Q.51 Classify the following as elastomers and fibres nylon-6,6, terylene, buna-S, buna-N.
Answer: (i) Nylon 6,6- Fibre (ii) Terylene - Fibre (iii) Buna-N- Elastomer (iv) Buna-S- Elastomer
Q.52 Arrange the following polymers in order of increasing intermolecular force. Bakelite, Nylon-6,6, Polythene, Neoprene.
Answer: Neoprene < Polythene < Nylon 6,6 < Bakelite.
Q.53 How polymers are different from macromolecules? Explain with example.
Answer: A polymer always consists of large number of repeating structural units but a macromolecule may or may not consist of repeating structural units. e.g. Proteins and nucleic acids should be regarded as macromolecules but not polymer since their molecules do not contain repeating structural units where as cellulose is a polymer because it contains P-D-glucose as repeating units.
Q.54 Why always purest monomer is used in free radical polymerization?
Answer: If impurity is present then alkene monomers may act as chain transfer agents or chain inhibitors. Therefore, the monomer in free radical polymerization is taken as pure.
Q.55 Which property is used to determine the molecular mass of polymers?
Answer: Physical and chemical properties are used to determine the molecular mass of polymers.
Q.56 Which type of polymerization gives a polymer containing carbon atoms only in the main chain?
Answer: Addition polymerization gives a polymer containing carbon atoms only in the main chain.
Q.57 Which type of polymerization gives a polymer containing hetero atoms?
Answer: Condensation polymerization gives a polymer containing hetero atoms.
Q.58 Name a substance which inhibits free radical polymerization.
Answer: Benzoquinone inhibits free radical polymerization. For structure and details, consult section 16.2.
Q.59 To which class of polymers does Nylon-6,6 belong?
Answer: It is a condensation polymer and is polymide in nature.
Q.60 What is mode of free radical polymerisation in alkenes?
Answer: It is addition polymerisation. For details, consult section 16.2.
Q.61 Write the structures of the monomers used for getting the following polymers? (a) PVC (b) Teflon (c) PMMA
Answer: (a)CH2=CHCl (b) CF2=CF2 (c)
Q.62 Why should one always use purest monomer in free radical polymerisation?
Answer: Impurities of other substances if present, may inhibit or hinder the chain propagation. They can also act as chain transfer agents and inhibit or even terminate the original chain reaction.
Q.63 Why does styrene undergo anionic polymerisation easily?
Answer: In styrene, an electron withdrawing phenyl group is present. As a result, the nucleophile or anionic attack can easily take place leading to anionic polymerisation.
Q.64 Why is cationic polymerisation preferred in case of vinylic monomers containing electron donating groups?
Answer: Electron donating groups tend to increase the electron density on the monomer unit. As a result, cationic attack can easily take place. For example, cationic polymerisation in propene with an electron releasing CH3 group with+I effect.
Q.65 Depict a free radical mode of addition polymerisation in isoprene.
Answer: Free radical polymerisation in isoprene is initiated by a free radical attack.
Free radicals participate in further polymerisation.
Q.66 Why are the numbers 6,6 and 6 put in the names of nylon 6,6 and nylon 6?
Answer: These numbers indicate the number of carbon atoms in the monomer units involved in the two varieties of nylon. nylon 6,6 : Adipic acid (six 'C' atoms) and hexamethylene diamine (six 'C' atoms) nylon 6 : ε-Aminocaproic acid.
Q.67 Polymers are always macromolecules but macromolecules are not always polymers. Explain.
Answer: In polymers, monomers which participate may be either same (homo polymers) or different (co-polymers). These are all macromolecules in nature. Biopolymers such as starch, proteins and nucleic acids are also macromolecules. But some macromolecules like chlorophyll, haemoglobin etc. do not have any monomer units and are not polymers.
Q.68 Can a co-polymer be formed both in addition and condensation polymerisation?
Answer: Yes it can be formed in both the cases. For example, Buna-S is a copolymer of styrene, 1, 3-butadiene and sodium and is an addition polymer. Nylon-6,6 is a condensation co-polymer in which monomers are different. i.e., adiptic acid and hexamethylene diamine.
Q.69 Explain how does 1, 3-butadiene polymerise by different routes.
