General introduction and classification of polymers, general methods of polymerization - addition and condensation, copolymerization; Natural and synthetic rubber and vulcanization; some important polymers with emphasis on their monomers and uses - polythene, nylon, polyester and bakelite.
A polymer is a large molecule built by repetitive binding together of many small units called monomers.
Homopolymer: A polymer derived from a single repeating monomer. Only one type of monomer will have repetitive binding and a large molecule appears.
Copolymer: When two or more monomer bind together in a repetitive manner and give rise to a large polymer, it is called copolymer.
Synthetic polymers are categorised as Chainr growth polymers and step growth polymers based on the method of preparation.
Chain growth polymers: Also called addition polymers.
Step Growth polymerss: Also called as condensation polymers
Classification based on physical properties
Properties and uses Natural rubber
Rubber is a naturally occuring polymer. It is obtained as latex from rubber trees. It is highly elastic.
It is a polymer of isoprene (2-methyl buta-1,3-diene)
In natural rubber, about 11,000 to 20,000 isoprene units are linked together in a chain like arrangement.
Natural rubber is a thermoplastic. It becomes soft and sticky when heated. It is not hard and tough.t The properties can be modified and improved by the process of vulcanization.
Properties and uses cellulose
Properties and uses nylon
The monomer of nylon 6 is caprolactum.
fabrics, ropes and tyre cords are prepared using nylon 6.
For nylon 66, the monomers are hexamethylenediamine and adipic acid.
Bristles for brushes, and textile sheets are made using nylon 66
Properties and uses teflon
It is an addition polymer of tetrafluoroethylene.
nF2C=CF2 under heat and pressure (-F2C-CF2-)n
The double bond breaks and gets ready for bonding with a carbon on either side and the polymerisation takes place.
It is a tough material and is resistant towards heat, action of chemicals such as acids and bases. It is bad conductor of electricity.
Properties and uses PVC.
PVC is polyvinyl chloride
Its monomer is vinyl chloride. CH2=CHCl
PVC is prepared by heating vinyl chloride in an inert solvent in the presence of peroxides ( for instance, dibenboyl peroxide)
The double bond breaks and becomes ready bonding to carbon on either side and polymerisation takes place.
PVC is hard horny material. It is a thermoplastic polymer andits plasticity can be increased by the addition of plasticizer usch n-butylphthalate.
PVC is used in the manufacture of rain coats, hand bags, curtain clothes,and toys.
It is also used in articial flooring, as an insulating material in electric wires and for making gramophone records.