Polythene, polyvinyl and polystyrene soften on heating and harden on cooling. Such polymers are called thermoplastic polymers. These possess intermolecular forces of attraction whose strength lies between strength of intermolecular forces of elastomers and. fibers. These polymers are linear or slightly.

During vulcanization, natural rubber is heated with 3-5% sulphur. The function of sulphur is to introduce sulphur (or disulfide) bridges or cross- links between polymer chains 
thereby imparting more tensile strength, elasticity, and resistance to abrasion

Addition polymers are those 'which are formed from unsaturated monomers without loss of small molecules like HP, NH3, etc., e.g. polyethene. Condensation polymers are those which are formed from monomers having multi-functional groups with the loss of small molecules like HP, NH3, etc., e.g. Nylon-66.

Polymers which can be repeatedly softened on heating and hardened on cooling and can be used again and again without any change in their chemical composition and mechanical strength are called thermoplastics. For example, polythene, Teflon, polystyrene, nylon, PVC, PAN, etc.

(i) Elastomers            
(ii) Fibres        
(iii) Thermoplastics
(iv) Thermosetting polymers.

(iii) CH₂=CH₂(Ethene)

(i) Elastomers: The polymers in which polymer chains are held together by the weakest intermolecular forces.These weak forces permit the polymer to be stretched.A few 'cross-links' are introduced in between the chains which held the polymer to retract to its original position after the force is released, as in vulcanised rubber
(ii) Condensation polymers: It involves a series of condensation reaction generally involving two monomers.Each monomer normally contains two functional groups.The condensation reactions result in the loss of small molecules usually water and ammonia, e.g. nylon, terylene, bakelite are condensation polymers.This  process is Known as 'condensation polymerisation'
(iii) Addition polymers: The polymers which are formed by repeated addition of monomers to the polymer chain.The monomers are unsaturated compounds and commonly derivatives of ethene.the addition polymers have same empirical as their monomers, e.g

This process is 'addition polymerisation'.

Biodegradable polymers: Those polymers which are biodegradable, i.e. decomposed by microorganisms and do not create water pollution, e.g. PHBV.
Poly (Glycolic acid) and Poly (Lactic acid) are biodegradable polymers such as sutures.Dextron was the first bioabsorbable suture made from biodegradable polyester for post operative stiches

The natural rubber is linear cis-1, 4-polyisoprene.The double bonds are located between C₂ and C₃ of isoprene units.This cis - configuration about double bonds do not allow the chains to come closer for effective attraction due to weak intermolecular force of attraction.That is why, the natural rubber has a coiled structure and shows elasticity.

SBR (styrene-butadiene rubber) is an addition copolymer.

(i) Main formaldehyde resins: Bakelite, melamine formaldehyde and urea Formaldehyde. 
(ii) Bakelite: Phenol and formaldehyde.
Melamine formaldehyde: Melamine and formaldehyde.
Urea formaldehyde: Urea and formaldehyde. 
(iii) Melamine is used for this purpose. 
(iv) In the modern world, polymer industry has a major role. No doubt, natural polymers are also useful but synthetic polymers have an impact on most of our daily house hold necessity items. It may range from kitchen, bed room and also all luxury items. But it is not worth to destroy plants as they are life giving.

(i) From the given passage, we can conclude that the students show awareness about the environment.
(ii) A polymer that can be decomposed by microorganisms within a definite period of time so that the polymer or its degraded product does not cause any harm to the environment, is called a bio-degradable polymer. For example, poly- \(\beta\)- hydroxybutyrate-co-\(\beta\)-hydroxy valerate.
(iii) Polythene is an addition polymer that is formed by the addition of ethene molecules.