Answer: Butadiene is a conjugated diene and its free radical polymerisation can occur in two ways: (i) When the polymerisation takes place at C1 and C4 of butadiene, an unbranched polymer results. It can exist either as trans-polybutadiene or as cis isomer or as the mixture of both.
(ii) 1, 3 butadiene can also undergo polymerisation at C1 and C2 to give polyvinyl polyethene as the product.
Q.70 Are polyesters and polyacrylates same? Justify your answer.
Answer: Polyesters and polyacrylates are different types of polymers and differ in the following characteristics. (i) Polyacrylates are homo polymers while the polyesters are co-polymers in nature. (ii) The mode of synthesis of polyacrylates is addition polymerisation while that of polyesters is condensation polymerization. (iii) Polymerization occurs across C=C bond in polyacrylates whereas in polyesters it is through ester linkage.
Q.71 Write the structures of the monomers of the following polymers :
Q.72 Draw the repeating structural units of the step-growth polymers you would expect to obtain from the following reactions.
Answer: (a) −CH2CH2CH2O− (b) −OCH2CH2O−CO(CH2)6CO−
Q.73 (a)Is a homo polymer or a copolymer? (b) Is it an addition or condensation polymer?
Answer: (a) The repeating structural unit of the given polymer contains only one type of monomer unit, i.e. styrene, C6H5CH=CH2, therefore, it is a homo polymer. (b) Since the monomer contains a double bond, and the polymer does not, therefore, it is an addition polymer.
Q.74 (a) Can a copolymer be formed in both addition and condensation polymerization? Explain. (b) Can a homo polymer be formed in both addition and condensation polymerization? Explain.
Answer: (a) Yes, copolymers can be formed both in addition and condensation, polymerization. For example, Buna- S is an addition copolymer of styrene and 1, 3-butadiene while nylon-6, 6, bakelite and polyester are condensation copolymers. (b) Yes, homo polymers can be formed both in addition and condensation polymerization. For example, polythene, PVC, PMMA, PAN, neoprene, etc. are examples of addition homo polymers while nylon-6 is an example of condensation homo polymer.
Q.75 How does the presence of benzoquinone inhibit the free radical polymerization of a vinyl derivative?
Answer: Benzoquinone reacts with radical of the growing polymer chain (R⋅) to form a new radical (I) which is extremely unreactive since it is highly stabilized by resonance. Because of the lack of reactivity of this new radical further growth of the polymer chain is interrupted and hence the reaction stops.
Q.76 Differentiate the following pairs of polymers based on the property mentioned against each. (i) Novolac and bakelite (structure). (ii) Buna-S and terylene (intermolecular forces of attraction).
Answer: (i) Novolac is a linear but bakelite is a cross- linked polymer of phenol and formaldehyde. For structures refer to pages 15/14-15/15.
(ii) Terylene contains ester functional groups which are polar in nature. Therefore, the intermolecular forces of attraction involved in terylene are strong dipole-dipole interactions as shown below :
Buna-S, on the other hand, does not have polar functional groups. It has only non-polar hydrocarbon chains and hence has only weak Van der Waals forces of attraction as shown below :
Q.77 State the significance of numbers 6 and 6, 6 in the polymer names nylon-6 and nylon-6, 6. or In nylon 6, 6 what does the designation 6, 6 mean.
Answer: Nylon-6 means that it is a condensation polymer of only one type of monomer molecules containing six carbon atoms, i.e., caprolactam. Nylon-6, 6, on the other hand, implies that it is a condensation polymer of two types of monomer molecules each containing six carbon atoms, i.e., adipic acid(HOOCCH2CH2CH2CH2COOH) and hexamethylenediamine (H2NCH2CH2CH2CH2CH2CH2NH2).
Q.78 What is the repeating unit in the condensation polymer obtained by combining HO2CCH2CH2COOH (succinic acid) and H2NCH2CH2NH2 (ethylenediamine).
Answer: The repeating structural unit is obtained by condensing at both ends of both the bifunctional molecules, i.e., Succinic acid (HOOCCH2CH2COOH) and ethylenediamine with the elimination of water molecules, i.e., −OCCH2CH2CO−NHCH2CH2NH-.