Copolymers: Classification, Applications and Examples

Ans. Copolymers: Two or more monomeric species are involved. Example copolymerisation of butadiene styrene.

Homopolymers: Single monomeric species are present. Example homopolymerisation of polystyrene.

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1. Copolymer: Copolymer is formed when more than one species of an unsaturated monomer combines to polymerize. The process of forming such polymers is called copolymerization. Example: rubber, spandex, PEVA, etc. They can be formed by either of the two methods: chain-growth polymerization and step-by-step growth polymerization. 
2. Synthetic rubber: Synthetic Rubber is a more flexible vulcanized rubber-like polymer that is better to use than natural rubber because of its ability to stretch far more than a natural one. Synthetic polymers can be formed by the intervention of copolymerization and can either be homopolymer or copolymer. Example: Neoprene, Buna-S, Thiokol, Buna-N, etc. 

Ans. Option (v), Nylon 6,6 is a copolymer out of all. It is because as per the definition of copolymer, they have to be formed out of more than one species of monomers. But all the others are formed out of one species of monomer, except Nylon 6,6. 

Ans. Addition polymerization, one of the ways to form copolymers, incorporates the formation of polymers without any intermediate product (kind of like SN2 reaction in haloalkanes and arenes). They take place generally in the presence of a catalyst. Also known as chain-growth polymerization reaction, there is the direct addition of the monomeric subunits. 

Example: Using ethylene molecules to make polyethylene when the double bonds in ethylene break to give rise to single C-C bonds.

Ans. Condensation polymerization reaction, also known as step-by-step growth polymerization, that is involved in either method of copolymerization, happens between two different monomeric species (either bi-functional or tri-functional). Substances like water, alcohol, and ammonia are eliminated in the final product due to repeated condensation reactions.

Example: Nylon 6,6 which is obtained from hexamethylene diamine is condensed repeatedly with adipic acid. The pressure and temperature required for the condition to succeed are quite high. 

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• Spandex used as synthetic fibre is a block copolymer, other block polymers like polyester and polyamide TPEs have applications in hose tubing, sports goods and automotive components.
• Nylon -6-6- is frequently used in textiles, carpeting, as an engineering material in bearings and gears due to its self-lubricating properties.
• Graft polymers can be used as membranes to separate gas and liquids, they can also be used in emulsifiers and biomedical applications.

Ans. Periodic, Gradient, Block, Statistical and Alternating copolymers.

Alternating Copolymers: These copolymers have a regular, repetitive and alternating arrangement of two monomeric species, eg A and B.The general formula can be given as -(-A-B-)n- or -A-B-A-B-A-B-A-B-A-B-.

Examples: Nylon -6-6-

Statistical Copolymers: When the sequence of monomeric units follows a certain statistical rule it is called a statistical copolymer. Moreover, if the probability of finding a given monomer at a particular point in a chain is equal to its mole fraction in the chain then it can be called a random polymer.

Examples: Rubbers made from styrene-butadiene copolymers, resins from styrene acrylic etc.

Block Copolymers: When two or more homopolymer chains are joined by covalent bonds the resultant polymeric chain is called a Block copolymer.The intermediate unit where they join is called a junction block.They can be diblock or triblock copolymers.

Examples: Acrylonitrile butadiene styrene (SBS rubber).

Ans.  The functionality of a monomer implies the number of bonding sites present in it. For example, monomers like propene, styrene, acrylonitrile have the functionality of one which means that they have one bonding site.

Monomers such as ethylene glycol, hexamethylenediamine, adipic acid have the functionality of two which means that they have two bonding sites.

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1. Natural polymers: The polymers which occur in nature mostly in plants and animals are called natural polymers. A few common examples are starch, cellulose, proteins, rubber nucleic acids, etc. Among them, starch and cellulose are the polymers of glucose molecules. Proteins are formed from amino acids which may be linked in different ways. These have been discussed in detail in unit 15 on biomolecules. Natural rubber is yet another useful polymer which is obtained from the latex of the rubber tree. The monomer units are of the unsaturated hydrocarbon 2-methyl-i, 3-butadiene, also called isoprene. Examples of natural polymers: Natural rubber, cellulose, nucleic acids, proteins etc.
2. Synthetic polymers: The polymers which are prepared in the laboratory are called synthetic polymers. These are also called man-made polymers and have been developed in the present century to meet the ever-increasing demand of modern civilization. Examples of synthetic polymers: Dacron (or terylene), Bakelite, PVC, Nylon-66, Nylon-6 etc.

Ans. Polymers are high molecular mass substances (103 — 107u) consisting of a very large number of simple repeating structural units joined together through covalent bonds in a linear fashion. They are also called macromolecules. Ex: polythene, nylon 6,6, bakelite, rubber, etc.