Properties and uses of some important polymers:
Main Topics Covered in the TMH Book
SOME EXAMPLES OF STEP-GROWTH POLYMERS
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 different monomers bind together in a repetitive manner and give rise to a large polymer, it is called copolymer.
Classification of Polymers
Classification based on source:
Natural and synthetic
Classification based on structure:
2. Branched chain polymers
3. Cross linked polymers
Classification based on molecular forces and physical properties
4. Thermosetting polymers
Classification based on mode of synthesis:
1. addition polymers
2. Condensation polymers
Methods of Polymerisation
Synthetic polymerisation processes are categorised as Chain growth and step growth polymerisation.
Chain growth polymerisation: Also called addition polymerisation.
In this process, the combination of monomers does not result in elimination of some by product molecules. The process is initiated by by a free radical, a cation or an anion and once initiated, the process gets repeated as a chain reaction as the process produces bigger and bigger active molecules.
1. Initiator --> I* a reactive species
2. I* + M (monomer) --> IM* (bigger reactive species)
3. IM* + M --> IMM*
4. IMM* + M --> IMMM*
The chain stops when the active end reacts with a species giving a molecule without the reactive end.
Many vinyl polymers (Vinyl indicates compounds having double bonds) are formed by chain growth polymerisation (chain reaction polymerisation).
Step Growth polymerisation: Also called as condensation polymerisation
In condensation polymerisation, two or more different monomers combine together and in this process of combination elimination of simple molecules like water, ammonia, hydrogen chloride etc. takes place. So there is a condensation in this process of polymerisation.
In this polymerisation generally the monomers contain two functional monomers (difunctional monomers). In this process, the polymerisation takes place step by step.
A + B --> A-B
A-B + A --> A-B-A
A-B-A + B --> A-B-A-B
It can also be
A-B + A-B --> A-B-A-B
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.
A set of questions on this chapter posted in