Class 12 chemistry chapter 15 deal with the study of polymers their formation, classification and their uses. Polymers are high molecular mass macromolecules, which contains repeating structural units derived from the corresponding monomers. Polymers are also termed as macromolecules due to their large size but the converse is not always true. A macromolecule may or might not contain monomer units. Such as chlorophyll is a macromolecule but not a polymer since there are no monomers, units present. As a result, we can say that all polymers are macromolecules but not all macromolecules are polymers in nature. The process of formation of a polymer by joining many monomers together is termed as polymerisation.
We classify polymers on various aspects based on their source of origin, on their structure, on their mode of polymerisation, on their molecular forces and on growth polymerisation. Polymers origin may be natural or synthetic and based on the source of origin polymers can be of 3 types natural, semi-synthetic and synthetic polymers. Natural polymers are the polymers, which we derive, from the plants and animals whereas synthetic polymer is those which we prepare in the laboratory. Semi-synthetic polymers are obtained by modifying the natural polymers. Similarly based on their structure polymers are of 3 types linear, branched and cross-linked polymers.
Polymers are classified based on the mode of polymerisation polymers undergoes two types of polymerisation- addition and condensation. In the presence of an organic peroxide initiator, the alkenes and their derivatives undergo addition polymerisation or chain growth polymerisation through a mechanism termed as the free radical mechanism. This mechanism consists of three steps, which are chain-initiating step, chain propagating step and chain terminate step. Polythene, Teflon, etc. are formed by addition polymerisation of alkenes or its derivative. A condensation polymerisation reaction generally involves a repetitive condensation reaction between two bi-functional monomers containing – NH2, – OH and – COOH groups.
In this type of polymerisation may result in the loss of some simple molecules, and lead to the formation of high molecular mass condensation polymers. Formaldehyde reacts with phenol and melamine to make the corresponding condensation polymer products. The condensation polymerisation is also termed as step-growth polymerisation because it progresses through the step-by-step method. Nylon, Bakelite are some of the examples of condensation polymers. Copolymerisation is a polymerisation reaction in which a mixture of more than one monomer is allowed to polymerise and form a copolymer.
Natural rubber is a natural polymer, which has elastic properties and we obtain it from the bark of a rubber tree. It is a linear polymer of isoprene, which is also termed as cis 1, 4-polyisoprene. Natural rubber made tougher by the process of vulcanisation with sulphur. Polymers obtained by copolymerisation of alkene and 1, 3 butadiene derivatives are termed as synthetics rubber. As we, all know about the environmental hazards of synthetic polymeric wastes, to reduce the harmful effects biodegradable synthetic polymers have been designed and developed.
Biodegradable polymers such as PHBV and Nylon-2- Nylon-6 are alternatives to the polymers. The action of microorganism can degrade them. We use polymers in making toys, ropes, insulator, wrapping material. Bakelite is useful for making electrical switches and handles of the utensils. Some more uses of polymers are in making paints such as Glyptal. PVC is in use for making raincoat, handbags, vinyl flooring, water pipes.