Summary
Key terms
Polymers: Polymers are the high molecular mass compounds, obtained by joining together a large number of simple repeated molecules through covalent bonds in a regular fashion.
Monomer: The smaller repeating unit in a polymer are known as monomer units.
Polymerisation: The process of formation of polymers from the simple starting materials (monomers) is called as polymerisation.
Homopolymer: It is formed by the polymerisation of one type of monomer units.
Copolymer: When two different types of monomers are joined in the same polymeric chain, the polymer is called a copolymer.
Buna rubbers: Synthetic rubbers obtained from butadiene are called buna rubbers.
Key concepts
- Polymers are defined as high molecular mass macromolecules, which consist of repeating structural units derived from the corresponding monomers through a process of polymerization. These polymers may be of natural or synthetic origin and are classified in a number of ways such as origin, type of monomer, structure etc.,
- Polythene, teflon, orlon, etc. are formed by addition polymerization or chain growth polymerization of alkenes and their derivatives through a free radical mechanism, catalyzed by peroxides.
- Condensation polymers are any kind of polymers formed through a condensation reaction where molecules join together losing small molecules as by – products such as water or alcohol etc.,. The condensation polymerisation progresses through step by step and is also called as step growth polymerization. Nylon, bakelite and dacron are some of the important examples of condensation polymers.
- A homopolymer contain same monomer units through out. However, a mixture of two unsaturated monomers exhibits copolymerization and forms a co – polymer containing multiple units of each monomer.
- Natural rubber is a cis 1, 4 – polyisoprene and can be made more tough by the process of vulcanisation with sulfur. Synthetic rubbers are usually obtained by copolymerization of alkene and 1, 3 butadiene derivatives.
- Thermoplastic polymers such as polyethene ( PE ), polypropylene( PP ) etc., are linear, long chain polymers, which can be softened on heating and hardened on cooling reversibly. Thermosetting polymers such as phenol – formaldehyde resins become hard and infusible on heating.
- In view of the potential environmental hazards of synthetic polymeric wastes, certain biodegradable polymers such as polylactide (PLA) and polyhydroxyalkanoates (PHA) are developing. Biodegradable plastics are environment – friendly, they have an expanding range of potential applications and are driven by the growing use of plastics in packaging.