Polymerization

What is polymerization?

A process of making the monomer molecules react together in a chemical reaction and produce three-dimensional networks or polymer chains is called polymerization.

Degree of polymerization

The main characteristic of polymer which determines the physical properties of polymer materials is defined as the degree of polymerization. A large molecule made up of rings or chains of linked repeating subunits referred to as monomers is called polymer. They generally have high boiling and melting points.

How to calculate the degree of polymerization?

Step 1: Write the chemical formula of the polymer.

Example, let us consider tetrafluoroethylene. Its chemical formula is written as -(CF2-CF2)n -. The monomer unit is put in the parentheses.

Step 2: Determine the atomic mass.

Determine the atomic mass of the elements composed in the monomer unit with the help of periodic table. In the case of tetrafluoroethylene, the atomic mass of carbon is 12 and the atomic mass of fluorine is 19.

Step 3: Evaluate the molecular weight.

To calculate the molecular weight follow the sequence below:

  • Multiply the atomic mass of carbon element by the number of carbon atoms in the monomer
  • Multiply the atomic mass of fluorine element by the number of fluorine atoms in the monomer
  • Add the products
  • Therefore, the molecular weight of tetrafluoroethylene is 12 x 2 + 19 x 4 = 100.

Step 4: Divide.

Divide the molecular mass of the polymer by the molecular weight of the monomer. For example, if the molecular mass of tetrafluoroethylene is 1,20,000, then its degree of polymerization is calculated as 1,20,000 / 100 = 1,200.

Therefore, the degree of polymerization is 1,200.

Types of polymerization

Based on the mode of polymerization of polymers, there are two types of polymerization. They are addition polymerization and condensation polymerization.

Condensation polymerization

The formation of condensation polymers occurs by the repeated condensation reaction between two different tri-functional or bi-functional monomeric units. In this type of reaction, small molecules such as alcohol, water, hydrogen chloride, etc. are eliminated. Some examples are nylon 6, nylon 6, 6, terylene (dacron), etc. Formation of nylon 6, 6 occurs due to the condensation of (C6H16N2) hexamethylene diamine with (C6H10O4) adipic acid.

Addition polymerization

The formation of addition polymers occurs by the repeated addition of monomer molecules which possess triple or double bonds. For example, the formation of ((C3H6)n) polypropene from (C3H6) propene, and ((C2H4)n) polythene from (C2H4) ethene.

  • Homopolymers – The formation of addition polymers due to the polymerization of single polymeric species is called homopolymer. For example, polythene (C2H4)n).
  • Copolymers – The formation of addition polymers which occur due to by addition polymerisation from two different monomers is called copolymer. For example, Buna-N, Buna-S, etc.

Polymerization techniques

  1. Addition polymerization:
    • Bulk polymerization
    • Solution polymerization
    • Suspension polymerization
    • Emulsion polymerization
  2. Condensation polymerization:
    • Melt polycondensation
    • Solution polycondensation

Frequently Asked Questions on polymerization

How polymers are formed?

Many molecules of a simple compound combine together to form a polymer.

How to prevent polymerization?

Polymerization can be prevented by adding polymerization inhibitors.

What is depolymerization?

The process of converting a polymer into a mixture of monomers or a monomer through increased entropy is called depolymerization.

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