Chapter 15 Polymers Solutions
Question - 11 : - Define the term polymerisation.
Answer - 11 : -
Polymerization is the process of forminghigh molecular mass (103 − 107 u)macromolecules, which consist of repeating structural units derived frommonomers. In a polymer, various monomer units are joined by strong covalentbonds.
Question - 12 : - Is 
,a homopolymer or copolymer?
Answer - 12 : - is a homopolymerbecause it is obtained from a single monomer unit, NH2−CHR−COOH.
Question - 13 : - In which classes, the polymers are classified on the basisof molecular forces?
Answer - 13 : -
On the basis of magnitude of intermolecular forces presentin polymers, they are classified into the following groups:
(i) Elastomers
(ii) Fibres
(iii) Thermoplastic polymers
(iv) Thermosetting polymers
Question - 14 : - How can you differentiate between addition andcondensation polymerisation?
Answer - 14 : -
Addition polymerization is the process of repeatedaddition of monomers, possessing double or triple bonds to form polymers. Forexample, polythene is formed by addition polymerization of ethene.
Condensation polymerization is the process of formation ofpolymers by repeated condensation reactions between two different bi-functionalor tri-functional monomers. A small molecule such as water or hydrochloric acidis eliminated in each condensation. For example, nylon 6, 6 is formed bycondensation polymerization of hexamethylenediamine and adipic acid.
Question - 15 : - Explain the term copolymerisation and give two examples.
Answer - 15 : -
The process of forming polymers from two or more differentmonomeric units is called copolymerization. Multiple units of each monomer arepresent in a copolymer. The process of forming polymer Buna−S from 1,3-butadiene and styrene is an example of copolymerization
Nylon 6, 6 is also a copolymer formed byhexamethylenediamine and adipic acid.
Question - 16 : - Write the free radical mechanism for the polymerisation ofethene.
Answer - 16 : -
Polymerization of ethene to polythene consists of heatingor exposing to light a mixture of ethene with a small amount of benzoylperoxide as the initiator.
The reaction involved in this process is given below
:Define thermoplastics and thermosetting polymers with twoexamples of each.
Answer - 17 : -
Thermoplastic polymers are linear (slightly branched) longchain polymers, which can be repeatedly softened and hardened on heating.Hence, they can be modified again and again. Examples include polythene,polystyrene.
Thermosetting polymers are cross-linked or heavilybranched polymers which get hardened during the molding process. These plasticscannot be softened again on heating. Examples of thermosetting plastics includebakelite, urea-formaldehyde resins.
Question - 18 : - Write the monomers used for getting the followingpolymers.
(i) Polyvinyl chloride (ii) Teflon (iii) Bakelite
Answer - 18 : -
(i) Vinyl chloride (CH2=CHCl)
(ii) Tetrafluoroethylene (CF2 =CF2)
(iii) Formaldehyde (HCHO) and phenol (C6H5OH)
Question - 19 : - Write the name and structure of one of the commoninitiators used in free radical addition polymerisation.
Answer - 19 : -
One common initiator used in free radical additionpolymerization is benzoyl peroxide. Its structure is given below.
Question - 20 : - How does the presence of double bonds in rubber moleculesinfluence their structure and reactivity?
Answer - 20 : -
Natural rubber is a linear cis-polyisoprenein which the double bonds are present between C2 andC3 of the isoprene units.
Because of this cis-configuration, intermolecularinteractions between the various strands of isoprene are quite weak. As aresult, various strands in natural rubber are arranged randomly. Hence, itshows elasticity.