as in alkenes or alkynes....
   like ethylene
  Ethylene
  
  Ethylene is the chemical compound with the formula C2H4. It is the simplest alkene. Because it contains a carbon-carbon double bond, ethylene is called an unsaturated hydrocarbon or an olefin....
   or acetylene
  Acetylene
  
  Acetylene is the chemical compound with the symbol carbonhydrogen. It is the simplest alkyne.As an alkyne, acetylene is Saturation because its two carbon atoms are Chemical bond together in a triple bond....
   which make them reactive, see vinyl polymer
  Vinyl polymer
  
  Vinyl polymers are a group of polymers derived from vinyl monomers. Their backbone is an extended alkane chain, made by polymerizing an alkene group into a chain ....
  
• Alicyclic compound
  Alicyclic compound
  
  An alicyclic compound is an organic compound that is both aliphatic and cyclic compound. They contain one or more all-carbon rings which may be either saturation or unsaturated, but do not have aromaticity character....
  , see ring-opening polymerisation
  Ring-opening polymerization
  
  In polymer chemistry, ring-opening polymerization is a form of addition polymerization, in which the terminal end of a polymer acts as a reactive center, where further cyclic compound join to form a larger polymer chain through ionic propagation....
  
• given special reactants and reaction conditions an addition polymerization can be considered a living polymerization
  Living polymerization
  
  In polymer chemistry, living polymerization is a form of addition polymerization where the ability of a growing polymer chain to chain termination has been removed ....
  .
• above a certain ceiling temperature, no polymerisation occurs.

Examples

• benzoyl peroxide
  Benzoyl peroxide
  
  Benzoyl peroxide is a chemical in the organic peroxide family. It consists of two benzoyl groups joined by a peroxide group. Acceptable condensed structural formulae would include C6H5-COO-OOC-C6H5, PhCO-O-O-COPh, and 2O2....
   is a radical initiator
  Radical initiator
  
  In chemistry, radical initiators are substances that can produce radical under mild conditions and promote radical polymerization reactions. These substances generally possess weak bonds—bonds that have small bond dissociation energy....
   for the free radical addition polymerisation of styrene
  Styrene
  
  Styrene, also known as vinyl benzene as well as many other names , is an organic compound with the chemical formula C6H5CH=CH2....
   to produce polystyrene
  Polystyrene
  
  Polystyrene , sometimes abbreviated PS, is an Aromaticity polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry....
  .
• Aluminium chloride
  Aluminium chloride
  
  Aluminium chloride is a chemical compound of aluminium and chlorine. The solid has a low melting and boiling point, and is Covalent bond. It sublimation at 178 ?Celsius....
   is an initiator for the cationic addition polymerisation of isobutylene
  Isobutylene
  
  Isobutylene is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene , one of the four isomers of butylene. At standard temperature and pressure it is a colorless flammable gas....
   to form isobutyl synthetic rubber
  Synthetic rubber
  
  Synthetic rubber is any type of artificially made polymer material, which acts as an elastomer. An elastomer is a material with the mechanical property that it can undergo much more Elasticity deformation under stress, than most materials and still return to its previous size without permanent deformation....
  .