Polymers classification Based on Source
Natural Polymers: These polymers are found in plants and animals. Examples are proteins, cellulose, starch, resins and rubber
Semi-synthetic Polymers: Cellulose derivatives as cellulose acetate acetate (rayon) (rayon) and cellulose cellulose nitrate, nitrate, etc. are the usual examples examples of this sub category
Synthetic Polymers: A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon 6,6) and synthetic rubbers (Buna – S) are examples of man-made polymers
Classification Based on Backbone of the polymers chain
Organic and Inorganic Polymers: A polymer whose backbone chain is essentially made of carbon atoms is termed as organic polymer The atoms attached to the side valencies of the backbone carbon atoms are, however, however, usually usually those of hydrogen, hydrogen, oxygen, oxygen, nitrogen, nitrogen, etc. The majority of synthetic polymers are organic On the other hand, generally chain backbone contains no carbon atom is called inorganic polymers Glass and silicone rubber are examples of it.
Classification Based on Structure of Polymers
Linear Polymers: These polymers consist of long and straight chains. The examples are high density polythene, PVC, etc. Linear polymers are commonly relatively soft, often rubbery substances, and often likely to soften (or melt) on heating and to dissolve in certain solvent .
Branched Polymers: These polymers contain linear chains having some branches, e.g., low density polythene .
Cross-linked Polymers: These are usually formed from bi-functional and tri-functional monomers and contain strong covalent bonds between various linear polymer chains, e.g. vulcanized rubber, urea-formaldehyde resins, etc. Cross linked polymers are hard and do not melt, soften or dissolve in most cases.
Classification Based on Composition of Polymers
Homopolymer: A polymer resulting from the polymerization of a single monomer; a polymer consisting substantially of a single type of repeating unit .
Copolymer: When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer.
Classification Based on Mode of Polymerisation
Addition Polymers: 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 homopolymer, e.g., polythene The polymers made by addition polymerisation from two different monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc
Condensation Polymers: The condensation polymers are formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units In these polymerisation reactions, the elimination of small molecules such as water, alcohol, hydrogen chloride, etc. take place The examples examples are terylene terylene (dacron), (dacron), nylon 6, 6, nylon 6, etc For e.g., nylon 6, 6 is formed by the condensation of hexamethylene diamine with adipic acid It is also possible, with three functional groups (or two different monomers at least one of which is tri-functional), to have long linkage sequences in two (or three) dimensions and such polymers are distinguished as cross linked polymers.
Polymers classification Based on Molecular Forces
The mechanical properties of polymersare governed by intermolecular forces, e.g., van der Waals forces and hydrogen bonds, present in the polymer, these forces also bind the polymer chains Under this category, the polymers are classified into the following groups on the basis of magnitude magnitude of intermolecular intermolecular forces present present in them, they are: Elastomers, Fibers, Liquid resins, Plastics (which includes Thermoplastic and thermosetting plastic)
These are rubber – like solids with elastic properties In these elastomeric polymers, the polymer chains are random coiled structure, they are held together by the weakest intermolecular forces , so they are highly amorphous polymers These weak binding binding forces permit the polymer polymer to be stretched stretched 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 The examples are buna-S, buna-N, neoprene, etc
If drawn into long filament like material whose length is at least 100 times its diameter, polymers are said to have been converted into ‘fibre’ Polymeric chains are straight chain polymers, they are held together by the strong intermolecular forces like hydrogen bonding, these strong forces also lead to close packing packing of chains and thus impart crystalline nature Fibres are the thread forming solids which possess high tensile strength and high modulus Examples are polyamides (nylon 6, 6), polyesters (terylene), etc.
Polymers used as adhesives, potting compound sealants, etc. in a liquid form are described liquid resins, examples are epoxy adhesives and polysulphide sealants.
A polymer is shaped into hard and tough utility articles by the application of heat and pressure; it is used as a ‘plastic’ The intermolecular force between polymeric chains are intermediate between elastomers and fibers, so they are partially crystalline.
Typical examples are polystyrene, PVC and polymethyl methacrylate. They are two types: Thermoplastic and Thermosetting plastic.
Some polymers soften on heating and can be converted into any shape that they can retain on cooling The process of heating, reshaping and retaining the same on cooling can be repeated several times, such polymers, that soften on heating and stiffen on cooling, are termed ‘thermoplastics’ These are the linear or slightly slightly branched branched long chain molecules molecules capable of repeatedly softening on heating and hardening on cooling These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres Polyethylene, PVC, nylon and sealing wax are examples of thermoplastic polymers.
Some polymers, on the other hand, undergo some chemical change on heating and convert themselves into an infusible mass They are like the yolk of egg, which on heating sets into a mass, and, once set, cannot be reshaped. Such polymers, that become infusible and insoluble insoluble mass on heating, heating, are called ‘thermosetting” ‘thermosetting” polymers polymers. These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins, etc.