Polymers are macromolecules contain a
variety of functional groups. They can be joined/tailored. The word polymer,
derived from Greek words
poly - many and meres - parts. A long chain molecule composed of large number of repeating units of
identical structure.
For Example, "A" is a monomer (single unit), where A-A-A...A (n number of A's) is a
polymer.
Classification of Polymers
Polymers are classified based on their,
Source
Type of polymerization
Bio-stability
Structure
Based on the source
1. Natural Polymers
Occur naturally. Found in plants and animals.
Proteins, enzymes, muscle fiber, polysaccharide are the natural polymers
that are used in the pharmaceutical formulation.
Example, Chitosan, Carrageenan, Isapghula, Acacia, Agar, Shellac and
Dextran
2. Semi-Synthetic Polymers
Obtained from naturally occurring polymers and treated with
chemical.
Example, Hydroxypropyl methylcellulose (HPMC), Methylcellulose (MC),
Hydroxypropyl Cellulose (HPC)
3. Synthetic Polymers
They are industrially produced. Several molecules are
linked together with a covalent bond.
Example, Polystyrene, Polyester, Polyethylene, Polyamides and
Polyglycolic Acid.
Based on the type of Polymerization
1. Addition Polymerization
Formed from the
simple addition of monomer molecules to each other by a chain mechanism. It is a quick one.
Example, Polyethylene and Polypropylene
2. Condensation Polymerization
Formed from
intermolecular reactions between
bifunctional or polyfunctional monomers having reactive functional
groups such as -OH, -COOH etc.
Example, Polyurethane and Polyester
Based on Bio-Stability
1. Biodegradable Polymers -
Degraded by micro-organisms (bacteria and fungi) within a suitable period of
time. Example, Polylactic acid and Polyglycolic acid.
2. Non-Biodegradable Polymers -
These are made up of long carbon chains with strong chemical bonds. Hence are
harder to be broken down by microbes. Example, Ethyl cellulose, Polydimethyl
siloxane.
Based on Structure
1. Linear polymers
Similar in
structure to a long straight chain compound. These polymers have high melting
points and higher density.
Example, PVC (Poly-Vinyl Chloride)
2. Branched chain polymers
In these polymers, branches originates at random points
from a single linear chain. Because of these branches, the polymers are
not closely packed together. They are of low density having low melting
points.
Example, Low Density Poly Ethylene (LDPE)
3. Cross-linked or Network Polymers
Monomers are linked together to form a three dimensional
network. These are brittle and hard. Example, Bakelite and Melamine.
