Classification of Polymers

There are several ways of classification of polymers based on some special considerations. The following are some of the common classifications of polymers:

Classification based on source

Natural polymers

Ø Natural polymers are polymers which occur in nature 

Ø These polymers are found in plants and animals.

Ø Examples are proteins, cellulose, starch, some resins and rubber.

Semi-synthetic polymers

Ø Semi-Synthetic polymers are polymers obtained by making modification in natural polymers artificially in a lab.

Ø These polymers formed by chemical reaction (in a controlled environment) and are of commercial importance.  

Ø Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the usual examples of this sub category.

Synthetic polymers

Ø Synthetic polymers are polymers which humans can artificially create/synthesize in a lab. 

Ø These are commercially produced by industries for human necessities.

Ø Examples of manmade polymers extensively used in daily life as well as in industry are plastic (polythene), synthetic fibres (Nylon- 6, 6) and synthetic rubbers (Buna - S).

Classification based on structure of polymers

Linear Polymers

Ø These polymers consist of long and straight chains.

Ø The examples are high density polythene, polyvinyl chloride, etc.

Ø These chains do not have any side chain.

Ø These are represented as:

Branched chain Polymers

Ø These polymers contain linear chains having some branches.

Ø For example, low density polythene.

Ø These are depicted as follows:

Cross-linked or Network polymers

Ø These are usually formed from bi-functional and tri-functional monomers.

Ø They contain strong covalent bonds between various linear polymer chains, e.g. Bakelite, melamine, etc.

Ø These polymers are depicted as follows:

Addition polymers

Ø The addition polymers are formed by the repeated addition of monomer molecules possessing double or triple bonds, e.g., the formation of polythene from ethene and polypropene from propene. However, the addition polymers formed by the polymerisation of a single monomeric species are known as homopolymers, e.g., polythene.

Ø The polymers made by addition polymerisation from two different monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc.

Condensation polymers

Ø The condensation polymers are formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units.

Ø In these polymerisation reactions, the elimination of small molecules such as water, alcohol, hydrogen chloride, etc. take place.

Ø The examples are terylene (dacron), nylon 6, 6, nylon 6, etc. For example, nylon 6, 6 is formed by the condensation of hexamethylene diamine with adipic acid.

Classification based on molecular forces

Elastomers

Ø These are rubber – like solids with elastic properties.

Ø In these elastomeric polymers, the polymer chains are held together by the weakest intermolecular forces.

Ø These weak binding forces permit the polymer to be stretched.

Ø A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber.

Ø The examples are buna-S, buna-N, neoprene, etc.

Fibres

Ø Fibres are the thread forming solids which possess high tensile strength and high modulus.

Ø These characteristics can be attributed to the strong intermolecular forces like hydrogen bonding.

Ø These strong forces also lead to close packing of chains and thus impart crystalline nature.

Ø The examples are polyamides (nylon 6, 6), polyesters (terylene), etc.

Thermoplastic polymers

Ø These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling.

Ø These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres.

Ø Some common thermoplastics are polythene, polystyrene, polyvinyls, etc.

Thermosetting polymers

Ø These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible.

Ø These cannot be reused.

Ø Some common examples are bakelite, urea-formaldelyde resins, etc.

Classification based on growth polymerisation

The addition and condensation polymers are nowadays also referred as chain growth polymers and step growth polymers depending on the type of polymerisation mechanism they undergo during their formation.

Po Polymer	La large molecules having high molecular mass formed by combination of number of small units called monomers.
P Polymerisation	Th The process of formation of polymers from respective monomers.
Na Natural polymers	Fofound in plants and animals. Examples:  proteins, cellulose, starch.
Sy Synthetic polymers:	Sy synthesized in laboratory from natural material. Example,  nylon 6, 6 , Buna-S
Addition Polymers	Formed by repeated addition of monomers having multiple bonds .
H Homopolymers.	Aa Addition polymers formed from single monomeric species
Copolymers	A Addition polymers formed from two different monomeric species
C Condensation polymers	F Formed by repeated condensation of different bi or tri-functional monomer units.
F Fibers	L Long thin, threadlike bits of material that are characterized by great tensile (pulling) strength in the direction of the fibre.  The natural fibres – cotton, wool, silk – are typical. The lining-up is brought about by drawing – stretching — the return to random looping and coiling is overcome by strong intermolecular attractions.
E Elastomers	P Possesses the high degree of elasticity that is characteristic of rubber: it can be greatly deformed — stretched to eight times its original length e.g., Buna N and Buna S, When the stretching force is removed, the molecular chains of an elastomer do not remain extended and aligned but return to their original random conformations
T Thermoplastic polymers	S Soften on heating and stiffen on Cooling. e.g. polythene, polystyrene, PVC
Thermosetting polymers	Do not soften on heating and cannot be remoulded.  Example, Bakelite