Polymer Classification

A polymers is defined as a large molecule (or macromolecule), formed by joining together thousands of smaller molecule units by chemical bonds (or covalent bonds).

Classification of Polymers

•Based on origin or source

There are three types of polymers based on the source (or origin) and these are;

(A)Natural polymers

Natural polymers are those polymers that occur naturally in plants or animals. Example of these polymers are proteins, cellulose, starch, resins and rubbers etc.

(B)Semi-synthetic polymers

Semi-synthetic polymers are polymers that are obtained by artificially modifying natural polymers in the laboratory. Example of these polymers are cellulose acetate, cellulose nitrate, hydrogenated natural rubber, etc.

(C)Synthetic polymers

They are also known as man-made polymers. These polymers are synthesized artificially in the laboratory by humans. Example of these polymers are Polyethylene, synthetic fibres, nylon-6, Buna-s, polyesters, etc.

"Plastics are the most common and widely used synthetic polymers".

•Based on Structure

There are also three types of polymers based on their structure and these are;

(A)Linear Polymer

These polymers form when monomer units are linked together on a regular basis (or in a linear fashion). Or the structure of polymers with long and straight chains falls into this category. Example of these polymers are PVC (poly-vinyl chloride), high density polyethylene, etc.

(B)Branched Polymers

When the linear chains of a polymer form branches, such polymers are classified as branching chain polymers. Example of these polymers are low density polyethylene, amylopectin, etc.

(C)Cross-link polymers

When multiple branches are connected to each other in a single polymer and this results in the formation of a 3D structure, then this polymer is called a 3D structure polymer or a cross-linked polymer. Example of these polymers are Bakelite, melamine, etc.

•Based on the number of monomers

There are two types of polymers based on the number of monomers and these are;

(A)Homopolymer

A polymer consisting of the same type of monomer unit is called a homopolymer. Only one type of monomer molecule is present in this polymer molecule. Example of these polymers are Polyethylene, polyvinyl chloride, polypropylene, etc.

(B)Hetero-polymer/ Co-polymer

A polymer consisting of more than one type of monomer units is called hetero-polymer. More than one type of monomer molecule is present in this polymer molecule. Many commercially important polymers are copolymers. Example of these polymers are kelvar, polyesters, Bakelite, Nylon-66, etc.

•Based on the backbone chain in polymer structure

There are two types of polymers based on the backbone chain present in polymer structure and these are;

(A)Organic polymers

Most of the polymers around us are made of hydrocarbon backbones. The hydrocarbon backbone is a long chain of carbon and hydrogen atoms and these polymers are organic polymer. A few examples of a hydrocarbon backbone polymer are polypropylene, polystyrene,  proteins, cellulose, rubbers, etc.

(B)In-organic polymers

If carbon and hydrogen atoms are not present in the backbone chain of the polymer structure, the polymer is known as an inorganic polymer. Example of these polymers are glass, silicon rubber,etc.

•Based on the polymerization techniques

Based on the polymerization techniques, polymers are of two types and they are;

(A)Addition polymers

These types of polymers are formed by the repeated addition of a monomer molecule to the polymer chain. The polymerization of unsaturated hydrocarbons ( having double and triple bonds) falls in this category. No elimination of smaller molecules such as water, carbon-dioxide,etc. Example of these polymers are Polyethylene, polypropylene, polystyrene, etc.

(B)Condensation polymers

These polymers are formed by the combination of monomers with the elimination of small molecules such as water, alcohol, etc. These monomers are generally bi-functional and tri-functional. Example of these polymers are polyesters, nylons, etc.

•Based on the functionality of monomer molecules

Functionality refers to the number of active sites or groups or bonds present on the monomer unit. It is denoted by a symbol 'f'. 

         Functionality, f ＝ 2 ➝ linear Polymers

         Functionality, f ≽ 3 ➝ Cross-linked polymers

Based on the functionality of monomer molecules, polymers are of three types and they are;

(A)Monofunctional

When only a single reactive group is present on the monomer molecule, the polymer formed from such monomer molecules is called monofunctional or uni-functional polymer.

(B)Di-functional

When two reactive groups are present on a monomer molecule, the polymer formed from such monomer molecules is called a di-functional polymer. Double-bonded monomer molecules are considered as bi-functional monomers.

(C)Tri-functional

When three reactive groups are present on a monomer molecule, the polymer formed from such monomer molecules is called a tri-functional polymer. Triple-bonded monomer molecules are considered as tri-functional monomers.

•Based on the molecular forces present in monomer molecules

Intramolecular forces (or molecular forces) are the forces that holds the atoms together within a molecule. Based on the molecular forces present in the monomer molecule, polymers are of four types and they are;

(A)Elastomers

In this type of polymer, the polymer chain is held in place by the weakest intramolecular forces. Due to this, these are rubber-like solid polymers that are elastic in nature, which means the polymer can easily stretch or compress when we apply a force on it. For example- rubber bands, vulcanised rubber, etc. 

(B)Thermoplastic

In this type of polymer, the polymer chain is held in place by the "Van-der waals" intramolecular forces. These are long-chain molecules. Example of these polymers are PVC (poly-vinyl chloride), polystyrene ,etc.

(C)Thermosetting

In this type of polymer, the polymer chain is held in place by the strong covalent intramolecular forces. Due to that, their structure are strong 3D (three dimensional) network or cross-linked. Example of these polymers are Bakelite, Urea-formaldehyde resins, etc.

(D)Fibres

In this type of polymer, the polymer chain is held in place by the strong intermolecular forces such as hydrogen bonds or dipole-dipole interaction forces. Due to the strong forces, the chains are closely packed providing high tensile strength and low elasticity. Example of these polymers are Polyesters, Polyamide (such as Nylon-6, Nylon-66), Phenol-formaldehyde, silk, etc.

Silk

•Based on Tacticity

Tacticity can be defined as the geometric arrangement of a characteristic group of the monomer unit with respect to the main chain (backbone chain) of the polymer. Based on the tacticity, polymers are of three types and they are;

(A)Atactic

A polymer is called an Atactic polymer when the characteristic groups (or side groups) of a monomer chain are arranged in an irregular fashion (or randomly) around the main chain.

(B)Isotactic

A polymer is called an Isotactic polymer when the characteristic groups (or side group) of a monomer chain are arranged on the same side of the main chain.

(C)Syndiotactic

A polymer is called an Syndiotactic polymer when the characteristic groups (or side group) of a monomer chain are arranged in an alternative manner around the main chain.

•Based on degradability

Two types of Polymers are there based on the degradation and they are;

(A)Biodegradable Polymers

Those polymers which are degraded and decayed by acids, microorganisms (such as bacteria) present in the environment, are known as biodegradable polymers. These types of polymers are used in surgical bandages, capsule coatings and in surgery. All types of condensate polymers are biodegradable such as Poly-hydroxy-butyrate, Nylons, Polyesters,etc.

(B)Non-biodegradable Polymers

The Polymers that cannot be destroyed or decayed in the environments by itself, are called Non-biodegradable polymers. The best example of this type of polymers are "Plastics".

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