Polymer Techniques/ Polymerization Process

The word polymer is a combination of two Greek words- 

              Poly means 'many'  

          Or Mers means 'parts of unit

    ☆ Poly + Mers ➝ many parts of unit

In polymer chemistry; 

Polymerization is a process in which thousands of smaller molecules called "monomers" join together to form larger molecules called "macromolecules/polymers". They have high molecular weight.

Or

"It can also be defined as the fundamental process by which low molecular weight compounds are converted into high molecular weight compounds".

      

Polymerization Processes

Several different categories of polymerization reactions exist, but the most notable of which are: step-growth polymerization and chain growth polymerization. 

(a) Chain growth polymerization / Addition polymerization

"Chain-growth polymerization reaction" also known as "Addition polymerization reaction". In this polymerization reactions, monomer molecules bond to each other to form a larger molecule called a polymer, without removing any of the smaller molecules as a byproduct.                    Since only one type of monomer is used to form larger molecules in this polymerization technique, the resulting polymer is a homopolymer with a linear or branched structure. In this, unsaturated monomers are generally used. 

Addition polymerization usually occurs in the presence of a catalyst. Examples of polymers formed by addition polymerization Polyvinyl chloride (PVC), Polystyrene, Acrylic, Polypropylene, high and low density Polyethylene, Teflon, etc.

          

The addition of a new monomer unit takes place by chain reaction once at a time. During this, all monomers are consumed and no byproducts are formed. 

Addition polymerization occurs in four ways-

• Free Radical Polymerization
• Cationic Chain Polymerization
• Anionic Chain Polymerization
• Co-ordination Polymerization

(B)Condensation polymerization or step growth polymerization

"Step-growth polymerization reaction" also known as "Condensation Polymerization reaction". In condensation polymerization, polymer molecules are formed by independent reactions between functional groups of a simple monomer units. 

In this, each step involves the combination of two polymers (or generally two different or same oligomers) of different or equal chain lengths to form a longer molecule. The reaction is a long process and the molecular mass increases very slowly.

             

In this, polymer formation occurs when some of the smaller molecules are lost as a byproduct through a reaction where the monomer molecules are joined together. Usually, water molecules is released as a by-product. Monofunctional, Bi-functional and Tri-functional monomers are commonly used in this polymerization technique. 

Examples of polymers formed by condensation polymerization are Cellulose, Starch, Polyesters, Polyamide, Proteins, Carbohydrates, etc. 

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